Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: Particle Interrogation Devices and Methods
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to sampling and concentrative apparatus and methods for
collection
of trace analytes from surfaces and substrates where the analyte is in the
form of a
particulate, a particulate combined with a vapor, or a free vapor and
particularly to such
apparatus and methods as are useful in surveillance for trace explosives
residues.
There is a need for inspection and sampling of persons, articles of clothing,
buildings,
furnishings, vehicles, baggage, cargo containers, dumpsters, packages, mail,
and the like
for contaminating residues (termed here more generally "trace analytes") that
may
indicate chemical, radiological, biological, illicit, or infectious hazards.
Applications
involve detection of trace materials, both particles and optionally vapors,
associated with
persons who have handled explosives, detection of toxins in mail, or detection
of spores
on surfaces, while not limited thereto.
Current methods for surface sampling often involve contacting use of swabs or
liquids,
but methods for sampling by "sniffing" are preferred. To inspect mail or
luggage for
example, the sampling method of US Pat. No. 6,887,710 involves first placing
the article
or articles in a box-like enclosure equipped with airlocks, directing a blast
of air onto the
exposed surfaces in order to dislodge particles associated with the articles,
then sampling
the gaseous contents of the box by drawing any resulting aerosol through a
sampling port.
However, the process is inherently slow because each article or person must be
moved
into the box or chamber and the box sealed before sampling, an obvious
disadvantage
when large numbers of articles or persons must be screened, or when the
articles are
larger than can be reasonably enclosed, such as a truck, shipping container,
or the
hallway surfaces of a building. Similar comments may be made regarding the
teachings
of US 6,324,927 to Ornath, where an enclosed shaker is used to dislodge
particles.
An approach for sampling persons is seen in US Pat. No. 6,073,499 to Settles,
aspects of
which are also discussed in "Sniffers: fluid dynamic sampling for olfactory
trace
detection in nature and homeland security", J Fluids Eng 127:189-218.
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McGown in US Pat, No. 4,909,090 describes a hand-held vapor sampler,
optionally with
a shroud for enclosing a sampling space, for using low pressure puffs of hot
air to
vaporize illicit substances on surfaces and trap any vapors on a collector
coil. The coil
contains ribbon-like windings of metal which have a thin coating of material
such as an
organic polymer effective in absorbing organic molecules such as cocaine.
However,
particles are not sampled and would not be successfully aspirated under the
conditions
described, which relies on a 250 Watt lamp and a spring-actuated plunger for
generating
a puff of air. Improvements to the collector/desorber device are disclosed in
US
5,123,274 to Carroll.
Ishikawa in US Pat. No. 7,275,453 discloses a cover enclosure in contact with
a surface,
the enclosure with internally directed jet for operatively flushing and
ejecting particles
from the surface. The particles may be collected by means of an inertial
impactor and
thermally gasified from the impactor for detection of chemical constituents by
mass
spectroscopy. Use of a plate-type inertial impactor avoids the need for a fine-
mesh filter,
such as would become clogged.
Various particle and vapor traps are disclosed in patents to Linker of Sandia
Labs,
including US RE38,797 and US Pat. Nos. 7,299,711, 6,978,657, 6,604,406,
6,523,393,
6,345,545, 6,085,601 and 5,854,431, by Corrigan in US Pat. Nos. 5,465,607 and
4,987,767, and Syage in US Pat. No. 7,299,710, but implementation has proved
difficult
because particles have been found to poison commonly used vapor trap materials
and
means for efficiently separating particles and vapors are not recognized.
Teachings by Hitachi in US Pat. No. 7,275,453 relate to an unusual inertial
impactor with
central void for discarding particles in excess of the cut size of the
impactor. This has the
unfortunate effect of dramatically reducing the amount of analyte available
for detection.
Also disclosed is a heatable rotary trap, as has longstandingly been known in
the art.
Detection technologies are known. Of particular interest for detection of
explosives are
electron capture (often combined with gas chromatography), ion mobility
spectroscopy,
mass spectroscopy, and chemiluminescence (often combined with gas
chromatography).
One common analytical instrument for detection of nitrate-type explosives
relies on
pyrolysis followed by redox (electron capture) detection of NO2 groups
(Scientrex EVD
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3000), but is prone to false alarms. Also of interest is differential mobility
spectroscopy
as described in US 7,605,367 to Miller. Ion mobility spectroscopic (IMS)
detectors are in
widespread use and typically have picogram sensitivity. IMS requires
ionization of the
sample, which is typically accomplished by a radioactive source such as Nickel-
63 or
Americium-241. This technology is found in most commercially available
explosive
detectors like the GE VaporTracer (GESecurity, Bradenton, FL), Sabre 4000
(Smiths
Detection, Herts, UK), Barringer IonScanTM 400, and Russian built models.
The luminescence of certain compounds undergoing reaction with electron-rich
explosive
vapors has been improved with the introduction of amplifying fluorescent
polymers as
described in US Pat. No. 7,208,122 to Swager (ICx Technologies, Arlington VA).
Typically vapors are introduced into a tubular sensor lined with a conductive
quenchable
fluorescent polymer by suction. These sensors lack a pre-concentrator and work
only for
analytes with electron-donating properties. More recent advances have extended
work
with fluorescent polymers to include boronic peroxide-induced fluorescence, as
is useful
for detecting certain classes of explosives.
Other analytical modalities are available, and include the MDS Sciex CONDOR,
Thermedics EGIS, Ion Track Instruments Model 97, the Sandia Microhound,
Smith's
Detection Cyranose, FIDO (FLIR Systems, Arlington VA, formerly ICx
Technologies),
Gelperin's e-nose (US Pat No 5,675,070), Implant Sciences' Quantum Sniffer,
and
others. However, these technologies are associated with aspiration and
analysis of
vapors, which are typically in vanishingly small concentrations, either
because a) the
vapor pressure of the material is inherently small, or b) if vapor pressure is
larger, then
significant quantities of a more volatile analyte will have been lost due to
ageing of the
material prior to sampling. Some of these detectors also have had maintenance
issues,
often related to fouling due to aspiration of particles.
Aerodynamic focusing has been used to produce particle beams or ribbons in a
gas
stream, process in which the gas streamlines are separated into a particle-
depleted sheath
flow and a particle-enriched flow. The two flows can then be separated,
resulting in
particle concentration. An aerodynamic lens particle concentration system
typically
consists of four parts: a flow control orifice, at least one focusing lenses,
an acceleration
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nozzle, and a skimmer. The choked inlet orifice fixes the mass flow rate
through the
system and reduces pressure from ambient to the value required to achieve
aerodynamic
focusing. The focusing lenses are a series of orifices contained in a tube
that create a
converging-diverging path resulting in flow accelerations and decelerations,
through
which particles are separated from the carrier gas due to their inertia and
focused into a
tight particle beam or ribbon. The accelerating nozzle controls the operating
pressure
within the lens assembly and accelerates particles to downstream destinations.
The
skimmer is typically a virtual impactor with virtual impactor void for
collecting the
particle beam or ribbon while diverting the greater mass of the particle-
depleted bulk
flow, thus concentrating the particle fraction.
Focusing of a range of micron and submicron size aerosol particles has been
carried out
using aerodynamic forces in periodic aerodynamic lens arrays [see Liu et al,
1995,
Generating particle beams of controlled dimensions and divergence, Aerosol
Sci. Techn.,
22:293-313, Wang, X et al, 2005, A design tool for aerodynamic lens system,
Aerosol
Sci Techn 39:624-636; US Pat. Appl. Doc. 2006/0102837 to Wang]. Such arrays
maybe
used as inlets to on-line single-particle analyzers [see Wexler and Johnston
(2001) in
Aerosol Measurement: Principles, Techniques, and Applications, Baron and
Willeke eds,
Wiley, New York, and US Pat. No. 5,565,677 to Wexler]. As known in the art, a
major
class of skimmers generally comprise a cone or plate with a hole in the center
(i.e., are
virtual impactors).
Aerodynamic lenses have been used in particle mass spectrometers and as an
adjunct to
ion mobility spectroscopy, (for example as described in US Pat. Nos.
7,256,396,
7,260,483, and 6,972,408 and more recently in US Pat. 2010/025273 1), where
high
vacuum is used (0.1 to 30 mTorr). In this system, analyte vapors released from
a very
well collimated particle beam (typically <0.25 mm diameter) are laser ablated
and
ionized in flight and the resulting vapors are conveyed in a buffer gas at
high vacuum,
typically with Einzel lensing, to a mass spectrometer or an ion mobility
spectrometer.
The downstream analyzer can be badly damaged by the entry of intact particles.
Moreover, the particle-by-particle approach taught in the art substantially
limits
application for high throughput analysis and is not scaleable except by an
impractical
redundancy of parallel systems.
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Related systems are described in PCT Publication WO/2008/049038 to Prather, US
Pat.
No. 6,906,322 to Berggren, and US Pat. No. 6,664,550 to Rader. However, these
devices are readily overloaded when confronted with large amounts of complex
mixtures,
interferents, and dust, such as are likely to be encountered in routine use.
Thus, strategies are needed to improve analyte collection efficiency and avoid
interferences. There is a need for a front end device with directional head
for
mobilization of particles from substrate to aerosol, a head that can be
portably directed to
dislodge particles and optionally vapor residues from target surfaces, then
efficiently
capture and concentrate them before presentation to an analytical instrument
of choice, an
approach that optimizes sensitivity and can speed deployment because the need
to
enclose the target surface in a sealed chamber or shroud is overcome. In
particular, there
is a need for a front end collection system that may be used in environments
where a
small amount of a target analyte must be detected in the presence of larger
amounts of
ubiquitous background particulates, for example dust and water with small
amounts of
target analyte, and with means for regenerating capture surfaces.
The preferred devices, systems and methods overcome the above disadvantages
and
limitations and are useful in detecting hazardous particles, vapors and
volatiles associated
with objects, structures, surfaces, cavities, vehicles or persons.
SUMMARY
Disclosed is a pneumatic sampler head with "virtual sampling chamber" for
sampling
hazardous contaminants such as traces of explosives, infectious agents, or
toxins on
persons, articles of clothing, buildings, furnishings, vehicles, cavities,
dumpsters, cargo
containers, baggage, packages, mail, and the like.
A first system includes a sampler head with a central collection intake
operated under
suction and an array of jet nozzles directed convergingly toward the apex of a
virtual
cone extending from the sampler head. A virtual sampling chamber is formed
when
streamlines of gas discharged by the jet nozzle array impinge on an external
surface. The
jets serve to dislodge and mobilize particulate and vapor residues on a
surface and the
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suction intake draws them into the sampler head. Use of the jet-enclosed
virtual
sampling chamber extends and directs the reach of the suction intake, which
would
otherwise draw air from behind the intake.
Surprisingly, gas jets operated in a millisecond-scale pulse mode are found to
be more
effective than gas jets operated continuously in collecting particulate and/or
vapor
residues with the sampler head. The virtual sampling chamber may be formed and
collapsed in less than a second in response to a single synchronized jet pulse
while under
suction, or may be formed intermittently, such as by a train of synchronized
pulses
separated by a fraction of a second or longer, during operation. The sampler
head may be
compact for portable hand-directed operation or scaled up and operated
robotically for
screening of vehicles, cargo containers, and so forth, while not limited
thereto.
In one sampling system, the apparatus is a pneumatic sampler head for sampling
residues,
including particulate and vapor residues, from an external surface of an
object, structure,
vehicle or person, which comprises a) a sampler head with forward face and
perimeter; b)
a suction intake port disposed centrally on the forward face and an array of
two or more
jet nozzles peripherally disposed on the forward face around the suction
intake port,
wherein the jet nozzles are directed at a virtual apex of a virtual cone with
base resting on
the forward face; c) a positive pressure source for firing or propelling a gas
sampling jet
pulse or stream with streamlines from each nozzle of the array of jet nozzles;
d) a suction
pressure source for drawing a sampling return stream of gas into the suction
intake port,
the suction pressure source having an inlet and an outlet; where the
streamlines of the gas
sampling jet pulses are directed toward the virtual apex of the virtual cone,
the
streamlines tracing an involuted frustroconical "U-turn" under the attraction
of the
suction pressure source and converging with the sampling return stream at the
suction
intake port along a central axis of the virtual cone when impinging on the
external
surface.
The out-flow of the gas sampling jets and in-flow of the sampling return
stream form a
"virtual sampling chamber" with the gas sampling jet pulses directed linearly
along the
walls of the virtual cone toward its apex and the sampling return stream
directed along
the central axis of the virtual cone toward its base, and further wherein the
involuted
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frustroconical "U" fluidly connects the gas sampling jets and the sampling
return stream
at a virtual frustrum when impinging on an external surface. In preferred
embodiments
the device is operative at up to 1 foot from the external surface.
Surprisingly, we have found that pneumatic pulses or streams emitted from a
concentric
array of gas interrogation jet nozzles directed in trajectories along the
walls of a virtual
cone will turn inward when directed at a surface and return to a common
suction intake
port mounted in the sampler head in the center of the jet array. The sampler
head maybe
held at a distance and aimed at the surface to be interrogated. Targetable jet
nozzles and
laser guidance may be used to shape the pulse geometry if desired. Particles
or vapors
removed from the interrogated surface are efficiently mobilized in the
"virtual sampling
chamber" and aspirated through the suction intake, where they may then be
concentrated
and analyzed by a variety of methods.
In use, pneumatic pulses initially follow directional vectors converging along
the virtual
"walls" of a "virtual cone", but upon contact with a surface disposed at a
distance from
the base of the cone Dr which is less than the height of the cone D, a virtual
frustrum is
formed by involution of the streamline vectors so that the streamlines flow
back along the
central axis of the cone into an intake duct centrally mounted on the face of
the sampler
head. The virtual cone thus becomes a closed "virtual sampling chamber" where
objects
or surfaces brought within the cone are stripped of volatiles and loose
particulates and
carried into the sampler head. Once entrained in the suction intake, particles
or vapors in
the stream of air may be concentrated for collection or analysis.
Sampling jet and suction intake gas flows may be discontinuous or continuous,
balanced
or imbalanced, subsonic or sonic in character. In one application, the in-
flows and out-
flows from the sampler head are equal and opposite and form a closed loop, so
that
vapors or particles not trapped in the sampler head are recirculated and
accumulate in the
loop. In a preferred embodiment, the jet pulse out-flow is powered by an
independent
pressure source and is exceeded by the suction in-flow to achieve a net
positive sampling,
such as when a millisecond sampling pulse out-flow is followed by a suction in-
flow of
longer duration to ensure that the sampled air volume is greater than volume
of the pulsed
air jet:
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V(SUCTION) > V(JET PULSE)
In practice, it has proved useful to operate the gas jets in single pulse mode
or pulse train
mode while under continuous or semi-continuous suction. In single pulse mode,
the gas
jets fire as a short burst after first activating the suction intake. In pulse
train mode, a
series of short bursts are emitted from the gas jets while operating the
suction intake. A
surface, substrate or object may be sampled with a single pulse or with a
series of pulses.
The sampler head may be moved or stationary between pulses, or a series of
pulses may
be emitted while the sampler head is moving and suction is engaged.
In another sampling system, the array of interrogation jet nozzles is
surrounded by a
perimeter of circumferential slits that emit a curtain wall of lower velocity
gas forming a
virtual shroud, skirt or apron around the virtual cone of the higher velocity
convergent
jets. This air is conveniently supplied by the exhaust of the suction intake.
The exhaust
of a blower used to power the suction intake, for example, may also be used to
provide
the gas flow for the curtain wall.
In yet another aspect, the invention is a method for sampling a residue from
an exterior
surface of an object, structure or person, which comprises contacting a
virtual sampling
chamber as described herein with an exterior surface at a distance less than
the height D,
of the virtual cone, whereby residues dislodged from the external surface by
the gas jets
are swept into a sampling return stream by the suction intake. The virtual
sampling
chamber may be employed intermittently with triggering, or cyclically, or
continuously,
but is preferentially pulsed with a pulse interval selected so that the jet
pulse volume may
efficiently be aspirated before firing a second pulse.
In a preferred aspect, one approach to a pneumatic sampler head combines
biomimetic
"sniffing" and interrogation jets for aerosolizing particles and optionally
vapors, the
combination serving as an efficient front end particle and/or vapor residue
concentrator
and capture device for use with a variety of analytical tools and instruments.
With respect to explosives surveillance and detection, the invention is an
apparatus for
concentration and collection of samples of explosives and explosives-
associated materials
for analysis, the samples having a particle fraction (including any adsorbed
vapors) and a
free vapor fraction. The apparatus comprises a) a sampler head with
directional nose, the
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nose having an intake port and upstream channel for receiving a first sample
as a suction
gas flow having a volume and a velocity and conveying the suction gas flow to
an air-to-
air particle concentrator, the air-to-air particle concentrator for
accelerating and inertially
dividing the suction gas flow according to a flow split into a particle-
enriched flow in a
first downstream channel and a bulk flow in a second downstream channel; b) a
particle
trap disposed in the first downstream channel for immobilizingly accumulating
particles
from the particle-enriched flow; c) a vapor trap disposed in the second
downstream
channel for immobilizingly accumulating free vapors from the bulk flow; d) a
means for
stripping a first constituent from a particle fraction in the particle trap
and an independent
means for stripping a second constituent from a vapor fraction in the vapor
trap, and
optionally e) a means for detecting a first signal from the accumulated
particles and a
means for detecting a second signal from the accumulated vapors so as to
detect an
explosive or explosive associated material in the first sample by integrating
or comparing
the first and the second signal. The apparatus enables independently detecting
a first
signal from a particle constituent and a second signal from a vapor
constituent and
integrating or comparing the signals to detect an explosive or explosive
associated
material in the sample.
