Note: Descriptions are shown in the official language in which they were submitted.
21~9S94
``~- SAMPLER/DESORBER UNIT FOR DETECTION OF
DRUG AND EXPLOSIVE PARTICULATES
Field of the Invention
This invention relates in general to illicit drug and
explosive detection equipment, and more particularly to a
sampler/desorber unit for collecting vapours of
particulates of certain drugs and explosives and
transferring the collected particulates in vapour form to
a remote location for subsequent analysis.
Background of the Invention
In the practice of law enforcement against the
transport of illicit drugs by traffickers, and of explosive
charges by terrorists, a number of devices have been
employed for the detection of these undesirable substances.
Among the most specific and sensitive of these devices have
been analytical instruments, based on gas chromatography,
ion-mobility spectroscopy and mass spectrometry.
Ultimately, all these devices operate on a vapour
phase detection for indication of the presence of specific
substances. Some of these substances have a sufficiently
high intrinsic vapour pressure (e.g. EGDN (in dynamite), NG
and TNT) to provide detectable vapours in their vicinity.
Others, including cocaine, heroin, and the "plastic"
explosives (RDX and PETN) have little or no vapour pressure
at room temperature and, therefore, cannot be detected
through the analysis of ambient air.
These low vapour pressure substances, however,
commonly occur in fine particulate form, either as loose
powder (cocaine or heroin) or with a plasticized binder
("plastic" explosives). Fine particulates of these
substances are prone to adhere to objects with which they
have come in touch, either hands, clothing, suitcases, etc.
It has been well demonstrated that such particulates may be
effectively collected, variously by vacuuming, or swabbing,
etc., and then vaporized by heating so that the resultant
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vapour may be passed into a suitable analytical device, for
detection.
Unfortunately, the process of collection of these
particulates, in most environments, results in the
collection of a sample containing much extraneous material,
both organic and inorganic, which is far greater in mass
than the targeted substances. The presence of this
extraneous material is detrimental to the proper
functioning of the detection system. For one thing, if the
entire sample were vaporized, the resultant vapours would
overload the sensitive detector. In addition, the solid
residue left after heating of the sample would impede the
collection of the next sample.
Summary of the Invention
It is an object of an aspect of this invention to
provide a sampler/desorber unit, for the collection of
particulates of certain drugs and explosives, in dirty
environments, and for the transfer of any such
particulates, in vapour form, to another point where the
target substances will be deposited, relatively free of
extraneous matter. The resultant sample is then more
suitable for subsequent analysis in an appropriate
analyzer.
According to the present invention, an apparatus is
provided for collecting for analysis, particulates of
target substances in an environment which contains
considerable extraneous particulates. The apparatus
includes a first metal screen surface for collecting a
sample including all particulates, a heater for maintaining
the first screen surface at a temperature high enough to
volatilize the target particulates, but not the less
volatile particulates, and a second metal screen surface
for collecting the volatilized vapours from the
particulates.
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Brief Descri~tion of the Drawings
A detailed description of the invention is provided
herein below with reference to the following drawings, in
which:
Figure 1 is an elevation view of a sampler/desorber
unit according to the preferred embodiment;
Figure 2 shows various details of the
collector/desorber areas according to the preferred
embodiment; and
Figure 3 is an elevation view of the sampler/desorber
unit, disassembled, in its major components.
Detailed Description of the Preferred Embodiment
Turning to Figure 1, the sampler/desorber unit of the
preferred embodiment is shown comprising a fan 1 which is
driven by a fan motor 14A (Figure 3) for drawing air
through the unit, creating suction at the nozzle 2.
Particulates of all descriptions are drawn into the
collector/desorber area 3 and come to rest on a first metal
mesh tray card 4. This tray card is in direct contact with
a heater wire and screen assembly, which maintains it at a
temperature high enough to vaporize (desorb) the target
particulates.
Vapours from the desorption then pass through a second
metal mesh sample card 5, which is in a much cooler
environment than the tray card 4, so that some of the
vapours are caused to condense on the sample card. The
temperature of tray card 4 for causing desorption and the
temperature of the sample card 5 for causing condensation,
are each controlled so as to ensure as complete a transfer
of the target vapours as possible, while allowing the more
volatile material to pass through the system and be vented
at 6, and the less volatile material to remain
unvolatilized on the tray card.
The following table summarizes a list of optimum
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temperature of the sample card and tray card, to achieve
the above-mentioned objectives:
TABLE
Sub~nce S mpk C ld Tcmp~turc ~y Cut Holde
c~c 90-100 dc~ C 190 - ~0 dc~ C
Hcroin 89 -110 dc~ C 200 - 235 de~ C
THC 88 -104 dc~ C 190 - 200 de6 C
C4 (RDX) 90 - 110 de~ C 204 - 220 def C
PEIN 80 -100 de~ C 150 - 200 dc~ C
The indicated temperature ranges are for optimum
transfer of substance of interest, with minimum amounts of
decomposition.
Adherence of these substances to silica, dust, etc.
requires relatively higher desorption temperatures for
releasing these materials in the gas phase. In such
instances, the heater temperature is selected to lie in the
range of 235 - 260 deg. C. The compromise is lower PTN
transfer to the sample card, because PETN undergoes
decomposition at temperatures in the range of 150 - 200
deg. C. Under these higher desorption temperatures, only
a fraction of the PETN will be transferred to the sample
card.
The sample card 5 is then withdrawn from the desorber
area 3, and transferred to a suitable detector (not shown)
for a second desorption and analysis. One example of a
suitable detector is the Scintrex Model TND-100 Trace
Narcotics Detector. It is based on the principle of gas
chromatography and a nitrogen-phosphorous detector. Other
suitable detectoræ are the Ionscan unit of Barringer
Technologies (IMS technology) and the Sentor and EGIS
detectors of Thermedics, Inc., etc. The sample thus
provided to the detector is relatively clean.
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The tray card 4 may be withdrawn for cleaning, and the
collector/desorber chamber 3 is constructed so that it may
be readily opened and cleaned of the residues of the
sample, as and when required.
*Figure 2 shows some details of the collector/desorber
area 3, including the heater wire assembly 8, which is
heated by passing current through electrical contacts 9.
The tray card 4 contains a stainless steel mesh section 10
on which the original sample is collected and vaporized.
Figure 3 shows the preferred embodiment of Figure 1,
broken down into its mahor components, e.g. for replacement
of battery 7, and for cleaning of the collector-desorber
area 3.
The disassembly of the latter for cleaning is readily
accomplished by means of a thumb nut 11 which, when
activated, allows the quick removal of the nozzle and front
section housing of the collector-desorber chamber.
The sampler/desorber unit of the present invention
may be battery powered via a battery 7 for hand-held use,
or by mains power for other applications.
The unit of the present invention is suitable, for
example, to remote controlled entry into large shipping
containers and for hand-held checking of individuals,
clothing and luggage, etc.
Modifications and alternative embodiments of the
invention are possible within the sphere and scope of the
claims appended hereto.