Certain improvements in performance are made possible by use of the air-to-air
concentrator. Losses of particles in the size range of 5 to 200 microns are
reduced by
shunting the bulk flow around the particle trap. Particle fouling of the vapor
trap is
reduced by adjusting the cut size of a virtual impactor or particle separator
to 5 to 10
microns, resulting in cleaner signals in the vapor channel detector.
Systems having on-board means for analyzing particle and vapor constituents*
are termed
"fully integrated systems" and may be differentiated from systems for
interfacing with
remote analytical instrumentation, for example those systems where an
insertable
cartridge containing the immobilized samples of particle and vapor are
conveyed to a
stand-alone analytical instrument for analysis.
The air-to-air particle concentrator may be an aerodynamic lens with skimmer,
an inlet
particle separator with splitter, a vortex particle separator with particle
diverter, or an
elutriative particle separator with particle diverter. The air-to-air
concentrator preferably
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includes at least one aerodynamic lens or lens array disposed in the upstream
channel and
fluidly connected to the skimmer. The skimmer typically includes an inlet for
receiving a
particle beam or ribbon from the aerodynamic lens element, and splits the gas
stream so
that a bulk flow is diverted to a lateral flow channel and a particle-enriched
flow is
directed to a collector duct for particle capture and analysis. The skimmer is
provided
with a skimmer body, a skimmer nose, a lateral flow channel for receiving the
bulk flow,
and a virtual impactor mouth in fluid communication with a collector duct for
receiving
the particle-enriched flow. A particle trap is disposed in the collector duct.
The particle trap is typically mounted proximate to and downstream from the
skimmer in
the collector duct, and may be incorporated in the skimmer body. The skimmer
body
optionally is provided with a heating means for heating the particle trap. The
particle trap
may be a centrifugal impactor, a pervious screen, a bluff body impactor, or an
electrostatic precipitator. The pervious screen may be selected from a ceramic
filter or
mesh, a glass filter or mesh, a plastic filter or mesh, or a metal filter or
mesh. The vapor
trap is generally a sorbent bed or film or a carbon bed or film, but may also
be a liquid.
Means for stripping the particle constituent or constituents for analysis from
materials
accumulated in the particle trap include: a) injecting or circulating a volume
of a hot
carrier gas through the particle trap; b) directing an infrared emission, a
microwave
emission, or a laser emission at a particle in the particle trap; c)
resistively heating the
particle trap; d) injecting a solvent or solvent vapor; or e) any combination
of one or more
of the above means for analyzing the particle constituent or constituents.
Means for
stripping and analyzing the free vapor constituent or constituents may
include: a)
injecting or circulating a volume of a hot carrier gas through the vapor trap;
b) injecting
or circulating a solvent vapor in a carrier gas into the vapor trap; c)
directing an infrared
emission or a microwave emission at the vapor trap; d) resistively heating the
vapor trap;
or e) any combination of one or more of the above means for analyzing the free
vapor
constituent or constituents.
Means for detecting a particle or a free vapor constituent accumulated in one
of the traps
further generally comprise a) means for performing a liquid chromatographic
step; b)
means for performing a gas chromatographic step; c) means for performing an
affinity
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binding step; d) means for performing an ionization step; e) means for
performing an
electrophoretic step; f) means for performing a spectrometric, fluorometric,
or
photometric step; g) means for performing a mass spectroscopic step; h) a
means for
performing an electron capture step; i) means for in situ detection; j) a
combination of
one or more of the above means; or k) other analysis and detection means known
in the
art. Analysis means may be shared for particles and for vapors or may be
independent.
Optionally, particle constituents and vapor constituents may be pooled before
analysis.
Advantageously, independent capture of particle and vapor constituents from
separate
traps improves reliability and robustness of detection, reducing both false
positives and
false negatives. Using systems of the invention, constituents of the particle
trap and
constituents of the vapor trap may be stripped and analyzed (or analyzed and
stripped)
independently, so that analysis and regeneration conditions in each trap are
independently
optimized. Separate accumulation of free vapors trap yields cleaner vapor
signals when
present. Separate accumulation of particles is useful because stripping can be
performed
selectively, eluting selected classes of analytes in one or more solvents, for
example.
Solvent eluates can be flash evaporated to remove interferents from the
sample. Unstable
analytes can be subjected to liquid chromatography without thermal degradative
losses.
And those semi-volatile analytes that are difficult or impossible to detect as
free vapors
because of their low vapor pressure, can be analyzed without losses to
surfaces in the
sampling head.
Also included are methods for sampling particulate and vapor residues from an
object,
structure, surface, cavity, vehicle or person to detect an explosive. A method
may
comprise steps for a) aspirating a first sample having a volume and a velocity
into a
suction intake of a sampling head and conveying the volume as a suction gas
flow
through an upstream channel, the volume containing particles and free vapors;
b)
inertially dividing the suction gas flow into a particle-enriched gas flow
containing a
particle concentrate and a bulk gas flow containing the bulk of the free
vapors, and
directing, according to a flow split, the particle-enriched gas flow to a
first downstream
channel and the bulk flow to a second downstream channel, wherein the first
downstream
channel and the second downstream channel bifurcate from the upstream channel;
c)
immobilizingly accumulating any particles in a particle trap disposed in the
first
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downstream channel and any free vapors in a vapor trap disposed in the second
downstream channel; d) analyzing any constituents of the particles or free
vapors
accumulated in the traps to detect an explosive or explosive-associated
residue therein.
The step for analyzing may comprise eluting any constituents of interest in
the particle
trap in a liquid volume, optionally with heat, or volatilizing the
constituents in the particle
trap in a carrier gas volume, optionally with heat or solvent, or
alternatively, an in situ
analysis may be performed without elution or desorption of constituents. The
step for
analyzing also comprises desorbing any constituents of interest in the vapor
trap,
generally in a hot carrier gas volume, optionally with solvent vapor,
optionally with a
step for further concentration of the vapors in a secondary focusing trap, and
conveying
any desorbed constituents to a detector.
A step for cleardown of the sampling system between analyses may also be
provided.
Cleardown is achieved by convectively, conductively or irradiatively heating
the traps; by
injecting a purgative solvent; by purging the traps under a forward or reverse
flow of a
gas stream; by replacing the traps (as with a new or reconditions cartridge),
or a
combination of the above means.
Interchangeable sampler heads may be configured for sampling surfaces and also
for
interrogating spaces between surfaces, such as under pallets, between stacks
of articles,
inside vehicle compartments and trash cans, between boxes, in the nap or pile
of a rugs,
along floorboards, in bins of vegetables, and so forth, where we have found
that
combinations of jets with suction, can be optimized to improve overall
sampling
efficiency. Particulates are aerosolized by this treatment and entrained in
the suction
intake. Vapor recovery is improved by stripping any unstirred boundary layer
in the
sample area, such as is useful for detection of landmines. High velocity jets
also erode
contaminated substrates to yield additional analyte.
Sampler heads may be interfaced with particle and/or vapor collection and
analysis
systems for detection of trace residues associated with explosives and
explosives-
associated compounds, detection of landmines, particles associated with
biowarfare
agents, residues or particles associated with narcotrafficking, smuggling of
chemicals,
and animals or animal parts, environmental contamination of surfaces with
toxins,
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bacterial or other contamination in food processing facilities, bacteria,
fungi, viruses and
insects on agricultural and forest products, and so forth. These systems are
thus useful as
part of larger surveillance systems for surveillance of complex environments,
such as
traffic at a border crossing, flow of mail, monitoring of ecosystems, ingress
and egress of
persons to and from secure areas, and in forensic investigations, for example.
BRIEF DESCRIPTION OF THE DRAWINGS
The teachings of the present invention can be readily understood by
considering the
following detailed description in conjunction with the accompanying drawings,
in which:
FIGS. 1A and 1B are schematic views showing devices of the prior art.
FIG. 2A is schematic depiction of a sampler head in operation, the sampler
head having
six sampling jets surrounding a central intake port. A "virtual sampling
chamber" is
formed.
FIGS. 2B, 2C and 2D depict plan, section and elevation views of the six jet
sampler head
of FIG. 2A.
FIG. 3A is a computational model of a four jet virtual sampling chamber formed
by a
sampler head of a device of the invention. The lines represent streamlines of
air.
FIGS. 3B through 3D depict the footprint on the interrogated surface
established by
various configurations of jets, showing quad-, tri- and octa-jet
configurations.
FIG. 4 is a pictographic representation of the geometry of a virtual sampling
chamber.
FIG. 5 shows a detail of solenoid valve control of a gas interrogation jet in
a sampler
head.
FIG. 6 represents a pulse train of gas jets firing in synchrony.
FIG. 7 is a plot showing single pulse particle aspiration efficiency 71A as a
function of
pulse duration in an eight jet device.
FIG. 8 is a plot showing particle sampling efficiency rls as a function of jet
pulse
duration.
FIG. 9 is a pictogram depicting firing of an eight jet device.
13
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FIG. 10 is a plot showing gas jet velocity as a function of distance from
nozzle.
FIG. 11 is time lapse pictogram depicting re-aerosolization and entrainment of
particles
into a suction return stream following discharge of a gas jet pulse onto a
particle-coated
external surface.
FIG. 12 is a schematic of a closed-loop device for capturing particulate
residues from an
interrogated surface.
FIG. 13 is a schematic of a closed-loop device for capturing vapor residues
from an
interrogated surface.
FIG. 14 is a schematic of a representative closed-loop device for capturing
particulate
and vapor residues from an interrogated surface.
FIG. 15 is a schematic of an open-loop device with curtain wall for capturing
particulate
residues from an interrogated surface.
FIG. 16 is a schematic of a representative open-loop device with curtain wall
for
capturing vapor residues from an interrogated surface.
FIG. 17 is a schematic showing a device with aerodynamic lens and skimmer
integrated
into a sampler head.
FIG. 18 shows an aerodynamically contoured device in cross-section view with
annular
aerodynamic lens and skimmer integrated into the sampler head at the suction
intake.
FIG. 19 is a perspective view of the sampler head of FIG. 18.
FIG. 20 is a cutaway CAD view of a jet nozzle array with slit geometry.
FIG. 21A shows a portable sampling device in use. FIG. 21B is a detail of ajet-
suction
sampling nose.
FIG. 22 is a schematic of system flows for sampling particles and vapors using
a jet-
suction sampler head with flow split.
FIG. 23 depicts timing cycle considerations for a particle and vapor sampling.
FIGS. 24A, 24B and 24C are schematic views illustrating cyclical operation of
an
integrated particle and vapor collection apparatus with steps for sampling and
analyzing
14
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both particles and vapors, and then regenerating the particle and vapor traps
before
beginning a new cycle.
FIG. 25 tabulates vapor pressures of selected explosives and explosives-
associated
materials.
FIG. 26 is a plot showing a relationship between mass and aerodynamic size for
crystalline residues of TNT in a fingerprint.
FIG. 27A is a pictograph of a vapor trap with sorbent bed showing resin beads
and a coin
for size comparison. FIGS. 27B and 27C show a vapor trap assembly with
exploded
view.
FIG. 28 is a plot of breakthrough time for DMDNB vapors in a vapor trap.
FIGS. 29A and 29B are plan and cross-sectional views of a sampler body with
paired jets
and solenoids, a particle concentrator, and having a particle trap and
downstream vapor
trap for collection and analysis of explosives.
FIG. 30 is an exploded view of a first interchangeable "cartridge-type"
particle trap.
FIG. 31 is a plot of experimental data for jet aerosolization of selected
solid explosives
residues from a surface.
FIG. 32 depicts the effect of mesh configuration on particle capture
efficiency for the
particle trap of FIG. 35.
FIG. 33 is a plot of capture efficiency versus particle diameter for a sampler
head in a
vertical (solid line) versus a horizontal position (dashed line) and
demonstrates settling
effects on capture efficiency.
FIG. 34 plots optimization studies of jet diameter versus capture efficiency
for
explosives residues from a solid surface.
FIGS. 35A and 35B show data for jet aerosolization of water from a wet
surface.
FIG. 36 is a view of a portable sampler head with three interchangeable noses.
FIG. 37 shows a first interchangeable head configured as a widemouth surface
sampler.
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FIG. 38A depicts a second sampler head configured as a surface and crevice
sampler
with paired directional jets. FIG. 38B is a plan view of a spinning sampler
head with
propulsive jet nozzles.
FIGS. 39A and 39B are perspective and exploded views of a spinning jet nozzle.
FIG. 40 depicts a sampler head with slit-type virtual impactor.
FIGS. 41A and 41B are schematics demonstrating operation of a rotatable
valveless
particle trap with injection ducts for selectively eluting or vaporizing
captured particles in
a small volume.
FIG. 42 depicts a particle concentrator assembly with centrifugal particle
trap.
FIGS. 43A and 43B are schematics demonstrating operation of a rotatable
valveless
centrifugal particle trap.
FIGS. 44A and 44B are schematics demonstrating operation of a reciprocating
valveless
particle trap.
FIG. 45 is a sketch of a second insertable cartridge for particle collection.
FIG. 46 tabulates explosives detection over a range of expected analytes using
a dual
channel system of the invention.
FIG. 47 is a schematic view depicting implementation of a sampling device for
automated inspection of parcels.
FIG. 48 is a schematic view depicting deployment of a sampling device array
for
inspection of vehicles.
DETAILED DESCRIPTION
Although the following detailed description contains many specific details for
the
purposes of illustration, one of skill in the art will appreciate that many
variations,
substitutions and alterations to the following details are within the scope of
the invention.
Accordingly, the exemplary embodiments of the invention described below are
set forth
without any loss of generality to, and without imposing limitations upon, the
claimed
invention.
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The invention has applications for surveillance and analysis of particulates
and volatile
residues borne upon persons, articles of clothing, interior or exterior
surfaces of
buildings, furnishings, vehicles, baggage, packages, mail, and so forth. The
following
definitions are provided for convenience.
"Particles" include dust, droplets, mists, explosives residues, chemical
agents, biological
particulate agents, and toxins, while not limited thereto, and are generally
smaller than
grains of sand. Before or during sampling, particles may form "agglomerates"
that have
aerosolization and settling characteristics distinct from the particles
themselves. Of
particular interest are particles in the range of 1 to 200 microns, more
preferentially 5 to
100 microns, where most of the mass is generally found. Adsorbed vapors are
frequently
found as constituents of particles, including particles such as fibers, dust,
soil, clay, hairs,
skin cells, mists and so forth. Constituents of particles include analytes of
interest,
interferents, and matrix materials.
The terms "mobilization", "re-suspension", "aerosolization", and "re-
aerosolization",
refer to a phenomenon in which particles, initially resting on a surface (or
"substrate"),
are advectively entrained in a moving gas volume in contact with the surface.
As use here, particle "aerosolization" can also involve erosion of surfaces
such as
cardboard, cloth, packing materials, paint, and standing water on surfaces,
through the
action of aggressive gas jets.
When the term, "air" is used, included as well for the purposes of the present
disclosure
are other gases and mixtures of gas more generally that may contain particles
or vapors in
dilute concentrations. For convenience, "air" includes all such gases to the
extent that
they act as diluents and carriers for target analytes, particles, volatiles,
and vapors alike.
"Particle concentrators" include air-to-air concentrators generally, including
aerodynamic
lens particle concentrators, aerodynamic lens array concentrators, and micro-
aerodynamic
lens array concentrators when used in conjunction with a virtual impactor,
skimmer or
other means for inertially separating a gas flow into a particle-enriched flow
(also termed
"minor flow" or "scavenger flow") and a "bulk flow". Also included are cyclone
separators, ultrasound concentrators, inlet particle separators, and vortex
particle
separators. Air-to-air concentrators split an intake flow into two downstream
branches at
17
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a bifurcation, where the bifurcation may be a "skimmer", a virtual impactor, a
"splitter",
a simple "tee", or a particle diverter. The ratio of particle-enriched flow
rate to bulk flow
rate is determined according to a flow split, which is a function of the
pressure drop in
each of the two downstream arms, the cross-sectional area, and any resistance
related to
C,,. The particle-enriched gas stream, also sometimes termed a "particle beam"
or a
"particle ribbon" is delivered to an outlet of the particle concentrator or
module and may
be conveyed to an aerosol collector module (or "particle trap", see below).
The "cut
size" refers to the size of particles that are captured in the particle beam
or ribbon, and is
generally taken as the apparent aerodynamic size or diameter (D50) for which
50% of the
particles are captured.
"Aerodynamic focusing" refers to systems for forming generally collimated
beams or
ribbons of particles in a flowing gas stream. The systems contain three
elements: an
intake orifice for receiving a flowing gas stream, one or more focusing lenses
disposed
along the long axis of the gas stream, and an acceleration nozzle downstream
from the
aerodynamic lens or lenses. Aerodynamic lenses are constrictions in a channel
that create
converging and diverging flow accelerations and decelerations through which
particle
tracks converge by inertia on the center axis of flow, thereby depleting the
surrounding
gas streamlines of their particle content. Aerodynamic lenses may be of "slit"
geometry
or of "annular" geometry. Aerodynamic lens or lenses may also be disposed as
arrays as
described in US Pat. No. 7,704,294 to Ariessohn, which is co-assigned.
"Skimmers" refer to systems for splitting a flowing gas stream at a junction
so that a bulk
flow and a particle-enriched flow are directed into separate, bifurcating
downstream
channels. Generally a "virtual impactor" is positioned to receive the minor
flow in a
collector duct. Skimmers are described for example in US Pat. No. 7,875,095 to
Ariessohn, which is co-assigned. Skimmers are related to particle splitters
and particle
diverters more generally, all operating by similar principles of inertia.
"Inlet particle separators" also use inertia to separate particles from
surrounding gas in a
moving stream. Air entering through an intake manifold is accelerated and then
bent
sharply. Clean, particle-depleted air flows around the bend, but particles
having inertial
mass are not deflected with the streamlines and are captured by a splitter
lip, continuing
18
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into a "scavenger" bypass channel. The terminology may also refer to an outer
bypass
stream (herein a "particle-enriched flow") and a "core engine stream" (here a
"particle-
depleted bulk flow"). Inlet particle separators may be operated under vaneless
conditions
equivalent to slot-type aerodynamic lens geometry, or under swirl conditions,
where
vanes are used to generate a vortex-like flow regime in a cylindrical channel
that forces
particles to the outer wall of the channel, under and outside an annular
splitter lip, and
into a particle diverter duct. Clean air at the centerline of the vortex
enters a downstream
recovery manifold over and into the annular splitter, which can be modeled as
an airfoil.
"Particle traps" or "particle collectors" include inertial impactors broadly,
particularly
centrifugal impactors, and also bluff body impactors and fine meshes or
filters capable of
capturing particles in a targeted size range. Special classes of impactors
include liquid
impingers and plate impactors. Also included are wetted wall impactors and
rotary vane
impactors. Filters for particle removal include membrane filters, depth
filters, felts,
mesh, mesh layers, and beds, also termed generally, "barrier filters". Also
included are
elutriative particle collectors. Particle collectors are described in US Pat.
Appl. Nos.
12/364672 (titled "Aerosol Collection and Microdroplet Delivery for Analysis")
and
12/833665 (titled "Progressive Cut-Size Particle Trap and Aerosol Collection
Apparatus"), which are coassigned and are hereby incorporated in full by
reference.
Sensitivity of a trap is in part a function of preconcentration factor PF:
PF=Cf/C0
where Co is the initial concentration of an analyte in a sample and Cf is the
post-collection
and processing concentration. This experimental ratio may also be used to
account for
material lost in the trap during desorption.
"Stripping" refers to a process of removing captured materials from a particle
trap, as in
preparation for analysis or as in regenerating the trap for a next sample.
Stripping may be
performed with a combination of heat, solvent, gas, or solvent vapor, in
combination with
ultrasound, for example, and may involve selective extraction of constituents
that are
analytes of interest, interferents or matrix materials.
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"Explosives residues" include 2,4,6-trinitrotoluene (TNT), nitroglycerin (NG),
dinitroglycerin (DNG), ethylene glycol dinitrate (EGDN), cyclonite or hexogen
(hexahydro-1,3,5-trinitro-1,3,5-triazine, RDX), octogen (HMX), pentaerythritol
tetranitrate (PETN), dipicramide (DIPAM), ethylenedinitramine (EDNA), 1,3,5-
triamino-
2,4,6-trinitrobenzene (TATB), triacetone triperoxide (TATP), acetone
peroxide/nitrocellulose (APNC), hexamethylene triperoxide diamine (HMTD),
tetryl,
ammonium nitrate, urea nitrate, ANFO (ammonium nitrate/fuel oil mixtures),
plasticized
blends of cyclomethylenetrinitramine (RDX) and PETN (such as Semtex), other
polymer
bonded explosives (PBX), for example, while not limited thereto. Explosives-
associated
compounds more generally, particularly volatile molecular analyte species such
as
ethylene glycol dinitrate (EGDN), dimethyldinitrobutane (DMDNB),
mononitroluene, or
isotopically labeled explosives used for "tagging" commercial explosives as a
means of
source identification, are also of use for detection [Steinfeld JI and J
Wormhoudt. 1998.
Explosives detection: a challenge for physical chemistry. Ann Rev Phys 49:203-
32;
Singh S. 2007. Sensors - an effective approach for the detection of
explosives. J
Hazardous Matl 1-2:15-28]. Dogs are very sensitive to DMDNB and can detect as
little
as 0.5 parts per billion in the air. Also of interest as targets for detection
are those agents
identified and listed by the Bureau of Alcohol, Tobacco and Firearms as
explosives under
section 841(d) of Title 18, USC. Firearms residues, both before and after
ignition, may
also be encountered.
Referring now to the figures, a conventional vacuum sampling device (1) with
intake (2)
is shown schematically in FIG. IA. Under influence of suction pressure applied
to the
intake, flow streamlines (3) enter the intake port from the sides, sweeping
across a
proximate external surface (4) and picking up loose particles, but the devices
have a
reduced sensitivity due to dilution with ambient air and are relatively
ineffective in
mobilizing, eroding and aerosolizing particles. A device of this type is
depicted in US
Pat. No. 3,748,905 to Zahlava. Also relevant is US Pat. No. 5,476,794 to
O'Brien.
As described in US Pat. Nos. 6,861,646 and 6,828,795, application of a
cyclonic outer
flow regime is reported to improve the ability to sample complex surfaces at a
distance
from the detector head. This is shown schematically in FIG. 1B. A blower (6)
powers
outflow of cyclonic streamlines (9) through lateral port (8) in housing (7). A
bonnet (10)
CA 02742633 2011-06-08
is used to shape the cyclone. A central vacuum intake (13) with lip 12 draws
air from the
base of the cyclone. Inflow streamlines (11) are seen to rise into the vacuum
intake. An
external surface (4) is shown to be swept by the cyclonic streamlines (9) and
dislodged
materials are entrained in the returning gas flow (11). Optionally a photon
beam is used
to generate heated vapors from a surface, which are detected by ion mobility
spectroscopy. The device is reported to have an effective distance of up to 10
cm from
the nozzle (US Pat. No. 6,828,795, Fig. 9). Because the cyclonic streamlines
(9) engage
the external surface (4) at an essentially zero incidence angle, particle
rolling is favored
over particle detachment, limiting effectiveness in mobilizing, eroding and
aerosolizing
particles.
Contrastingly, we have directed sonic jet pulses or streams converging toward
a virtual
apex of a cone behind the surface to be interrogated without cyclonic flow.
Cyclonic
flow of the incident air stream is not believed relevant to the operation of
our invention.
We have found that for particle removal the impingement or incidence angle of
a jet
streamline, i.e. the angle of the streamline relative to a flat surface
generally parallel to
the sampler head, exhibits improved dislodgement and aspiration efficiency at
an
incidence angle of about 60 to 85 degrees (i.e., where 90 degrees is
perpendicular).
FIG. 2A depicts a "virtual sampling chamber" (250) formed of six jets of air
emitted
from sampling nozzles arrayed around a generally central suction intake port.
The
sampling jets are directed to form the walls of a virtual cone, shown here
converging on
an interrogated surface (4). When incident against the interrogated surface,
the jets
involute and are borne into the central collector duct in the sampler head. In
this way,
particles or vapors dislodged or volatilized from the interrogated surface are
entrained in
the returning flow and enter the suction intake port for concentration and
analysis.
In more detail, for a first embodiment (200) of the invention, sampler head
(210) has a
forward face (211) and a ring of jet nozzles (212) mounted in a
circumferential array
around a central axis (214). At the center of the forward face is a suction
intake port
(213) with conical inlet. Sampling jets (220) propelled from the jet nozzles
(212) are
directed to converge on an external surface (4), forming the walls of a
truncated virtual
cone. On striking the surface, the jets are turned inward and are returned
under suction to
21
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the suction intake port (213). Suction is generated by a vacuum pump (or
blower inlet)
mounted in or connected to the sampler head. A bundled core of suction return
streamlines (230) is shown at the central long axis of what is a "virtual
sampling
chamber" (250), the virtual sampling chamber having a truncated conical shape
with base
formed by the forward face (211) of the sampler head and frustrum by out-flow
streamlines making an involuted frustroconical "U" turn (221) on the
interrogation
surface (4). The out-flowing gas jets (220) are connected with the bundled
core of in-
flowing return streamlines (230) directed into the suction intake by the
frustroconical "U-
turn" of the streamlines at the surface.
Also shown is a positive pressure source (240), here a diaphragm pump, for
charging the
gas jets and tubulation (246) for discharging a curtain wall flow through
annular slit
orifices (245) disposed as an apron around the sampler head, as will be
discussed further
below.
The geometry of the conical "virtual sampling chamber" is illustrated
schematically in
FIG. 4. The virtual cone geometry (351) includes base (352), with central long
axis
(214), walls (353), apex or vertex (360), and frustrum (354). The walls of the
virtual
sampling chamber are formed by jets (220) flowing down the outside walls of a
cone
from the base to the apex. Returning flow (230) is formed by involution of the
jets (220)
where the cone is truncated on the frustrum. While not bound by abstract
models, the
returning flow is visualized as a cylinder (355) of negative pressure having a
base (356)
at the core of-and disposed on the long axis of-the virtual cone. An involuted
frustroconical "U-turn" of the gas flow streamlines fluidly joins the gas jets
(220) to the
sampling return stream (230). The number of jets forming the virtual sampling
chamber
may be two, three, four, six, eight, or more, while not limited thereto. By
shaping the jet
streamlines (220) in fan or chisel shapes, a virtual cone or pyramid is
readily formed with
as few as two shaped jets.
As discussed further below, the sampling jets may be emitted as a single pulse
or pulsed
burst, and after an interval of a few microseconds, the emitted gas volume is
efficiently
recovered by application of a strong suction pulse. Thus it can be seen that
the gas-
walled sampling chamber is formed and then collapses-truly an evanescent
22
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manifestation of a virtual sampling chamber having a duty cycle of a few
seconds, while
not limited thereto. Individual pulse cycles may be repeated at defined pulse
intervals, or
in response to a triggering event.
Although not shown, the source of pressurized gas for the sampling jets and
vacuum for
the suction intake may include centrifugal, rotary vane, piston, or diaphragm
pumps, or
other pumps as known in the art. The exhaust of the suction gas generator may
be used
to drive the gas jets of the out-flow. A high pressure tank of a gas or
pressure reservoir
may be charged to a pressure setpoint and gas released using high-speed
solenoid valves
to generate sampling jet pulses. Pressurized gas may be stored in tabulations
(such as
elastic hoses) within the sampler head. An outermost peripheral annular
curtain wall
flow may also be used to further enclose the virtual sampling chamber, as will
be
described below.
Average jet flow velocities in the range of 20 to 300 m/s have been found
useful in
studies performed to date. The calculated average jet velocity at the outlet
of a nozzle for
smaller diameter nozzles approaches 300 m/s, which indicates that the velocity
at the
nozzle center line is sonic, and that it operates at choked conditions with
higher than
ambient air density. Supersonic jets may also be used. Modeling studies by
computational fluid dynamics show that jet velocities and suction pressure
diminish over
distance from the sampling nozzle, but are capable of forming a virtual
sampling chamber
enclosing a distance Df of up to about 12 inches or more from the interrogated
surface,
where the distance Df is the height of a frustrum of a virtual cone as
measured from its
base (FIG. 4). In operation, the height of the virtual cone from base to apex
is D, the
virtual frustrum is formed with a height Df, where the height Df is less than
D, The
distance D.f may be 1 inch, 3 inches, 6 inches, 12 inches, or as found
suitable for
particular applications, according to the power of the jet pulses or streams.
Practical illustrations of the force of the jets in eroding residues from
surfaces and
forming aerosols are seen in FIGS. 11 and 39, where dry residues and liquid
water are
aerosolized.
The apex angle "theta" (or "vertex angle") of convergence of the jets forming
the virtual
cone may be varied as desired, but is found to be more effective in the range
of 10 to 60
23
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degrees, most preferably about 15 degrees. For a jet, the incidence angle is
the external
angle of the half angle of theta (359) and is 90 degrees for a jet normal to a
surface.
Incidence angle of a jet pulse is most effective in the range of 60 - 85
degrees. In some
applications, in order to increase the standoff distance Dc, it may be
desirable to use a jet
that approaches normal (perpendicular) to the forward face of the sampler
head. Instead
of a virtual cone, a virtual sampling chamber that is generally cylindrical
can be formed
when the jets are essentially parallel in trajectory.
FIG. 2B is a face view of the underside of a sampler head (200), termed herein
the
forward face (210). In this view, the forward face is generally round, but is
not limited
thereto. Depicted are peripherally disposed gas jet nozzles (212) and annular
slits (245)
used for curtain wall flow. Within the bell of the sample intake port (213,
FIG. 2C), is a
suction inlet (216) which is ducted to a suction pressure source (not shown).
Also shown
is the cross-sectional plane of the view of the sampler head of FIG. 2C.
FIG. 2C is a cross-sectional view of sampler head (200). The suction intake
port (213) is
depicted as being conical, but is not limited thereto, and is shown here with
a threaded
suction inlet (216) for connecting to a negative pressure source. The central
inlet is
bounded by a plate for mounting the gas jet nozzles (212) represented by a
black arrow
(220) and containing the annular slits (246) use for curtain wall flow
represented by an
open arrow (249). Internal to the plate are distribution manifolds, a first
plenum (247) for
supplying pressurized gas to the jet nozzles (212) and a second plenum (248)
for
distributing make-up gas to the curtain wall slits (245). In this embodiment,
the curtain
wall flows (249) are supplied from a blower via tubulations (246a) and curtain
wall
plenum (248).
FIG. 2D depicts a corresponding elevation view. Shown is the conical shape of
the
suction intake port (213, external view), the flat forward face (211) of the
sampler head,
gas jets (212a,b) mounted in the forward face, tabulations for supplying
curtain wall flow
(249a,b,c), and a diaphragm pump (240) depicted earlier, which supplies
pressurized air
to the gas jet plenum (247) in this embodiment.
A computational fluid dynamics (CFD) model (300) of the pneumatic action of a
sampler
head with four jets (320a,b,c,d) is shown in FIG. 3A. With the exception of
suction
24
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intake port (313) and suction pressure source (310), the mechanics of the
device itself are
not shown so that the pneumatic streamlines can be more readily visualized.
The four
sampling jets are directed downward at a surface (4) so that the jets converge
slightly in
proximity to the surface. The out-flow jet streamlines (321) surround a
virtual sampling
chamber (350). A suction return stream (332, formed by bundled parallel in-
flow
streamlines 331) is shown directed upward within the core of the virtual
sampling
chamber. Out-flowing jet streamlines (321) bend at the bottom, involuting as a
frustroconical "U" shaped squarish toroid (333) where contacting the external
surface (4).
As shown by CFD, vortex cyclonic flow does not develop under these conditions.
FIGS.
3B through 3D represent figuratively the `footprint' of the jet out-flow
streamlines (321)
and suction in-flow streamlines (331) on an interrogated external surface for
three, four
and eight jet configurations.
The impingement or incidence angle of a linear streamline forming the walls of
a virtual
sampling chamber is most effective for residue dislodgement and aspiration at
about 5 to
30 degrees from normal (i.e. about 60 to 85 degrees from horizontal to the
surface),
which cannot be achieved in a cyclonic flow regime, where streamlines are
essentially
perpendicular to the bulk axis of flow and the impingement angle approaches
zero. At
lower impingement angles, rolling and sliding of particles is favored over
lift-off. The
higher impingement angle permits the use of higher intensity focused jets and
the
application of pulsatile sonic and supersonic flow regimes, which results in
lift-off and
removal of both particulate and volatile materials from irregular and complex
surfaces,
and in better re-aerosolization and aspiration efficiencies for particles.
Optionally, by balancing the "out-flow" of the jet nozzles and the "in-flow"
of the suction
intake, a closed loop may be formed in which sample residues are concentrated
over
multiple passes through a vapor or particle trap. The sampling device is
intended for
particle and vapor removal and for aspiration of dislodged particles and
vapors into the
sample head from surfaces or objects from a distance Df of up to about 1 foot,
for
example a vehicle driven between stanchions supporting sampling devices
directed at
intervals onto the surfaces of the vehicle (FIG. 48). The size and power of
the jets and
suction intake can be scaled for larger standoff distances if needed. In other
embodiments, an open-loop is formed by firing the jets from a pressurized
reservoir and
CA 02742633 2011-06-08
ducting the bulk flow of the sampling return stream through a blower and
filter to charge
a curtain wall flow.
While configurations with four jets, six jets and eight jets are shown, other
configurations
and numbers of jets are envisaged. In selected geometries, a three jet or a
two jet
sampler head, where the jets are fan shaped, is directed at a surface and a
mated central
suction intake is configured to capture materials ejected from the surface by
the
impinging jets, optionally with a curtain wall or apron of flowing air improve
containment. Other variants for establishing a virtual sampling chamber are
possible and
are not enumerated here.
FIG. 5 depicts a detail of solenoid valve control of a gas interrogation jet
in a sampler
head. Jet control assembly (370) includes solenoid valve (371), control wiring
not
shown), and jet gas supply duct (372) fluidly connected to the jet plenum
(247). Gas
supplied to the plenum is rapidly distributed through the plenum manifold to
all jet
nozzles in the array. The array of jet nozzles is fired in synchrony. A jet
pulse (220) is
schematically depicted exiting jet nozzle (212) mounted on the forward face
(211) of the
sampler head. Also shown is curtain wall plenum (248) and curtain wall orifice
(245).
The curtain wall may be operated continuously or operated intermittently under
solenoid
control.
FIG. 6 represents a pulse train of gas jets firing in synchrony over a period
of 5000
milliseconds. Each gas jet pulse (380) originates as a pressurized wave of gas
equilibrated through plenum (247) and discharged through an array of nozzles
(212). Gas
jet pulses are followed by a period of continued suction to capture materials
dispersed in
the virtual sampling chamber by virtue of the impact of the gas jet or shock
wave on the
external surface. During the suction part of the cycle, make up air may be
supplied from
the surrounding air column or from an optional curtain wall flow. While gas
jet flow
may be operated continuously, in practice this has not proved necessary, and
discontinuous application of jet pulses with a limited duty cycle is
advantageous. In one
method of practice of the invention, sampling jet pulses as fired as
synchronous pulses or
as a train of synchronous pulses having a pulse duration of less than or about
20
microseconds and a pulse interval of less than or about 200 microseconds,
thereby
26
CA 02742633 2011-06-08
intermittently forming a virtual sampling chamber on the surface of a surface
to be
interrogated for volatile residues or particulate matter.
The effect of pulse duration and pulse separation is analyzed in FIGS. 7 and
8.
Sampling efficiency may be viewed as an exercise in optimization of two
processes, the
process of entrainment of residues associated with the interrogated surface in
the gas
streamlines (i.e. the process of "removing" or "mobilizing" residues from a
surface) and
the process of capturing those vapors and particulate residues in the suction
intake
stream. The processes compete because excessive velocities of particles kicked
up by the
gas jets can propel them out of the sampling cone. Thus the overall sampling
efficiency
lis is approximated by the equation:
TS - I1R * iA,
where is is the product of two efficiencies, the removal efficiency r1R and
the aspiration
efficiency r1A.
In FIG. 7 the effect of pulse duration is shown to have a paradoxical effect
on particle
aspiration efficiency r1A of an eight jet sampler head. The upper curve
(dashed line)
shows the timecourse for particle capture following a single 10 ms jet pulse;
the lower
curve (dotted line) compares the timecourse for a single 100 ms pulse. With
longer pulse
duration, particle aspiration efficiency drops due to loss of particles from
the sampling
cone.
However, when corrected for removal efficiency, overall efficiency is shown in
FIG. 8,
where particle sampling efficiency is is plotted as a function of jet pulse
duration,
showing the combined contributions of the dislodgement process and the
aspiration
process. For each condition, suction flow is commenced before triggering of
the gas jet
pulse and is sustained after termination of the pulse. Thus pulse duration is
optimized by
supplying sufficient time for aggressive scouring of the surface but using a
minimal time
to avoid loss of agitated particles from the containment zone.
Supplemental means for dislodging particles and volatile residues in the
sampling cone
include pulsatile flow regimes as described by Ziskind (Gutfinger C and G
Ziskind, 1999,
Particle resuspension by air jets-application to clean rooms. J Aerosol Sci
30:S537-38;
27
CA 02742633 2011-06-08
Ziskind G et al, 2002, Experimental investigation of particle removal from
surfaces by
pulsed air jets. Aerosol Sci Tech 36:652-59), ionized plasmas directed through
the
sampling jets, liquid or solvent directed through the sampling jets, or shock
waves
directed from the sampler head. The gas in the loop may also be heated,
chilled or
humidified to improve performance, although caution is taken to avoid losses
of volatile
particles due to heating. If desired, the jet nozzle array maybe operated in
repetitive
pulse mode, for example for sampling of a continuously moving belt.
FIG. 9 visually depicts the dynamic action of the interrogation jets. An array
of eight jets
can be seen to fire in synchrony in this graphical illustration. The
appearance of the jets
is enhanced by the introduction of particles in the gas flows which appear as
the fine
white pixilation against a black background. The duration of the pulse is
about 20
milliseconds, during which high speed jet flow is clearly visible.
FIG. 10 is a plot of jet velocity versus distance from the nozzle orifice
under
experimental conditions. Velocities for a 3 mm and 2 mm diameter nozzle are
shown.
The jet flow velocities of the apparatus of FIG. 9 were measured by heated
wire
anemometry. The jets maintain a well defined linear core velocity for up to
twelve inches
away from the nozzle. Synchronous pulses having a centerline nozzle velocity
of about
Mach 0.3 are achieved. Supersonic pulses are also conceived. Flow rates of
200, 500,
800, 1000 sLpm or greater are achieved. Pulses of 5, 10, 15 or 20 ms duration
may be
actuated as frequently as every 20 ms if desired. Alternatively, pulses may be
actuated at
50, 200 or 1000 ms intervals, for example.
FIG. 11 is a time lapse view of a jet pulse/suction cycle. In this graphical
illustration, a
time lapse view of the action of the array of gas interrogation jets on a
field of particles
on a solid surface is shown. The stationary nozzles are visible at the top of
the image and
a thin horizontal line of the solid surface is visible at the bottom of the
image. Frames are
taken at 5, 7, 11, 16 and 26 milliseconds, as shown here from left to right,
where the
explosion of particle dust as the pulse propagates against the solid surface
is clearly
visible. In the later frames, a plume of particulate is seen to rise and be
channeled by a
suction pressure into the central collection intake at the top of the image.
28
CA 02742633 2011-06-08
FIG. 12 depicts a schematic of a particle sampling apparatus (400a) with
housing (401,
represented schematically), particle concentrator (460) and particle trap
(470). Gas
containing residues and aerosols is collected in the intake (431) routed to
the particle
concentrator. Aerodynamic lenses for example organize aerosols into a stream
consisting of a particle-depleted bulk flow and a particle-enriched flow,
which may be
separated by a skimmer into what are commonly termed the "minor flow" and the
"bulk
flow", where the bulk flow contains most of the particles exceeding a
particular cut size.
A flow split is established whereby part of the gas flow, the "minor flow"
(461) enriched
for particles, is directed to the particle collector or trap (470). The
particle-depleted
"bulk" or "major" flow (462) is diverted, typically by use of a skimmer, and
is ducted
instead directly to the suction pressure pump. All the gas exhausted from the
concentrator (462) and the gas exhausted from the particle trap (471) are
returned to a
common suction pressure source for recirculation through the sampler head. As
shown in
this example, the pressurized exhaust from the vacuum pump or blower (430) is
used to
drive sampling jets (420) forming the virtual sampling chamber (450).
Particles resident
on the interrogated surface (4) are dislodged and drawn into the sampler head.
Material
in the particle trap is periodically analyzed in situ by methods known in the
art, or
archived for example by removal of a filter cartridge for later analysis by
chemical,
biochemical or physical methods. Separate pumps may be used for out-flow and
suction
in-flows if asymmetric flow rates are desired. Gas flows may be filtered or
purified
before re-use if desired.
An apparatus with one or more combinations of particle and/or vapor analytical
capability is also envisaged. Detection means for analysis and identification
of particles
or vapors are known in the art and may be selected for physical, chemical or
biological
analysis.
FIG. 13 depicts a schematic for one embodiment (400b) of a vapor sampling
apparatus
with vapor trap (490), vapor trap return flow (491), and housing (401). As
shown, a
virtual sampling chamber (450) is formed by gas jets (420) and a suction
return stream
(431) to the vapor trap. Vapor may be trapped, for example, as a condensate or
by solid
phase adsorption. A pump (430) recirculates the gas or air at the desired flow
rate, with
29
CA 02742633 2011-06-08
the linear velocity determined by the size of the jet orifices and the flow
rate. The
sampler head is held at a stand-off distance from the interrogated surface
(4). Material
collected in the vapor trap is periodically removed or volatilized for
analysis by methods
known in the art such as flash heating, ultrasound, or fast atom bombardment.
Known in
the art, for example, is the flash heater described by the Naval Research
Laboratory
[Voiculescu et al, 2006, Micropreconcentrator for Enhanced Trace Detection of
Explosives and Chemical Agents IEEE Sens. J. 6:1094-1104] and heating means
disclosed by Spangler in US Pat. No. 5,083,019, by Fite in US Pat. No.
5,142,143, by
Linker in US Pat. Nos. 6,345,545 and 7,299,711, and by Combes in US Pat. Appl.
Publ.
No. 2009/0211336. Also contemplated is the oxidative flash heater of
Pataschnick (US
Pat. No. 5110747). Included are flash bulb heaters, lasers, resistive heaters,
hot purge
gas, and microwave heaters as are generally known for heating.
Conceived is an apparatus combining functional elements for separating
particles and
vapors in an air-to-air concentrator followed by particle and vapor trapping
for analysis.
FIG. 14 is a schematic of an apparatus (400c) for capture of vapors and
particles.
Particles (and vapors associated with the particle fraction) are captured in
the particle trap
(470) and vapors that are conveyed by the particle concentrator (460) in the
bulk or
"major" flow (462) are captured in a vapor trap (490) before the gas (491) is
recycled
through vacuum/blower (430) and propulsed through the housing (401) as gas
jets (420)
into the virtual sampling chamber (450). Minor flow (461) from particle
concentrator
(460) is routed to the particle collector (470) and exhaust gas (471) is
recycled through
the vacuum/blower, essentially as a closed loop system, where there is a mass
balance
between jet in-flow gas and suction return stream (431) gas recovered from the
virtual
sampling chamber.
FIGS. 15 and 16 are schematics of pressurized pulse-driven devices (600a,b)
augmented
with curtain wall flow for capturing particles and/or vapors from an
interrogated surface
(4). In FIG. 15, the sampler head (601) comprises a suction pump/blower (680)
that
draws suction return flow (631) from a central collector duct through a
particle
concentrator module (660) and a particle trap (670) in series. Bulk or "major"
flow (662)
and minor flow exhaust (671) are recombined as a single stream (679) for
return to the
suction pump as make up air. The suction pump exhaust is ducted to slit
apertures on the
CA 02742633 2011-06-08
outer perimeter of the sampler head. The slit apertures form a peripheral
annulus outside
the array of jet nozzles on the forward face (611) of the sampler head (601).
These
outermost slit apertures generate a curtain wall of flow (681) that surrounds
and forms an
apron around the virtual sampling chamber (650). The virtual sampling chamber
is
formed by pulsatile jet flows (620) from a pressurized air source (630), here
shown as a
20 psig tank, although other pressures and pressure sources up to 60 or 100
psig have
been found to be useful. In this configuration, the virtual sampling chamber
is enclosed
in the peripheral flow of the curtain wall but the sampling jets are pulsatile
in nature.
Single pulses or trains of pulses may be used. Generally the curtain air is
continuously
ON while sampling is pulsatile, but other suction regimes may be useful.
FIG. 16 shows a corresponding sampler head (601) for collection of vapors,
where air
captured in the suction return flow (631) by the central collector duct is
passed through a
vapor trap (690) before being returned (691) to the suction/blower (680) and
exhausted as
curtain wall flow (681) through a peripherally disposed circumferential array
of slits. Jet
gas (620) is supplied from a pressurized tank (630).
FIG. 17 depicts a cross-sectional view of a combination "sniffer head" and
particle
concentration device with annular aerodynamic lenses (705,706). Unlike slit-
type
aerodynamic lenses, these lenses are cylindrical in cross-section. A curtain
wall flow
(681) from annular slit nozzles disposed on the forward face (611) of the
sampler head is
used to enclose a virtual sampling chamber. Interrogation jets (620) are fired
from
nozzles (613) as pulsatile flow at a surface beneath the sampler head (not
shown). Air
within the virtual sampling chamber is carried into a suction intake member
(701) so that
any entrained particulate or vapor material in the suction return stream (631)
is captured
and drawn under suction through a particle concentrator (760). The particle
concentrator
shown here is comprised of a two-stage aerodynamic lens assembly (705,706) and
a
virtual impactor (708, "skimmer"). Particle tracks (702) are shown to be
focused by the
aerodynamic lenses so as to form a particle-enriched flow (707) surrounded by
a particle-
depleted bulk flow. The core and sheath are separated in the skimmer: bulk
flow is
diverted as "bulk flow" (710) and the particle-enriched flow (707) continues
through
collector duct and exits the concentrator as the "minor flow" (709). The
degree of
concentration is determined by the flow split between bulk and minor flow. The
31
CA 02742633 2011-06-08
characteristics of the concentrator also determine a cut-size (as aerodynamic
diameter).
The configuration can be varied so that the cut size is in the range of 10
microns, 5
microns, or less, for example, as is useful for a variety of applications. The
minor stream
may be directed through a particle trap or filter cartridge (770), and the
exhaust is
recycled (723) through a suction/blower (not shown) and used to generate the
curtain
wall flow (681).
Surprisingly, one or more jet pulses of several milliseconds can be
superimposed on
curtain flow and suction cycles of one to several seconds, during which the
flow regime
conforms to the conditions required for use of stacked aerodynamic lenses as
shown.
FIG. 18 depicts a cross-sectional view of a combination sampler head and
particle
concentration device with suction intake having a generally conical geometry
(801). As
shown here, the intake bell receives a particle-loaded suction return flow and
focuses
particle tracks (802) in a pair of aerodynamic lenses (805,806). A virtual
impactor (808)
is used to separate minor flow (807) and bulk flow (809). Minor flow is
channeled to a
particle concentrator and then recombined with bulk flow for recycling to
curtain wall
flow (681). As described previously, the sniffer head consists of a forward
face (811)
with jet nozzles (812), annular slit nozzles (845) and a central suction
intake member
(801).
The virtual impactor (808) is comprised of a skimmer mouth (808a), a central
collector
duct (808b), a discoid chimney duct (808c) for routing the bulk flow (809) to
nipples
(808d) adapted, as shown here, for a hose connection to a vacuum source.
Aerosolized
particulate material is collected in a trap associated with the minor flow.
Explosives
materials for example are frequently crystalline or solid and are detected
when
aerosolized by a pressurized jet. Flow splits of greater than 100x are readily
achieved
with annular devices of this type, dramatically leveraging detection
sensitivity by several
orders of magnitude.
Multiple aerodynamic lenses may be used. For example by stacking four lenses,
concentration of particles over a broad range of particle sizes can be
achieved.
Beginning with the first lens, which acts on larger particles, the remaining
lenses in the
stack progressively act on smaller particles in steps of 2x to 4x. Thus by
example, a four
32
CA 02742633 2011-06-08
lens stacks may focus particles of 100, 30, 10, and 5 microns respectively,
while not
limited thereto.
In order to increase particle velocities in the central collector duct and
reduce elutriative
effects, the intake duct or "bell" geometry may be aerodynamically shaped to
minimize
particle impact, for example as per a NACA duct, Laval duct, elliptical duct
intake, bell
shaped duct intake, parabolic horn intake, exponential horn intake, quadratic
convergent
duct intake, power series convergent duct intake, or other tapered geometry of
the intake.
Fins or airfoils for minimizing turbulence, reducing deadspace and increasing
linear
velocities of the streamlines may also be used. As the lenses are improved by
contouring
to relieve eddy separation and particle wall impaction, performance is also
seen to
improve significantly, particularly in the collection of larger particles,
which
problematically are otherwise lost to sedimentation and rebound following wall
impaction in the sampler head and concentrator.
FIG. 19 is a CAD drawing of the combination sampler head and annular
aerodynamic
lens with skimmer assembly (810) of FIG. 18. The forward face (811) of the
intake bell
is pointed away from the viewer in this case so that the discoid skimmer
assembly (808)
is more clearly depicted. A central collector duct with skimmer mouth (808a)
and bulk
flow exhaust hose nipple (808d) are labeled. Also shown are mounting points on
the
lower sampler head for gas jet feed (814) and for a curtain air slot feed
(815).
Tubulations are not shown for simplicity.
FIG. 20 is a cutaway CAD view of a jet nozzle array with slit geometry. Here
the
architecture of the jet nozzles is modified and integrated into the material
of the sampler
head (850). The forward face (853) of the sampler head is configured for
emitting fan-
shaped jets (852) via a ring of slits (851a,b,c,d). Central suction intake
port (863) for
receiving sampling flow stream (862) is shown in cutaway view, where the front
half of
the sampler head is not shown.
Devices and systems of the invention have applications for sampling and
detection of
explosives residues. A wide range of analytes must be detected. Surveillance
systems
for selective sampling and detection of only a few explosives-associated
analytes or
families of analytes would have significant vulnerabilities. Nitro- and
nitrate-based
33
CA 02742633 2011-06-08
materials are the most numerous, but materials such as perchlorates,
peroxides, azides,
incendiaries, propellants, and hydrocarbons must also be considered. Mixtures
and
combinations, such as of fuel oil and ammonium nitrate, are also of interest.
Detection of
crystalline ammonium nitrate in combination with fuel oil vapor is
significantly more
conclusive than detection of either a nitrate (such as from a prescription
tablet) or a fuel
oil vapor (such as from dirty shoes) alone. Also of particular interest are
mixtures
including taggants and other explosives-associated materials (XAM) indicative
of
processed explosives.
Equilibrium vapor pressures of explosive materials range widely, from over 4.4
x 10-4
Torr for nitroglycerin (NG), 7.1 x 10-6 Torr for TNT, to 1.4 x 10-8 Torr for
PETN and 4.6
x 10-9 Torr for RDX at 25 C [Conrad FJ 1984 Nucl Mater Manag 13:212]. Also to
be
considered, however, is the affinity of the vapor molecules for solid
surfaces, which may
suppress free vapor concentrations, thus reducing detectable thresholds. We
find that
detection of volatile compounds such a dinitrotoluene, a degradant of TNT
which has an
affinity for solid surfaces, can be improved by collecting particles that have
equilibrated
with vapors of the explosive. These particles are typically endogenous
materials that are
exposed to the explosive residues in the environment, for example road dust,
silica,
ceramic, clay, squamous epithelial cells, hairs, fibers, and so forth. By
collection of
exogenous particulate materials, explosives residues associated with the
particulate debris
are found to be more reliably detected.
A sampling system for collection of particles and vapors is depicted
conceptually in FIG.
21A, which illustrates a wand-mounted sampling device 1000 as may be used in
sampling particles and vapors in an enclosed volume such as between two boxes
1001 or
other crevice, under a pallet, in a narrow pocket in an automobile trunk, a
space behind a
desk, and so forth, the space having a width and length greater than the
sampler head size
and a depth up to or significantly greater than the working length of the
wand.
The sampling device comprises a jet-suction head 1002 with a pair of forward
facing jet
nozzles 1003 and central suction intake 1004, a wand with handle and control
interface, a
suction blower 1005 for pulling a bulk flow, and internal pneumatics as
described
34
CA 02742633 2011-06-08
schematically in FIG. 22. A more detailed view of the nose of the sampler head
is shown
in FIG. 21B.
The internal workings of a wand or sampler head 1000 generally include (FIG.
22) a
particle trap 1006, a vapor trap 1007, a compressor 1008 and a pressure
reservoir 1009
for charging pressurized gas to operate a jet pulse system via distribution
manifold 1010,
solenoids lOl la,b for actuating jet pulses 1012a,b, a battery or other power
supply, a
suction blower 1005 for drawing a bulk flow through the vapor trap 1007, a
vacuum
pump 1013 for drawing a particle beam or ribbon through the particle trap
1006,
tubulation for the conveyance of gas flows, control circuitry 1019, and any
wiring
harnesses as needed for powering and controlling the device. The wand or
sampling
head also includes an air-to-air particle concentrator 1014, such as an
aerodynamic lens
(ADL) or lens array as is used to organize a gas intake stream 1015 into a
particle beam
or ribbon (comprising the particle-enriched flow, also sometimes termed a
"minor" flow
1016) and a bulk flow (also sometimes termed a "major flow" 1017) in
combination with
a skimmer (also sometimes termed a "virtual impactor" 1018). The skimmer may
be of
annular or of slit design. The bulk flow is particle-depleted due to the
inertial focusing
effect of the aerodynamic lens or lens array on particles and is separated
from the
particle-enriched flow in the skimmer according to a flow split. Inlet
particle separators
may also be used for separating a bulk flow from a particle-enriched flow
according to a
flow split. The systems are designed for combined particle and vapor sampling
system
with jet-suction sampling head.
Also provided are control circuits 1019 for powering and controlling operation
of the
apparatus. Control elements may include a microprocessor or microprocessors,
RAM
memory, complex logic instructions stored in non-volatile memory (such as
EEPROM),
optional firmware, and I/O systems with A/D conversion for collecting data and
D/A
conversion for transmitting instructions to analog subsystems such as pumps
and valves
and for controlling the flow of power to component systems of the pneumatics
and any
on-board analytic module(s). Logic circuits may be configured for comparing or
integrating detection signals from a particle channel and a vapor channel.
CA 02742633 2011-06-08
Three pumps are shown and arrows represent gas flows; black arrows indicating
positive
pressure, open arrows indicating suction pressure. System timing is provided
by a
controller 1019 which optionally also supplies power to the component
subsystems. For
purposes of illustration, only two jets and paired solenoids are shown. During
sampling,
jet pulse outflows from the nose of the device are deflected by collision with
an external
surface and are aspirated, at least in part, as a suction intake flow 1015
through a suction
intake in the forward face or "nose" of the sampling head and into the air-to-
air
concentrator 1014. A skimmer 1018 is used to separate the particle-enriched
flow 1016
and the particle-depleted bulk flow 1017 at a flow split that is determined by
the relative
capacity of suction blower 1005 used to pull the bulk flow and vacuum source
1013 used
to pull the particle ribbon or beam. The bulk flow contains the majority of
the free
vapors in the sample. The flow split between bulk flow and central core flow
is typically
configured to be greater than 50:1 and may approach or exceed 250:1. Pressure
drops on
the particle and vapor sides of the skimmer may be controlled separately.
Bulk flow 1017 is drawn through a vapor trap 1007 to capture any entrained
free vapors
of interest. The particle ribbon or beam flow 1016 is drawn through particle
trap 1006 to
capture any entrained particulate matter and adsorbed vapors. The particle and
vapor
constituents of the suction intake flow are thus not collected in series, but
are instead
separated so as to independently optimize their respective conditions for
accumulation,
extraction, and analysis.
Analytical systems may be supplied on board (not shown) or may be provided at
a remote
workstation. Thus the particle and vapor traps are optionally cartridges that
are placed in
the gas flows and removed for analysis. Optionally, the skimmer nose may also
be
supplied as part of the cartridge. In integrated systems, a common analytic
system may
be used to analyze both particle and vapor trap constituents; or the analytic
systems may
be independent.
The capacity of a representative suction blower 1005 is typically in the range
of 300 to
1500 liters/min at a suction head pressure of 5 inches of water, while not
limited thereto.
The required flow rates may be achieved with a centrifugal blower such as a
Windjammer Model 116630E or a 5.7" regenerative blower (AMTEK Part No. 116638-
36
CA 02742633 2011-06-08
08, Kent OH). The capacity is designed to be effective in aspiration of solid
from up to
about 1 foot (>30 cm) from the sampler head, typically with jet assist. For
portable
operation on DC power, a Microjammer 3.3" BLDC low-voltage blower (AMETEK Part
No. 119497) maybe used. Fans may also be used.
Particle ribbon or beam flow may be powered for example by a diaphragm vacuum
pump
1013 such as a BTC-IIS Vacuum Diaphragm Pump obtained from Parker-Hargraves
(Model No. C.1C60G1.1C60N1.A12VDC, Mooresville NC). Flow rate for the particle-
enriched flow downstream from the skimmer is typically in the range of 10 to
15 L/min
or less at a suction head pressure of about 20 to 30 inches of water.
Exhaust from the suction blower 1005 optionally may be used to power a curtain
air flow
through slits mounted peripherally on the sampler head, although not shown
here.
Jet pressure is provided by a compressor 1008, typically a diaphragm pump such
as a
Parker-Hargraves D737-23-01 double diaphragm pressure pump or a Thomas (Part
No.
11580C56, Sheboygan WI). Optionally, any 100 - 120 psi air pressure source
such as
compressed air can be used. Pressure is typically accumulated in a pressure
reservoir
1009, which may be a tubulation or an in-line tank and is distributed through
a manifold
1010 to an array of jets; the manifold is configured to equalize pressurized
gas feed to the
individual jets.
Solenoids 1011 include Gem Sensors (Plainville CT) Part Nos. B2017-V-VO-CI 11
with
a Cõ flow factor of 0.43 and 7 Watt coil; D2014-S89 (D2014-SB1-V-VO-CI 11)
with
0.21 C,, body and 10 Watt coil; and A2016-V-VO-C111 with 0.24 Cõ body and 6
Watt
coil operable at 100 psi. Also tested was an ASCO Part No. 8262H112 with a C,,
of 0.52
which is also available in DC configuration. These valves were selected for
their fast
reaction times in order to generate pulses of about 2 to 20 millisecond
duration. For
general purposes, a 10 ms pulse is useful.
Individual jet pulse outflows in the range of 5 to 20 ms duration have a
volume at STP of
about 2 to 6 cc3. Because jet arrays can contain multiple nozzles, total jet
volume is
typically a multiple of that, for example 12 to 36 cc3 for a 6 jet array. Jets
are typically
operated at choke or near-choke conditions, and at the nozzle, jet out-flow
linear velocity
approaches the supersonic threshold of 320 m/s. Pulses are thus pressurized at
up to
37
CA 02742633 2011-06-08
about 10 Atm or higher, typically at least 30 to 150 psi, and are
underexpanded when
released. Jet velocity stagnation (as measured by centerline velocity) is not
seen at
distances of up to 30 cm, as shown in FIG. 10 for a 3 mm and a 2 mm nozzle, so
that
particulate material can be mobilized and sampled at distances of up to a foot
from the
sampling nose.
Under choked flow conditions with fast valve actuation (solenoids 1011), jet
pulse 1012
energy may be varied by selecting nozzle size or critical dimension. Jet
nozzles may be
circular or may have asymmetrical shapes, such as fan or chisel shapes.
Nozzles may be
arranged in various configurations on the sampler head and the pulse volume
emitted by
each nozzle is generally summed to determine the total pulse volume. Jet
velocity at the
nozzle is graphed in FIG. 10 for selected nozzle diameters. Images of jet
pulse action on
a substrate at about 30 cm are presented in FIG. 11.
FIG. 23 demonstrates the sorts of pulse timing considerations that are useful
in jet-
assisted sampling and analysis. During an initial interval of time, which may
be 0.1 to
0.5 seconds, a suction regime 1021 is established by turning on suction blower
1005 and
diaphragm pump 1013. A jet flow 1022 of 2 to 20 milliseconds is then actuated,
the jet
out-flow being a smaller volume than the suction in-flow and typically of 5 to
20 ms in
duration. Not shown, trains of pulses may also be used. The jet flow is
directed from the
sampling head to disrupt parasitic aspiration in the manner of an air knife,
and to dislodge
and erode surfaces that it contacts. Multiple jets may converge on the surface
to be
sampled so as to form a virtual sampling chamber. Upon striking a surface, jet
energy is
deflected so that the jet volume and any entrained solids and/or vapors, at
least in part,
are more readily pulled into the suction intake. As the jet pulse dissipates
and loses
coherence, it is aspirated into the suction in-flow. Typically, suction for
one to ten
seconds is useful and sufficient for collecting any residues dislodged by the
jet pulse.
When larger surfaces are to be sampled, and sample materials are accumulated
for longer
periods of time, intermittent or trains of jet pulses may be applied.
Following jet-assisted suction aspiration, any analyte captured in the
particle trap is
stripped from the trap and conveyed 1023 to an analytic module. Analyte
captured in the
vapor trap is also stripped from the trap for 1024 for conveyance to an
analytic module.
38
CA 02742633 2011-06-08
Both traps will be pneumatically (or hydraulically) coupled so that a volume
of a carrier
gas (or liquid) can be passed through each trap, concentrating the analyte
from each trap
in a smaller volume for analysis. In the analytic module, analysis and
detection of any
signal from one or more constituents or analytes is by conventional means.
Optionally,
all or part of the volume from each trap may be directed to a focusing trap
for further
concentration before analysis or may be captured on a sorbent for archiving if
desired. In
situ detection technologies may also be used.
Once any entrapped analyte or analytes have been extracted, a purge step 1025
is initiated
so that the traps are regenerated in preparation for a second analytical
cycle. Where in
situ detection is practiced, negative samples are discarded without further
analysis and a
second cycle of jet-assisted suction may be initiated immediately.
Alternatively,
regeneration is accomplished by cartridge replacement. Stripping means are
useful to
extract "strippates" for analysis and also to purge the traps.
Thus a single analytical cycle may have a duration of a few seconds to perhaps
a minute.
First, a jet pulse or pulse burst is actuated to dislodge a sample, suction is
continued for
several seconds to a minute or more to aspirate the sample; the contents of
particle and
vapor traps are then examined, and the traps are then purged or replaced and
the
electronics cleared so that a next sampling cycle may be initiated with a
clean trap and no
alarms pending (the process of purging the traps and resetting the electronics
is termed
"cleardown").
Referring to FIGS. 24A, 24B, and 24C, shown are three schematics depicting the
stepwise, cyclical operation of an explosives vapor and particle detection
apparatus 1030
with particle and vapor traps operated in parallel downstream from a particle
concentrator. A sampling and detection cycle involves A) a sampling and
capture step,
B) an analysis and detection step, and C) a regeneration and cleardown step.
In a first step (FIG. 24A), jet out-flow 1012 and suction intake 1015 are
actuated by a
controller 1019 to mobilize and aspirate a sample stream into the jet/suction
nose at a
flow rate sufficient to prevent most particles in the 5 to 100 micron or even
200 micron
range from settling. The suction intake flow 1015 is focused and accelerated
before
splitting a bulk flow 1017 from a particle-enriched flow 1016 in a skimmer or
other air-
39
CA 02742633 2011-06-08
to-air particle concentrator (indicated by bifurcation in black arrows)
according to a flow
split. The bulk flow 1017 is directed through a vapor trap 1007 at low
pressure drop and
high throughput to more cleanly capture vapors; the particle concentrate 1016
is directed
through a particle trap 1006 at a higher pressure drop and lower throughput to
more
efficiently capture particles-generally the two downstream branches are under
the
control of independently operated pumps I and II. Captive particles accumulate
in the
particle trap; captive vapors accumulate in the vapor trap.
Analysis is then initiated. This process is depicted in FIG. 24B as an
independent
process for each trap. Because vapors will break through the vapor trap over
time (see
FIG. 25), the vapor trap is must be analyzed and regenerated from time to
time, or
replaced. Any constituents or analytes of interest in the traps are
transferred to an
analytic module 1031 or may be detected by in situ detection so as to avoid
unnecessarily
performing "in depth" analyses of negative samples.
The particle trap will typically contain explosives residues having higher
boiling points in
particulate form, whereas the vapor trap will contain lower boiling point
materials. Thus
the stripping operation and analytic module 1032 used with the particle trap
may be
operated independently or at different conditions than the stripping operation
and analytic
module 1031 used with the vapor trap. Because vapor-related and particle-
related
analytes frequently benefit from different analytical conditions, separately
optimized
analytic modules (1031, 1032) are shown. Stripping of low vapor pressure
explosives
from the particle trap for delivery to an analytic module, for example, is
more efficient
when performed by liquid elution rather than by evaporation, but stripping of
higher
vapor pressure analytes from the vapor trap is more efficiently performed
using thermal
desorption in most cases.
However, if desired, a single common analytic module may be used for both
channels,
either by performing sequential analysis or by pooling the particle and vapor
samples.
Particles can also carry adherent volatiles and themselves may be volatilized
in full or in
part by heat so that both the high boiling point volatiles and any associated
vapor
constituents associated with the particle concentrate may be analyzed
together.
CA 02742633 2011-06-08
Analysis generates detection signals, a first signal for any particle
constituent from the
particle trap and a second signal for any vapor constituent from the vapor
trap, if present.
The two signals may be integrated and/or compared for additional information
of use in
detection of explosives. Confirmatory information is obtained. Information is
also
obtained if an interferent disables one analysis channel but not the other.
Thus false
positives and false negatives are reduced. Particles can be associated with a
large amount
of interferents, but by adjusting the cut size to essentially eliminate
particle mass from the
vapor channel, very clean vapor signals result.
The analytic module or modules may contain hydraulics or pneumatics and one or
more
conventional means for detecting one or more analytes/constituents of
interest. The kinds
of analytical instruments that may be adapted for explosives detection from
particles and
vapors are those that are known in the art. The analytic module may also
contain
focusing traps which function essentially as second stage preconcentrators in
series with
the particle and/or vapor traps and may also be used to prepare samples for
archiving.
In a third stage of a sampling/analytical cycle, the particle trap 1006 and
vapor trap 1007
are regenerated if necessary as depicted in FIG. 24C, for example by heating.
In one
instance, the particle and vapor traps may be heated and flushed during
regeneration.
Ports to the analytic module and between the particle and vapor trap are
closed and the
pump exhausts are engaged so as to flow clean air through the sampler head,
preferably
in a reverse direction, clearing any volatiles and deposited materials from
the traps and
associated channels and internal surfaces of the device. Particle traps having
heat
resistant construction may be incinerated to ash common contaminants such as
dust or
cellulose fibers that would otherwise clog the trap. Liquid flush solutions
may also be
used. Embedded ultrasonic or microwave cleaning elements are also assistive in
clearing
the traps of any interferents before a next sample is collected. Electronics
are also reset
during cleardown.
There is a need for systems capable of detecting both particles and vapors,
yielding
complementary information. As can be seen from FIG. 25, vapor pressures for
explosives and explosives-associated materials vary over many orders of
magnitude.
Several important classes of high explosives and primary explosives, including
RDX,
41
CA 02742633 2011-06-08
HMX, PETN, TATP, and HMTD, may be missed when vapors alone are sampled. The
vapor pressures of RDX, HMX, PETN and other potential explosives are so low as
to be
below the limits of detection by ordinary means. Thus particle collection is
an essential
aspect of any explosives detection programme.
Conversely, certain explosives and explosives associated materials occur with
vapor
pressures in excess of parts per million and are relatively straightforward to
detect as free
vapor. They are sometimes smelled with the human nose and are targets for
canine
detection. These include nitroglycerin, fuel oil, ammonium nitrate, ANFO
mixtures, and
taggants, for example. Taggants have been proposed to facilitate detection of
low vapor
pressure explosives. Taggants include 2,3-dimethyl-2,3-dinitrobutane (DMDNB),
ethylene glycol dinitrate (EGDN), and 4-nitrotoluene (para-NT). These
compounds were
chosen because they do not occur in nature, they do not tightly adhere to
common
substrates, and because they continue to release their vapors for 5 to 10
years [J. Yinon.
1995. Forensic Applications of Mass Spectrometry, CRC Press, Boca Raton, FL].
Other
odiferous "fingerprint compounds" such as cyclohexanone (CXO-used in
recrystallization of RDX), benzoquinone, 2-ethyl hexanol (2-EH, used in
manufacture of
plasticizers), triacetin, and diphenylamine also may be present in significant
amounts for
detection [Williams et al, 1998, Canine detection odor signatures for
explosives, Proc
SPIE 35:291-301; WIPO Doc. No. 2010/095123]. These odor fingerprint compounds
can
be captured for example using gas phase SPME and detected by IMS [US Pat. Doc.
2009/0309016; Perr et al, 2005, Solid phase microextraction ion mobility
spectrometer
interface for explosive and taggant detection, J Sep Sci 28:177-183; Lai et
al, 2008,
Analysis of volatile components of drugs and explosives by solid phase
microextraction-
ion mobility spectrometry. J Sep Sci 31: 402-412]. However, taggants are
generally not
used by illicit explosives manufacturers and a negative vapor detection event
must always
be viewed with uncertainty.
Use of upstream air-to-air concentrators has unexpected benefits when both
particles and
vapors are to be detected. A synergy is achieved when the sample is split into
a particle-
rich fraction and a particle depleted fraction. When particles are directed to
a particle trap
and vapors are directed to a vapor trap downstream from an air-to-air particle
concentrator, the following benefits accrue:
42
CA 02742633 2011-06-08
A. Particle-enriched air is supplied to the particle trap at reduced volume,
typically
1/1001h or less of the suction intake volume, so that a particle trap with a
given cut
size may be smaller without an increase in pressure drop, resulting in more
efficient collection of particles at a higher preconcentration factor PF;
B. Particle-depleted air supplied to a downstream vapor trap results in less
fouling of
the vapor trap and a cleaner signal in the detector;
C. Because of the qualitative differences in the kinds of analytes that will
be directed
to the particle trap and the vapor trap, physical separation of the traps
permits
independent optimization of analyte stripping and analytical modalities, in
some
cases resulting in different and complementary information from each channel;
D. In the suction intake, elutriative losses of the most information-rich
particles
(from 5 to 200 microns in apparent aerodynamic diameter) are minimized because
the suction velocity can be higher, i.e., almost all of the airflow bypasses
the
higher pressure drop particle trap and hence the suction intake can be
operated at
a much higher throughput-while synergically decreasing the size of the
particle
trap so as to increase the preconcentration factor, a virtuous result and an
advance
in the art.
These synergies have not been anticipated in the art. The prior art taught
particle traps
having large surface areas and deadspace (generally employing a particle trap
to collect
both particles and vapors or a particle trap in series with a vapor trap). The
smaller the
particle to be collected, the larger the pressure drop per unit filter area,
and thus pressure
drop dictates the surface area-to-cut size ratio of particle filters. While it
would be useful
to sample hundreds of liters of air for trace vapors, passing such a volume of
air through a
fine particle filter would be prohibitive in a small unit. As shown here, use
of an in-line
air-to-air particle concentrator overcomes this problem. Air-to-air
concentrators may be
operated a flow split of 30:1, 50:1, 100:1 or even 250:1 and at particle cut
sizes (in the
concentrator) of 5 to 10 microns (or even 1 micron if desired), thus shunting
very large
amounts of particle-depleted air around the particle trap and permitting
miniaturization of
the particle trap. Happily, stripping operations for harvesting particle
constituents from a
43
CA 02742633 2011-06-08
very small particle trap can be conducted with a correspondingly small volume
of
stripping agent, with geometric increases in preconcentration factor and
sensitivity.
With air-to-air concentrators, operational systems have been achieved at more
than 1000
sLpm in portable units and are readily scaled for higher throughputs.
Miniaturization of
the particle trap increases detection sensitivity by increasing the
preconcentration factor;
the hollow trap volume of the particle traps (i.e., the deadspace volume of
the trap) may
be reduced to sub-milliliter dimensions in this way.
Correspondingly, very large quantities of air may be sampled for free vapors.
Particles
are not allowed to impact the vapor trap. Vapor trap signals are cleaner
without this
interference. As pointed out perhaps first by Corrigan (US Pat. No. 5,465,607,
Col 20
lines 3-14), semi-volatile materials can overwhelm and degrade performance of
GC/MS
and MS/MS instruments. Thus by freeing the vapor signal from particle-derived
interferents, more sensitive and refined analytical techniques may be applied.
Particles can rapidly foul vapor sorbent beds, poisoning the sorbent and
preventing
regeneration and cleardown. The excess heat required to fully bake off or
incinerate
particulates on a sorbent bed can exceed the thermal stability of the resin.
Sorbents are
likely to bleed particle-associated interferents for long periods of time,
degrading the
effectiveness of subsequent sampling.
The challenge for particle and vapor collection systems is made more difficult
because
sampling and detection conditions are not necessarily copacetic. Vapor analyte
stripping
from a vapor trap is inherently best performed by desorption, but stripping of
analytes
from a particle trap may be best performed with a solvent, for example.
Heating of
HMTD, for example, is likely to yield C02, ammonia and trimethylamine, but
with
solvent elution, intact HMTD will be recovered, greatly aiding interpretation
of the
resulting spectrograms. PETN has an extremely low vapor pressure, a tendency
to adhere
to surfaces, and is unstable at temperatures of even 100 C, making gas
chromatographic
detection difficult. Lower nitrate esters of pentaerythritol are more readily
detected under
conditions that would not favor vapor detection, such as with liquid
chromatography.
Conversely, DNT has a higher vapor pressure than TNT, and is a favored analyte
for
vapor detection, but TATP or EGDN would not likely be detected by thermal
desorption
44
CA 02742633 2011-06-08
under conditions suitable for desorbing DNT. Thus the use of a single
stripping
technique for both the vapor trap and the particle trap, as proposed by Syage
for example
in US Pat. No. 7,299,710, can result in significant blind spots in
surveillance.
Independent detection of the contents of vapor and particle traps can also
yield patterns
that are more definitive than single channel analysis. Given the significant
differences
between the kinds of materials likely to be directed to the particle trap
versus the vapor
trap, a physical separation of the two traps results in a unique opportunity
to apply
different analytical techniques to each.
Finally, by diverting the bulk flow to the vapor trap, higher velocities in
the suction
intake may be achieved. A lower pressure drop in the vapor trap is readily
achieved, and
higher flow rates more easily accommodated. By increasing velocity of the
suction
intake, particles that would otherwise settle out and be lost may be
successfully aspirated
with the sample. A single larger particle can have more informational value
than
thousands of liters of vapor. Because, as indicated by the data of FIG. 25,
collection of
vapors only can result in substantial blind spots in surveillance, any means
that results in
higher efficiency of aspiration of particulate residues from surfaces is an
advance in the
art. When used with jet-assisted suction sampling heads of the invention,
higher
aspiration velocities result in significant improvement in the capacity to
loosen, mobilize
and aspirate solid materials without elutriative losses.
Particles are the primary information-rich content of any sample, and include
not only
explosives crystals and residues, but also fibers, dust and skin cells
saturated with
adsorbed vapors from contact with explosives and explosives associated
materials
(XAM), including taggants. A rigorous, jet-assisted sampling apparatus, with
capacity
for accumulating particles in a particle trap from a larger volume of
aspirated air, will
improve surveillance and reduce false negatives. A single particle of diameter
of 10
microns may have a mass of about 1 picogram; a particle of diameter 25 microns
a mass
of about 13 picograms; a particle of diameter 50 microns a mass of about 105
picograms:
thus a single particle may be sufficient for detection of an explosive having
200 - 400
MW, even an explosive having negligible vapor pressure.
CA 02742633 2011-06-08
The relevance of particles in detecting explosives is thus readily apparent.
For example,
in a fingerprint containing 100 ng of crystalline explosive (as shown in FIG.
26), solid
particles of size greater than 10 microns will contain 85% of the mass (i.e.,
information
content) of the sample. This data is representative of crystals of RDX, HMX or
PETN.
However, for that same fingerprint where the explosive residue is RDX, the
vapors
present in a liter of equilibrated air above the fingerprint are expected to
have a mass of
less than 8 femtograms of explosive. In other words, the solid residues have
approximately seven orders of magnitude more mass than the equilibrated
vapors,
dramatically shifting the probability of detection in favor of the
investigator who can
detect the presence of particles. Thus the sampling of particles must be a
part of any
comprehensive surveillance strategy for detecting explosives.
One comprehensive solution uses an air-to-air particle concentrator for
focusing and
concentrating particles from a high volume throughput suction intake,
accumulating
particles (and any adsorbed vapors) from a particle-enriched flow in a
particle trap,
accumulating any free vapors in a vapor trap in a bulk flow, and analyzing the
contents of
the particle trap and the vapor trap, either independently or after pooling
any analytes
stripped from both traps. A real time dual detection platform for both vapor
and
particulate explosives residues at high throughput is achieved by combining
jet-assisted
aspiration with skimmer-assisted separation of particles and vapors prior to
capture and
analysis, and advantageously overcomes technical problems that occur where
separation
of a particle-enriched flow and a particle-depleted bulk flow is not
provided..
FIG. 27A is a pictogram of a vapor trap with sorbent resin bed. The sorbent
bed may be
contained in a housing downstream from the skimmer in line with the bulk flow
exhaust.
The sorbent bed is about 1.5 mm in thickness. A twenty-five cent coin is shown
for size
comparison. FIG. 27C is an exploded view of the cartridge of FIG. 27B, which
is
formed of a stack of component layers and inserts into a housing with in-line
connections
to the bulk flow outlet. The overall structure is integrated around a single
ohmic heating
element 1105 for desorbing vapors by heating the resin under a stream of hot
moving
carrier gas, the carrier gas generally flowing in a direction opposite to the
suction flow
used to collect the sample. Fasteners that hold the layers together are not
shown.
46
CA 02742633 2011-06-08
Top and bottom aluminum mounting plates (1107, 1108) are fastened together so
that the
cartridge can be inserted and removed from the housing as a single unit. The
air column
being sampled flows from the bottom of the assembly through a central passage
and out
the top.
From bottom to top, the moving gas sample encounters pervious supporting
layers (1104,
1103) which sandwich a ceramic layer with central cutout, the ceramic layer
1102. The
central well is for receiving a bed of vapor adsorbent beads and the two
surrounding
layers hold the beads in place during operation. The depth of the bead bed can
be seen to
be relatively shallow so that pressure drop across the vapor trap is low.
Resting on the
uppermost support layer is a stainless steel plate 1106 with central open grid
for
supporting the resistive heating coil 1105. A ceramic cuff 1109 that fits over
the coil is
notched 1110 for the passage of electrical wires to the heating coil.
The heating coil is actuated during desorption only, generally during the
analytic step
(IV) and purge step (V) of FIG. 23. Any resulting vapors during initial
desorption are
presented to a detector as shown in FIG. 24B (rightmost, A) or may be
subjected to
further concentration in a secondary focusing trap. The detector may be an in-
line
detector or may be mounted to a tee on the vapor trap housing.
As shown in FIG. 27B, the vapor trap 1100 is a thin layer of adsorbent bed
material
supported in the path of the bulk flow. Adsorbent materials are typically
formed as resin
beads or as coated filaments and may be sandwiched as beds between supporting
pervious structural layers such as of a stiff mesh, using a sleeve or spacer
for controlling
the thickness of the bed. Literature on selection and use of sorbent materials
for SPME
and related preconcentration arts is widely available. Carbon fibers or
coatings may also
be used. The vapor trap is positioned downstream in the bulk flow channel.
An ideal vapor preconcentrator has only one theoretical plate, and an
adsorbate species is
thus adsorbed or desorbed in essentially one fully reversible "on/off'
process. However,
in practical application, efficient vapor trapping necessarily relies on more
complex free
paths and binding site affinities to ensure capture of a variety of analytes.
In our
experience, useful vapor adsorption efficiency, acceptable breakthrough volume
VB, and
shorter desorption time to cleardown, can be achieved at a low pressure drop
and high
47
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throughput rate for light (C2-C5) and mid-range (C5-C12) volatiles typical of
explosives-
associated compounds by reducing bed thickness to that having a pressure drop
of 5
inches of water or less at 1000 L/min through a reasonable surface area. These
conditions describe a thin plate, disk or layer suspended across the gas
stream and having
a thickness of at most 2 mm.
In FIG. 28, capture of DMDNB vapors by a sorbent bed of a vapor trap is
illustrated.
Breakthrough of volatile analyte is detected within 2 minutes at about 1000
L/min in a
thin bed of Carboxen 569 resin after a 2 sec pulse loading. However, up to 70%
of the
initial sample mass is retained on a bed that is less than about 1.5 mm thick
for two
minutes or more. While not shown, particulate material entering the vapor trap
dramatically increases difficulty in obtaining a vapor analyte signal. Vapor
bleed of
matrix interferents, and also explosives and can persist for days after
particle
contamination, limiting the use of the vapor trap for subsequent samples.
Thus the interest in exchangeable cartridges. Exchangeable cartridges
containing a vapor
trap or a vapor/particle trap combination may be used. Disposable cartridges
permit
suspicious samples to be archived or transferred for more extensive analysis,
and also
eliminate the need for expensive maintenance if the vapor trap becomes
contaminated
with a "sticky substance". Off line analysis of vapor sorbent filters is
described for
example in WIPO Doc. No. 2010/095123 and in US Pat. Appl. Doc. 2009/008421).
Sorbent bed life is also increased by avoiding exposure of the sorbent bed to
higher
molecular weight adsorbates, those considered "semi-volatile", by supplying
particle-
depleted air to the vapor trap, high boiling point "sticky" volatiles in the
bulk flow are
largely avoided. Thus the cut size of the particle concentrator is generally
configured so
that particulates are directed away from the vapor trap and to the particle
trap,
advantageously reducing vapor trap fouling.
FIGS. 29A and 29B are plan and cross-sectional views of a sampler head 1250
with
paired jet nozzles 1251 and jet flows 1251' with solenoids 1252, with particle
concentrator having a central intake duct 1254 and sampling bell 1255, and
with a
particle trap 1256 mounted in the housing. Optionally the sampler head can be
mounted
on a wand as shown in earlier figures. An attached vapor trap 1268, such as
described in
48
CA 02742633 2011-06-08
FIG. 27, is depicted schematically, having an in-line connection with the bulk
flow
exhaust port 1269.
Jet operation is as earlier described: jet pulses 1251' are emitted
intermittently by the
action of high speed solenoid valves 1252 at near sonic velocity and have
kinetic effects
at up to a foot away, collisionally dislodging, mobilizing and eroding
materials from
substrates. Multiple jet nozzles ring a central suction intake or are used in
pairs. The jet
pulses may form an intermittent, instantaneous virtual sampling cone in which
particles
and vapors are mobilized and directed as a suction intake flow 1253 into the
suction
intake and central intake duct 1254.
Within the central intake duct 1254, particles are concentrated as a central
particle beam
or ribbon of flowing gas by the focusing action of one or more aerodynamic
lens
elements 1257. The gas stream 1253 is accelerated as the duct narrows and
encounters a
virtual impactor 1258 with skimmer body 1259, skimmer nose 1260, and collector
duct
1261. The bulk flow 1262 streamlines are deflected on the skimmer nose 1260
into
lateral flow channels 1263 while the particle-enriched flow 1264 with
particles flows into
the mouth of the nose, also termed the mouth or void of the virtual impactor
1258. As
shown here, the particle-enriched stream is then stripped of particles by a
mesh-type
impactor 1256 mounted within the nose before exhausting through collector duct
1265.
Downstream pumps for pulling the bulk flow 1262 and the particle- exhausted
flow 1264
are separately controllable and are used to establish a flow split between the
two flows
and also the overall suction intake volume per unit time.
Flow 1262 of particle-depleted gas is directed through a low pressure drop
vapor trap
1268 containing an adsorbent material with affinity for the desired vapor
analyte(s).
Vapor-depleted air 1262' exits the vapor trap housing (drawn to suction blower
1005). In
this way both vapor and particulate fractions of interest may be captured at a
higher
overall sampling flow rate and velocity then would be possible if the flows
were not
separated according to the flow split.
The particle trap 1256 shown here is built as a cartridge assembly 1266
constructed to be
withdrawn from the apparatus. The cartridge comprises a cylindrical sleeve
around the
collector duct and the particle trap member 1256 and inserts into a receiving
port 1267 at
49
CA 02742633 2011-06-08
the base of the collector duct. The receiving port is co-axial with the long
axis of flow of
the particle beam. The cartridge is removable for remote analysis or
archiving.
FIG. 30 is an exploded view of the removable cartridge subassembly 1266. The
nose
end 1270' of the skimmer body 1270 is formed with a central collector duct
1271 and
virtual impactor void 1272 for receiving a particle beam. The nose end is
shown here
with conical forward face for diverting the bulk flow around the nose. The
skimmer body
is mounted in an surrounding housing (not shown) which channels the bulk flow
through
exhaust port 1269 in coverplate 1273. The coverplate, forming the back side of
the
particle trap, is removable. Only a half a coverplate is shown for purposes of
illustration.
The particle beam with associated air flow is directed axially through a
particle trap
member 1256, which includes as shown here three layers of non-conductive mesh
and a
capping thimble nut 1266a and tubular sleeve 1266b. Flow is exhausted at
rightmost
central port 1274. Rearmost nut 1275, threads not shown, secures the tubular
sleeve to
the coverplate, and is threaded for removal. The internal sleeve, cap and
particle trap
(assembled as a "cartridge body" 1266) of this figure are removable for remote
analysis
or archiving. The concentrated volatiles or eluate from the particle trap
cartridge are
presented to an analytic module for detection of explosives residues.
Pervious filter or mesh members 1256 generally are heat resistant and are
selected from
glass or ceramic where electrical interference is to be avoided, such as for
certain in-situ
detectors. However, conductive stainless steel or carbon materials may also be
used if
desired. Encased carbon fiber materials may also be used as a coarser
supporting matrix
to improve heat transfer. In special circumstances, such as disposable
cartridges, plastic
filters or meshes may be used, and analytes may be stripped with vapor or
solvent rather
than heat.
FIG. 31 demonstrates particle mobilization and aerosolization with a jet-
assisted suction
head of the invention. Experimental data are plotted for jet aerosolization of
solid
explosives residues from a surface. The data was collected using the widemouth
sampling bell of FIG. 37 and illustrates the effect of the distance ratio L/d
on
resuspension efficiency, where an explosives residue is applied to a surface
and the
CA 02742633 2011-06-08
residues are then mobilized and eroded by the action of the jet pulse and
aspirated under
suction.
Under choked flow conditions with fast valve actuation, jet pulse energy may
be varied
by selecting nozzle size (or critical dimension). Nozzles may be circular or
may have
asymmetrical shapes, such as fan or chisel shapes. Data shown is for a series
of circular
nozzles. The distance ratio is defined as L/d, where L is the distance between
the jet
nozzle orifice and the substrate and d is the critical dimension of the jet
nozzle. The ratio
is found to have a correlation with particle removal efficiency and can be
seen to scale
linearly. At length/diameter ratios of 30x, recovery is still sufficient to
detect all three
explosives. At lOx jet length to diameter ratios, recovery (1271, solid line)
approaches
unity for more crystalline materials such as TNT, but is less for C-4 (1273),
which is a
plastic explosive and is more clay-like, containing aliphatic oils which are
sticky. RDX,
the active crystalline component of C-4, is shown to be more readily
aerosolized (1272).
Studies by others have shown that fingerprints of persons handling RDX and C-
4, for
example, typically contain crystals larger than 10 microns, and these crystals
contain
most of the total mass, underlining the value of collecting particulate
solids.
Effects of number of layers of filter or mesh on particle capture efficiency
are shown in
FIG. 32. Mesh illustrated here may be one, two, three, five or seven layers
thick for
example; exhibiting increasing efficiency of capture. Capture efficiencies
approaching
100% can be obtained; coarse mesh in fewer layers has lower efficiency than
finer mesh
in multiple layers. Experiments were performed with dried crystalline residues
of TNT
1274 applied to a surface and sampled. Similar experiments were performed with
RDX
crystals 1275 and with C-4 1276, a more sticky substance which contains
plasticizers.
Because the bulk of the air volume aspirated has been diverted in the skimmer,
lower
pressure drops, smaller particle traps, and higher particle capture
efficiencies are
achieved.
Particle capture efficiency is negatively impacted by particle scattering and
elutriative
losses. FIG. 33 demonstrates the effect of settling in flight on capture
efficiency. When
operating at distances of a few inches or more than ten to twelve inches from
a suspicious
residue, particles dislodged by a jet pulse can be drawn into a suction intake
but will also
51
CA 02742633 2011-06-08
tend to resettle. Elutriative effects are readily apparent for larger
particles and higher
density particles. The solid line 1277 indicates capture efficiency in a
particle trap with a
cut size of about 5 microns when the head is held vertically downward; the
dotted line
1278 when the head is horizontal to the ground plane. Whereas capture
efficiencies are
quantitative for the vertical orientation in the range of 10 to 40 microns, a
small loss of
sampling efficiency is noted in the horizontal head position with larger
material. These
data are taken at a suction intake rate of 800 sLpm in a conical head with a
5.5" mouth.
More significant losses are noted at slower suction intake rates. Higher
collection
efficiencies are achieved at higher velocities in the intake bell or nose.
For portable surveillance systems, it would be common for a sampler head to be
held at a
somewhat horizontal orientation. The data indicate the need for higher linear
flow
velocities in the intake nose to minimize settling dropout. In heads with bell
size
maximal diameter of greater than about 5 inches, for example, a linear in-flow
velocity is
at least 0.8 m/ is deemed sufficient to efficiently aspirate the majority of
particles of 5 to
100 microns aerodynamic diameter without major settling losses. Higher linear
intake
velocity with acceptable pressure drops across a smaller cross-sectioned
particle trap is
realized, happily, by inserting an air-to-air particle concentrator between
the suction
intake and the particle trap. Further increase in volume throughput may be
achieved by
reducing the pressure drop for the bulk flow and by increasing the flow split.
Efficiency data are useful in optimizing jet and suction configurations for
efficient
particle resuspension and aspiration. FIG. 34 plots optimization of jet
diameter by
measuring overall sampling efficiency il, (1279, solid line) for explosives
residues from a
solid surface at a constant distance. Removal efficiency approaches 100% for
crystalline
solids such as TNT, but is less for softer explosives such as C4, apparently
due to surface
associations of the solid particles. RDX is intermediate. Even at distance
ratios of 30x
or 40x nozzle diameter, however, removal efficiency is a substantial
percentage and
particulate and particulate-associated explosive residues are readily
detectable.
As jet diameter increases under choked flow conditions, particle removal
efficiency 11R is
seen to increase, indicating greater kinetic energy of the jet pulse; however,
aspiration
efficiency 11A, indicating particle capture, decreases almost inversely,
indicating that
52
CA 02742633 2011-06-08
particles are scattered outside the sampling zone. In this example there is an
optimum
balance, as seen by a peak in overall sampling efficiency 11s is apparent at a
jet diameter
of about 3 mm. This result has been repeated under a number of experimental
conditions
and represents a useful approach for optimization of sampler head
configuration.
The force of the jets in eroding materials from a surface is illustrated in
FIGS. 35A and
35B. Aerosolization of standing water on a surface with a three millimeter jet
array at a
standoff of 6 inches is shown. Open diamonds indicate background particle
content of
aspirated air as measured with a laser scattering particle counter. Solid
squares indicate
aerosolized material from the same surface with standing water after impact of
a single
jet pulse. The increment in particles detected, FIG. 35A, indicates an
increased
concentration of 10 and 15 micron particles (i.e., mist) in the aerosol
sampled from the
wet surface. Similarly, in FIG. 35B, overall aspirated mass is greater from
the wet
surface, indicating that standing water is aerosolized by the impact of the
jets and
microscopic water droplets in the 5 - 15 micron range are aerosolized in this
way and
may be sampled in the suction in-flow of the sampling device. The force of the
jets is
graphically illustrated and demonstrates the beneficial erosive effects of
high velocity gas
jets in obtaining samples from contaminated surfaces.
Interchangeable detector heads are provided, as is useful to increase
flexibility in use.
FIG. 36 shows a sampler head 1280 having three interchangeable nose
attachments
(1281, 1282, 1283). Each tool is adapted to a particular kind of sampling, a
first nose
attachment 1281 with four jets 1251 and a wide intake bell for surface
sampling
(generally for fixed or robotic emplacement), a second attachment 1282 with
smaller
intake bell and two jets 1251 for portable use in surveilling surfaces, and an
extended
narrow nose 1283 with paired jets 1251 for interrogating narrow or hard to
reach spaces.
The "general purpose" interchangeable head depicted centermost is also useful
for
surveillance of persons and can be directed at clothing, hands, shoes and so
forth.
The narrow elongate nose 1283 depicted rightmost in FIG. 36, is useful for
probing
narrow cracks, corners, and also for insertion into holes such as through a
layer of shrink
wrap surrounding goods on a pallet, where the enclosing wrapping layers ensure
that
53
CA 02742633 2011-06-08
particles and vapors that are mobilized by the jet pulse are not scattered
away from the
suction intake but are instead deflected into the suction intake.
Nose attachments with four jets and two jets are shown, but the number of jet
nozzles
(1251) may be varied as indicated in FIG. 3B - 3D or reduced to two jets or
even one jet
where it is desirable to insert the sampling nose into a tight space.
The sampler head body 1280 generally also includes any control mechanisms for
pulsatile emission of jets (here a pair of solenoids 1285 are shown), any
pressure
reservoir and manifold useful for supplying and distributing pressurized gas
feed to the
jets, an air-to-air particle concentrator, a collector duct, pumps and any
power supplies as
required. Thus any wiring connections need not extend into the sampling nose
attachments. The nose attachments include jet nozzles 1251 for directing jet
pulses onto
a substrate and a central suction intake for aspirating a gas volume and any
associated
vapors and particles. Tubulations are not shown for simplicity. The body is
provided
with a generic interconnect mechanism (here three nipples 1286a,b,c) so that
each of the
nose tools are engaged with a sealed and air-tight connection. Other sealable
connectors
are known in the art.
For enclosed spaces, two jets are typically sufficient although it may be
desirable to
control or vary jet incidence angle to better sample the walls of any crevice
or cranny that
is being interrogated. For larger surfaces and for situations where a sampler
head
traverses a surface (or a surface is moved beneath a sampler head) four, six
or eight jets
may provide additional efficiency in particle removal.
Because the jet pulses have a kinetic energy, any flexible walls or wrappings
of parcels,
letters, luggage and boxes are readily collapsed by the propulsive force of
the jet and then
reflated under vacuum, causing fractions of air to be expelled from inside the
package or
bag. Serial pulse trains are particularly useful in exploiting this percussive
effect. The
jet-suction head thus is superior to plain suction in mobilizing residues from
inside
parcels. In this way, false negatives are more readily avoided.
FIG. 37 is a first sampling nose 1281 configured as a widemouth surface
sampler with
quad jets 1251a,b,c mounted on a sampling bell 1287. In this view, the
sampling end of
the bell is pointed away so that an interconnect manifold 1289 is visible. Gas
entering
54
CA 02742633 2011-06-08
the sampler head at ports 1288a,c is distributed to each of the four jet
nozzles mounted on
tubulations around the bell. When attached, central intake 1290 with socket
1288b is in
fluid communication with the air-to-air particle concentrator and the suction
blower.
In one embodiment, the widemouth bell has an internal diameter of about 5.5
inches at
the inlet end and a conical profile, terminating in central intake duct 1290
with an internal
open diameter of about 1.77 inches. The suction velocity at the wide end (of
the sampler
cone is about 1 m/s at 1000 L/min. The suction velocity at the narrow end
(1.77 inch
diameter) of the cone, at the point of entry into the particle concentrator,
is about 10 m/s
under these conditions.
Aaberg lateral flows may be employed to extend the forward reach of the
suction low
pressure zone and more parallelly align in-flow streamlines. Since a large-
volume
regenerative air flow is readily available for feeding lateral flows (the bulk
flow exhaust
from the sampler head), the Aaberg effect can be readily achieved at little to
no energetic
cost for device operation.
FIG. 38A illustrates a sampling nose 1291 modified for sampling from crevices
and
enclosed volumes, where the jet orifices are provided with directional jet
nozzles
1292a,b. Jet nozzles with other angulations and shapes may be used. For
interrogation of
tight and enclosed spaces, which may be spaces between or inside boxes, under
pallets,
along the baseboards of walls, and inside trunks of cars, for example, the jet
will impinge
on the surrounding surfaces with a variable angle. Because of the enclosing
geometry of
the sampling space, the dispersive angle of the jets is not an impediment to
aspirating
materials that are dislodged.
As suggested by FIG. 38B, the jets can be configured with a compoundly bent
directional
nozzle 1293 to propel the sampling nose in a spinning, circular motion so as
to dislodge
residues from the surfaces enclosing a space.
FIGS. 39A and 39B are perspective and exploded views of a spinning jet nozzle.
The
directional nozzle 1295 itself may spin, for example a jet nozzle having
journalled
surfaces and bearing means for rotating, where a complexedly bent jet nozzle
1294 is
mounted with needle bearings 1295 on a journalled nipple 1296 and fluidly
supplied with
pressurized air so that it spins in reaction to the jet pulse exhaust. When
sampling in
CA 02742633 2011-06-08
enclosed spaces, an actively spinning jet with variable incident angle is an
assist in
dislodging and mobilizing materials from various surface orientations
encountered as
probe advances. The angle of the jet may be orthogonal to, oblique to, or,
more
preferably, acutely angled relative to the directional axis of the sampling
nose at any
given time. Alternatively, the head may be fitted with flexible hose tips as
varidirectional
jet nozzles for sampling enclosed spaces. The flexible hose tips have an
elasticity that
promotes a whip action that promotes mobilization and erosion of any
particulate or
vapor analytes on the walls or floor of the enclosed space.
FIG. 40 is a face view of a two-piece sampler head 1300 with internal
pneumatics
shown. The forward face 1302 of the jet-suction nose, which may be directed
into a
narrow crack, corner or orifice, contains a central suction intake 1303 and a
pair of
peripherally disposed jet nozzle outlets 1304a,b. Emitted jet pulses are
directed with a
forward velocity and strike any exposed surfaces within proximity, dislodging
adherent
materials and stripping away any vapors in the boundary layers. The entrained
materials
are pulled into the suction intake by a suction blower operatively connected
to the
sampler head. The suction intake flow is formed into a particle-enriched flow
and a bulk
flow by the action of aerodynamic lenses (1305a,b,c) and the progressively
narrowing
intake channel, which functions as an accelerator. A slit-type skimmer 1306 is
used to
separate the particle ribbon flow from the bulk flow. Particles are directed
into a
collector duct 1307 and accumulate in a trap downstream from the skimmer for
periodic
analysis.
Functionality of skimmers having concavoconvexedly reverse curved lateral
channels
1308 for the bulk flow is described in more detail in US Pat. No. 7,875,095
and co-
pending US Pat. Appl. No. 12/964700, which are co-assigned and are
incorporated in full
by reference. Briefly, the downstream walls of the lateral channels are shown
to support
the bending streamlines of the bulk flow in turning more than 90 degrees from
the long
axis of flow of the gas streamlines in the suction intake, the downstream wall
support
serving to reduce eddies and wall separation instabilities so as to promote a
cleaner
separation of the bulk flow from the particle-enriched flow. The bulk flow and
particle-
enriched flow streams diverge above the virtual impactor mouth, shown here
with a
56
CA 02742633 2011-06-08
generally "cross-tee" configuration 1306' with four channel arms in section.
This
geometry is useful for both slit-type and annular (axisymmetrical) skimmers.
FIGS. 41A and 41B are cross-sectional views of a particle concentrator
assembly 1313
with integrated particle trap 1314 (here shown as a single pervious sieve
element) and air-
to-air particle concentrator with aerodynamic lenses (1305a,b) and skimmer
"tee"
(1306'). Close proximity of the trap to the virtual impactor mouth 1315 is
found to
reduce deposition losses in the collector duct 1316. Serendipitously, forming
the lateral
arms 1317 of the skimmer with a concavoconvex reverse turn (i.e., greater than
180
degrees) away from the long axis of flow through the skimmer nose 1318 as
shown
provides more lateral space in the skimmer body 1320 for a particle trap
mounted in a
stopcock-like rotatable cylinder body 1321 directly below the virtual impactor
mouth. In
these views, the particle trap is rotatable on an axis and may be turned from
a position
coaxial with the long axis of flow to a secondary position for extraction of
analytes and
downstream analysis. The suction intake gas stream 1322 is split above the
virtual
impactor mouth 1315 into two arms of a bulk flow 1323a/b (which is diverted
into the
lateral flow channels 1324) and a particle ribbon flow 1325' (which is
directed down the
central collector duct 1316 and through particle trap 1314, where it is
stripped of particles
before being exhausted at 1316').
Also occupying the skimmer body 1320 is an injection circuit or loop with
inlet 1330 and
outlet 1331. The injection circuit is a pneumatic (or hydraulic) injection
channel or loop
and interfaces with rotatable cylinder 1321 that houses the particle trap. In
FIG. 41A, the
cylinder is in a first position so that center passageway (termed the "trap
hollow volume"
1327) is fluidly confluent with the long axis of the central collector duct
1316; in FIG.
41B, the cylinder has been rotated 90 degrees to a second position and the
trap hollow
volume is oriented crosswise. In the second position, the trap hollow volume
is confluent
with injection ducts (1330, 1331) and the movement of an injectate through the
trap
hollow volume is shown as a black arrow. The injection duct is provided with a
pump or
suction for conveying the injectate to a detector in a small volume and is
heated if
necessary. Alternatively the injection circuit may convey any analyte
recovered from the
particle trap to a secondary focusing trap for further concentration.
57
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The two views thus correspond to two steps of a sampling and analysis cycle.
In a first,
"normal" position, the trap hollow volume 1327 and particle trap 1314 are
aligned with
the long axis of the suction intake 1322 and are positioned to capture any
particle
concentrate in the intake flow for a defined period of time, for example one
minute. In a
second "orthogonal" position, the trap hollow volume is aligned crosswise as
is
convenient for stripping volatiles (or solutes) from the particle trap into
the injection duct
circuit within the skimmer body.
Advantageously, no separate valving is needed and, in both positions, flow is
through the
particle trap mesh, not crosswise over it. The particle "cut size" of the mesh
or filter is
generally about 5 microns. Reliable collection of particulates in the range of
5 to 100
microns is associated with a higher degree of detection sensitivity at a
reasonable energy
cost. The system has been shown to be operable at suction intake flow rates of
500 to
1500 sLpm , while not limited thereto, but the flow of particle concentrate
through the
particle trap is substantially less (as dictated by the flow split) and may be
5 to 15 sLpm
or less, for illustration. The overall preconcentration factor on a volume
basis can thus be
about 750,000x or more. The preconcentration factor is equal to the total
aspirated
volume 1322 (which can be up to 1500 liters or more per minute) divided by the
hollow
trap volume 1327 of injectate plus any volume in the injection loop. For slit-
type traps
trap deadspace will be perhaps 1 - 3 cc3, but for annular traps, sub-
milliliter traps are
possible (see US Pat. Doc. No. 2010/0186524, which is coassigned). The small
volume
achieves significant improvement in preconcentration over systems lacking an
air-to-air
particle concentrator. Since only a single particle of sufficient mass is
required for
detection, the lower limit of detection is the limit of the analytical
detector itself per
person, container, pallet, vehicle, and so on. Thus a limit of detection by
mass
spectrometry is conservatively 100 picograms or less per sample [Committee on
Assessment of Security Technologies for Transportation, 2004, Mass
Spectrometry for
Trace Detection of Threat Agents, In, Opportunities to Improve Airport
Passenger
Screening with Mass Spectrometry. The National Academies Press, Washington,
D.C, pp
15-28.] Importantly, reduction of interferents by selective stripping (either
selectively
stripping analytes of interest or selectively stripping interferents, such as
by solvent
58
CA 02742633 2011-06-08
elution or thermal ramping) may improve sensitivity by eliminating or reducing
background signals.
In FIG. 41B, the particle mesh is shown to be mounted in a cylindrical
stopcock or body
1321 and by turning the cylindrical body, the mesh is now aligned parallel to
the long
axis of flow in the collector duct, but in line with secondary injection
ductwork for
collecting volatiles (or an eluate). By heating the skimmer body and
associated ducts
(shown are heating elements 1333a/b), any particulate materials can be warmed
in a very
small volume of carrier gas to a temperature where they evaporate. Hot carrier
gas (or
liquid) can also be used to heat the particles convectively, as in a
circulating closed loop.
The warm gas mixture (or liquid) can then be conveyed, by positive pressure or
by
aspiration, directly or indirectly into a detection apparatus such as a mass
spectrometer,
or into a focusing trap.
Following desorption, the mesh can be returned to the first "normal" position
and heated
more aggressively to incinerate or char remaining particulate materials. The
ash and
residues can then be blown from the system, either with suction or more
preferably by
reversing the pump so as to blow the material out the front end of the
apparatus.
Other particle trap configurations may also be used, such as an electrostatic
trap, a liquid
impinger, a bluff body, or an inertial impactor plate mounted in a
repositionable body that
intersects the collector duct. Optionally, the cylindrical body is a
disposable cartridge
and can be removed from the particle concentrator assembly for off-line
analysis or
archiving.
In one explosives detection system, the particle concentrator assembly 1335
may include
a centrifugal impactor 1336 as shown in FIG. 42, skimmer assembly 1337, and
aerodynamic lens elements (1338a,b,c). Various centrifugal impactors have been
described in more detail in co-pending and co-assigned US Pat. Ser. Nos.
12/833665 and
12/364672, which are incorporated herein in full by reference. Advantageously,
aligning
the lateral arms of the skimmer "tee" (1339) in a reverse concavoconvex
curvature
increases the space below the virtual impactor for positioning the sinusoidal
bends 1340
of the centrifugal particle trap proximate to the virtual impactor mouth.
Particles are first
concentrated as a particle beam in the focusing section of the particle
concentrator
59
CA 02742633 2011-06-08
(shown here as a series of three aerodynamic lens elements in an intake
channel). The
particle beam is then separated from the bulk flow where the channel
bifurcates in the
skimmer assembly 1337, (shown here with a virtual impactor mouth opening to a
collector duct 1342 for receiving the particle beam or ribbon and with lateral
channels
1343 for receiving the bulk flows 1344). Bulk flows exit the skimmer in
channels
disposed contralaterally around the central "tee" in section, the head of the
tee forming
the mouth of the virtual impactor. Bulk flow is driven by a suction blower
disposed
downsteam from the skimmer. The particle beam or ribbon enters the virtual
impactor
mouth and continues along collector duct 1342, shown here with conical intake
section.
The particle concentrate stream is then subjected to bending of gas
streamlines so that
particles inertially impact the walls of the particle trap (shown here as a
double "U"
1340) in a curved section or loop of the trap, where they are captured. The
dimensions
and operational configuration of the particle trap determine the size of the
particles that
will be captured according to a Stoke's number. The particle trap exhaust 1345
is fluidly
connected to a downstream suction pressure source. The particle-enriched flow
1346 is
exhausted of larger particles in this way and may be discarded.
With suitable detectors, particulate material can be analyzed directly in the
trap by
spectrometric means. Or constituents that are stripped from the particle trap
are
conveyed to an analytic module for analysis. In a preferred system, the
particle traps of
FIGS. 41 and 42 can instead be sampled by injecting a small volume of solvent
for liquid
extraction rather than carrier gas for evaporative transfer. A liquid sample
results.
Liquid elution of particular analytes or classes of analytes may be
accomplished using
one or more chemically selective solvents. Selective elution can be
advantageous in that
insoluble interferences are left in the trap for subsequent incineration or
purging, thus
achieving not only preconcentration but also pre-purification. Ultrasound may
be used to
enhance elution and may also be used to clean fouled surfaces of the particle
trap. Such
liquid samples are compatible with liquid chromatography, including reverse
phase and
ion chromatography, and with electrospray mass spectroscopy, for example. The
repertoire of liquid-based detection methods available are vast and are not
reviewed here.
Alternatively, a liquid sample may be vaporized for gas phase analysis or may
be
subjected to solid phase extraction in a focusing trap prior to analysis.
Advantageously,
CA 02742633 2011-06-08
solvents may be selected exclude insoluble materials such as minerals, ash,
and hair but
readily and selectively solubilize constituents of interest associated with
the skin
particles, hairs, dust, explosives crystals, and so forth. In our hands,
acetonitrile has
proved a useful solvent for elution of explosives, successfully eluting both
RDX and
TATP, for example. Dimethylformamide, tetrahydrofuran, butyrolactone,
dimethylsulfoxide, n-methyl-pyrrolidinone, propylene carbonate, acetone,
ethylacetate,
methanol, water, and chloroform are also useful and may also be used to
selectively
remove interferences in some instances. Also useful are solvent mixtures and
gradients
thereof, as have been described by DL Williams and others.
A coating of carbon in the particle trap may be used to enhance capture of
volatiles and
vapors associated with the particle-enriched stream. While carbon has a very
high
affinity for many vapors, hot solvents are generally more effective in
releasing adsorbed
vapors than heat alone.
FIGS. 43A and 43B illustrate a centrifugal particle trap integrated into a
stopcock-like
rotatable cylindrical body in the collector duct immediately downstream and
proximate to
a skimmer "tee" 1339 and ADL outlet 1347. At the high throughput of suction
gas flow
needed for effective surveillance, miniaturization of this sort is not
possible with earlier
technologies. Without a suitable flow split, as obtained by upstream air-to-
air
preconcentration of the particle beam or ribbon, an acceptably low pressure
drop and
velocity of the airstream transiting the particle trap would be impossible to
achieve,
resulting in particle losses. As shown in FIG. 43A, the cylindrical body 1348
is in a first
position (I) fluidly confluent with the collector duct 1349 and in FIG. 43B in
a second
position (II, rotated 180 degrees) fluidly confluent with small bore inlet
1350 and outlet
1351 injector ducts that form an alternate pathway or loop for an elution
solvent or for a
hot carrier gas. The skimmer body and stopcock are optionally heatable on
command.
In FIG. 43A, a suction flow is established, bulk flow is diverted at skimmer
tee 1339, and
air bearing the informationally rich particle concentrate is introduced into
the particle trap
(first position, I). Particle-exhausted air 1352 exits the particle trap at
1353 and is
discarded (or may be routed to a vapor trap if desired). Particles are trapped
inertially in
the curved "U" of the particle trap, the internal volume of which constitutes
a "trap
61
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hollow volume". Bulk flows 1354 are drawn through lateral arms 1355 by a
downstream
suction blower.
In FIG. 43B, the "stopcock" has been rotated 180 degrees so that the fluid
path is now
confluent with the sampling ducts. Suction flows are stopped for the duration
of an
analytical cycle, where constituents of any particle concentrate in the trap
are analyzed.
In this second position (II), elution solvent or hot carrier gas is injected
through the
particle trap and conveyed to an analytic instrument, to a focusing trap, or
to a device for
archiving or secondary processing. A highly concentrated liquid volume (or
carrier gas
volume) is generated 1356. Since the trap hollow volume 1357 of the rotating
member
1348 is generally less than a milliliter, the overall preconcentration factor
PF is minimally
5000x for a two second aspiration at 300 L/min, and 1,000,000x for a 60 sec
aspiration at
1000 L/min (a one million-fold preconcentration by volume). In short,
efficient
aspiration of a single particle can result in a positive detection event.
In a fully integrated system, the system combines a jet-suction nose for
drawing a suction
flow, an air-to-air particle concentrator for separating a bulk flow from a
particle-
enriched flow, a particle trap with integrated mechanism in the skimmer nose
for
collecting explosives-associated residues, and valveless means for conveying
captive
volatiles or vapors from the particle trap to a detection means. Yet more
compact
systems with detection means for screening particulate residues incorporated
in situ in the
particle trap, such as described in WIPO Pat. Doc 2004/027386 or for in situ
spectroscopy, are also conceived.
FIG. 44 depicts a second valveless system 1360 for eluting or thermally
desorbing
explosives-associated residues from a pair of particle traps (1361, 1362)
disposed in a
trap hollow volume within a reciprocating member 1363. For illustration,
particle trap
members in this device are sieve or mesh-type members that are generally
rectangular in
shape for receiving a particle-enriched gas ribbon from a slot-type virtual
impactor via
collector duct. Suction intake gas 1364 enters a collector duct 1365 at the
top as a
particle-rich flow and exits at the base of the collector duct 1365' as a
particle-exhausted
flow 1366; particles are trapped on one of the pervious filter elements (1361,
1362) in
alternation, depending on the position of the reciprocating body. The
reciprocating body
62
CA 02742633 2011-06-08
has translational freedom to slide transversely between a first position (FIG.
44A) and a
second position (FIG. 44B).
In FIG. 44A, the first particle trap 1361 is situated in line with the
collector duct 1365
and the second particle trap 1362 is situated in fluid communication with an
injector
duct, the injector duct flow (black arrow, 1370) traversing inlet 1371 and
outlet 1372.
While the first particle trap is accumulating particles, the second particle
trap is in
analysis mode. Carrier gas or solvent (I) is injected at inlet 1371 through
the particle trap
and constituents of interest are conveyed from pervious member 1362 to a
downstream
analytic module. Heat may be used to stimulate particle dissolution or
volatilization.
In FIG. 44B, the stations are reversed: while the second particle trap is
accumulating
particles and suction 1364 is flowing, the first particle trap is in analysis
mode. Carrier
gas or solvent flow (black arrow, 1380) is injected (II) through a second
injection duct
with inlet 1381 and outlet 1382. The flow contacts pervious member 1361 and
constituents of interest are conveyed to an analytic module. During this
operation, the
particle-enriched flow is directed through the second particle trap 1362 and
more
particles are accumulated.
The system is thus capable of essentially continuous operation by alternating
collection
and analysis modes between the two particle traps. Conditions during the
dissolution or
volatilization part of the cycle may be intensified so that regeneration of
each trap is
accomplished before the trap is returned to the collection station. As
required, the body
surrounding the trap and the cylindrical sliding body may be heated. When not
in use,
the injector pathways are blocked by the body of the reciprocating member,
thus there are
only two passages through the reciprocating body, each constituting a trap
hollow
volume. This feature eliminates the need for supplementary valving. Not shown
is a
cavity in the sampling head for receiving the reciprocating member. O-rings,
gaskets,
and registration features as would be useful in operation of the device are
well known and
are not shown for simplicity of illustration.
FIG. 45 illustrates a cartridge body 1390 formed with a single passageway or
"trap
hollow volume" 1391 with particle trap 1392 disposed therein. The particle
trap is
depicted as a pervious filter member in a channel through the cartridge body,
the channel
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with inlet 1393 and outlet 1394 for aligning with a collector duct of a
skimmer body. The
cartridge body is adapted to be sealably inserted into a receiving cavity of a
sampling
head and includes a handle 1395 for easy removal. The walls 1396 of the
cartridge body
are adapted with seals 1397a,b and a key pin 1398 so that the cartridge may be
inserted
and locked in place in a cartridge receiving cavity of the sampling head, the
trap hollow
volume aligning itself to be sealed and fluidly confluent with the collector
duct of a
skimmer (as depicted previously) so that a particle-enriched gas stream must
pass through
the pervious filter member during particle concentration and collection.
Cartridge bodies
of this type may be periodically replaced so that the used cartridge with any
accumulated
particles may be handled off-line and inserted into a specialized sample
receiving vessel
of an analytical instrument for detailed analysis of particle constituents.
FIG. 46 (Table 2) lists some explosives likely to be encountered and lists
patterns of their
detection by a combined particle and vapor dual detector system of the
invention. A
broader range of analytes is detected with two independent channels than with
either a
particle or a vapor channel alone. In certain instances, combined detection
provides
unique signatures, such as detection of DNT in the particle trap and
diphenylamine
(DPA) in the vapor trap, an indication of smokeless powder. Detection of 2-
ethylhexanol
in the vapor trap and bis-(2-ethylhexyl) phthalate (DEHP) in the particle
trap; or
cyclohexanone in the vapor trap and nitrocellulose in the particle trap, are
both
indications of PETN-based plastic explosive matrix materials. Thus vapor and
particle
co-detection can overcome false negatives even when an explosive itself is not
detected.
Because vapor analysis frequently involves thermal desorption, EGDN (which
can.
decompose at 115 C) may be more readily detected in a particle trap that uses
liquid
elution or cold detection; and similarly DMDNB is sticky and likely to cling
to
particulate materials it comes in contact with. But many industrial solvents
are very
volatile and are less likely to be retained with a particle fraction under
high throughput
sampling conditions. These chemicals include materials not always associated
with
explosive manufacture but when detected in a vapor trap along with any
simultaneous
detection of a nitrate, perchlorate, or plasticizer in the particle trap, for
example, an alarm
is triggered. The systems thus have learning capability to recognize and
distinguish
innocent and suspicious chemical signatures based on dual channel detection,
where the
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vapor channel is optimized for lighter molecular weight materials and the
particle trap is
optimized for heavier and stickier materials. Taken together, substantial
confidence in
detection across a wider range of known and as yet unknown explosives is
achieved.
FIG. 47 is a schematic view depicting implementation of a sampling apparatus
1400 for
automated inspection of parcels. Parcels 1401 advancing on a conveyor belt
1402 pass
under or through a supporting frame 1403, here shown configured with a single
sampler
head 1404. The sampler head is configured for emitting a train of jet pulses
at high
velocity against the packages from a distance of up to about 30 cm, so that
particle and
vapor residues associated with external and internal surfaces the parcels are
mobilized. A
suction intake is operated simultaneously to aspirate any particles and
associated vapors
eroded from the parcel surfaces by the action of the jets. Power and any
positive and
negative air pressures are supplied via an umbilicus 1405 from remote support
module or
cart 1406. Analysis may be performed within the sampler head or remotely.
Multiple
sampler heads may be used to inspect multiple faces of the baggage stream.
Similarly, a
portal with suction passageway for surveilling persons may also be
constructed.
FIG. 48 is a schematic view depicting deployment of a sampling apparatus with
sampler
head array for inspection of vehicles. Vehicles 1411 advance through an
overhead frame
1412 fitted with multiple sampler heads 1413 of the invention. The sampler
heads 1413
focus a pattern of jet pulses on the exterior surfaces of the vehicle to
aerosolize any
residues deposited thereon and aspirate any aerosols and associated vapors
that are
generated. Power and positive and negative air pressures are supplied via an
umbilicus
1414 from remote utilities and control module 1415. Each sampler head is
generally
configured to trap particles and vapors within the head. Analysis may be
performed
within the sampler head or remotely, optionally with evaporative collection of
volatiles
for conveyance to a central analytic module in heated lines. Preliminary
detection is
preferred, where a detection means is incorporated in the individual detection
head.
Cartridges requiring more detailed analysis may be removed from the sampling
head(s)
and analyzed at a remote workstation. Cyclical regeneration of the trap(s)
between each
vehicle inspected, typically by reversing the air flows, may be necessary to
avoid fouling
of the particle traps. Incineration and ultrasound may also be used to keep
particle traps
CA 02742633 2011-06-08
clear in the presence of large amounts of road dust. Use of ultrasound is
described in one
or more of our co-pending applications.
A number of methods may be used to augment the capacity of the sampler head to
strip
off particles and vapor residues from substrates. One such technique is a jet
gas feed
ionized by contact with a source of ions, such sources including but not
limited to a
"corona wire," a source of ionizing radiation, a glow discharge ionization
source, or a
radio-frequency discharge. The ionized gas stream is used to neutralize
electrostatic
associations of particles with surfaces and improve lift off of particles.
Collisions of higher molecular weight gas atoms or molecules results in
improved
desorption of particulate and vapor residues. The carrier is typically air,
argon or
nitrogen and the gas or solvent is a high molecular weight molecule sufficient
to aid in
dissociation of particles and volatile residues from the object or
environmental surface of
interest. Pressurized gas tanks eliminate the need for an on-board compressor,
thus
reducing power requirements for portable applications. The presence of organic
vapors
also can aid in volatilizing chemical residues such as explosives and will
compete with
organic molecules for binding to solid substrates. Heated jet pulses or
infrared lamps
directed from the sampling head improve sampling efficiency for vapors,
however, it
should be recognized that premature heating can reduce particle collection;
and contrary
to the teachings of others, near sonic jet pulses are preferable to hot air
for aerosolizing
particles from substrates.
Hot solvent vapor also increases the specific heat capacity of a hot carrier
gas stream and
can improve convective heating of sorbent beds, aiding in desorption of
constituents of
interest and in cleardown.
EXAMPLE
In one study, 20 nanograms of TNT trace explosive was deposited on a glass
surface
using a dry transfer technique from a Teflon Bytek strip and interrogated
with a surface
sampler of the invention. The dry transfer technique was performed essentially
as
described by Chamberlain (US Pat. No. 6,470,730). Particle size distribution
(crystal
size distribution) was about 10-200 microns. The apparatus was operated with a
3mm jet
array at 80 psig back pressure. The dislodged TNT particles were aspirated at
a 1000
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sLpm flow rate into a high flow air-to-air particle concentrator with
aerodynamic lenses
and skimmer and captured in a particle trap formed of a 13 mm pervious member.
Explosives constituents of captive particles were dissolved into 100 L of
acetonitrile of
which 10 L was injected into an IMS detector. A measurable TNT signal was
observed.
The experiment demonstrates detection of trace explosive residues at a
nanogram
detection level using a jet-assisted non-contact sampling head of the
invention.
While the above is a complete description of selected embodiments of the
present
invention, it is possible to practice the invention use various alternatives,
modifications,
combinations and equivalents. All of the U.S. patents, U.S. patent application
publications, U.S. patent applications, foreign patents, foreign patent
applications and
non-patent publications referred to in this specification are incorporated
herein by
reference in their entirety. In general, in the following claims, the terms
used should not
be construed to limit the claims to the specific embodiments disclosed in the
specification
and the claims, but should be construed to include all possible embodiments
along with
the full scope of equivalents to which such claims are entitled. Accordingly,
the claims
are not limited by the disclosure.
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