Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
3 ~
The present inventiol~ relates in general to a methocl
o~ high re~olution gas chromatocJraphy and in particular rel~-
tes to an improvcd method for conductincJ ~as chromatographic
separation o~ components of volatile sample mixtures and con-
venient concentration of eluted samples~ The method utilizes
elevated column pressure, controlled column flow rate and in-
cludes intermittent stop flow operation.
Gas chromatograph ins-truments and the gas chromato-
graph methods comprise a class of extremely sensitive devices
and methods for the séparation of components ~rom a volatile
sample mixture. Usual practice has been to mix the volatile
sample with an inert carrier gas, the mixture o~ which is then
percolated through a column containing granulated particles pro-
viding a large surface area. Depending upon the choice oE the
granulated packing material, a solid or liquid stationary phase
is interfaced with the mobil carrier and sample mixture gaseous
Phase- The sample mixture components are, in the percolating
process, partitioned between the mobil gaseous phase and the
stationary liquid or solid phase. Each component or, if poorly
resolved by the process, each class of component compounds will
exhibit a unique~rate oE travel through a given column reEerred
to as the retention timo for the oompound in the oolumn.
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i~8~73~
Heretofore extensive investigative work has been
conducted with temperature programming of chromatographic
columns and with various packing materials for columns
with a purpose to increase solubility of the sample mix-
ture in one or both the stationary phase and mobil gase-
ous phase. Comparable investigation work has not been con-~
ducted to date to examine the effect of increased low and
intermediate range column exit pressure, i,e., gauge pres- ` ;
sures measured at the coLumn outlet in the range of one
to fifty atmospheres gauge pressure on the efficiency and
operation of chromato-graph columns. Some earlier work at
, high pres9u~es, i,e., pressures in the L000 to 2000 at-
s mospheres (absolute) range~ has been conducted to separate
i, large molecular weight molecuIes, the earlier very high
~1 ` ! .
~,; pressure investigations depended upon the altered near
liquid like density of the carrier gas at extreme pressures
to heighten sampLe solubility in the gaseous phase and
facilitate separation of high molecular weight compounds.
From the a~oresaid high~pre9sure invs9tigations no readily
usable laboratory device or method for gensral purpose ~;
; chromatographic procedures within the pressure range of
one to fif~y atmospheres gauge was disclosed,
Usual practice has been to operate conventional gas
~;J~ ~ chromatographs at the column gas veloc~ity which optimizes
S~ the resolutlon and speed of operation for a specific sample
mixture. This ~procedure has been achieved by operating ,
~ the output opening of the column at atmospheric pressure,
'3 ~ and regulating the flow rate of carrier gas injected into
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1~8gL731
the column input opening from a pressurized tank.
Commonly, the pressuri7.ed cylindrical tank reservoir of
carrier gas is held at pressures above 200 atmospheres.
In conventional gas chromatograph laboratory practice dur~
ing operation~ the pressure within the column in the vi-
cinity of the carrier gas input opening is between one
and ~hree atmospheres gauge pressure, By adjusting the
carrier gas inpu~ flow rate, the carrier gas velocity with-
in a specific coLumn may be adjusted to achieve the reso-
lution and sample separation desired. The pressure drop ,~
between the input and output regions of conventional
chromatograph column usage ranges between one and three
atmospheres. Accordingly, the gas velocity in the column
is substantial due to the pressure drop forces aLong the
i,length of the column. Under these conditions, any sudden
. . . .
change in the gas pressure or gas velocity at the column
outlet opening such as may be induced in conventional
, . .
sample collection procedures may produce mixing within the
column and reduce the resoIution and separation of follow~
ing separa~ed but still entrained components,
Conventional gas chromatograph laboratory practice, in
order to achieve rapid highly resolved separations, utilizes '~
higher as distinct from lower carrier gas velocities with-
in the column to reduce time the purified sample entrained
in the lower portion of the column may be exposed to dif-
~- fusion. Only wlth relatively high carrier gas velocities
within the column can less mixing in the lower portions of - ;~
the column in the vicinity of the column outlet opening be
achieved under conventional column pressure ranges. By
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conventional columl~ pressure we mean column pressure,
measured at the column outlet opening, equal to atmospheric
absolu~e pressure or zero gauge pressure.
The high gas velocity in the chromatograph column
causes some difficulty when the emergent separated compo-
nents must be confined in a container ~or later analy9is
or use Separated and entrained sample components within
the column moving at rapid velocities l'pile up" if the
column is stopped or restricted in a transient manner for
purposes of segregating a sample component as it leaves ''
the column Moreover, in chromatograph columns as conven- ``
tionally operated, a pressure of approximately one at-
mosphere (absolute) prevails in the vicinity of the outlet
opening. When the column is operated in a stop flow mode,
.~ . . ~ . .
` the'rate of gaseous diffusion is sufficiently high at the ~ ~
.
.
relatively low one atmosphere (absolute~ exit pressure ~hat
'~ the separated and entrained components of the sample mix-.. ~ ~
~i ture hel'd in any extension of the column Eor storage are
,
rapidly mixed by diffusion and the resolution or separation `` ' '
.,~ .
''' ' between them is degraded. That is~ a separate and pure
,
!,,' ` sample component becomes contaminated with diffusion of -
other components of the sample from within the column or `''
' any extension of the column.
'` It is desirable to perform spectral and other analysis
I ~ on eluted pure sampIes emitted from a gas chromatograph. An
on line" arrangement is most convenient for the operator.
~!
'~' However, in such arrangement, the time for cycling the
~,
spectral analysis procedure must be coordinated with the
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47
clifference in retention times oE varlous sample compo- !~
nents leaving the chromatograph column. Spectral analysis
procedures such as infrared spectroscopy normally require
more ti~e than the dif~erence in retention times of several ~;
separated compounds passing through a chromatograph column,
The same condition characterizes other spec-tral analysis
methods such as, for instance, mass spectrometry, ultra
violet and visible band spectrometry, Raman spectrometry,
and nuclear magnetic resonance; also a similar condition
characterizes analytic procedures that are not spectral,
such as electromechanica~, polarographic and coulometric
analysis. Present laboratory practice reconciles the di~-
ferences on the one hand of the time oE response of chro-
matographic separation processes, and on the other hand, ` '
~., .
the normally much slower response time of spectral and ~'
certain other analysis processes by one of two methods,
neither of,which is completely satisEactory.
First, some spectral analysis are done on the fly, ,,
The fly scan method, necessarily only one rapid scan, fails,
to extract the optimum spectral analysis data'Erom the mov- '
ing purified sample. Valuable data is often lost. The fly
scan method, however, avoids disturbing the gas flow
emitted from the column outlet opening and the att,en,dant
mixing in the gas stream due to pressure disturbance that ~'
may be reflected back into the column which stop flow oper- '
ation is conventional existing devices would certainly cause. ~ `
The second method in current practice is that of stor~
~, ,
ing in a detachable container a pure sample of the eluted '~
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` ~L0~473:31
material~ issuing from the outlet of the chromatograph
column. This latter approach minimi~.es but does not avoid
the disturbance of the gas flow in the colutnn with its
attendant mixing wi~hin ~he operating columrl It may expose
the pure samples to outside contamination sources When
the sample is stored, it is possible ~o scan repeatedly with
the spectral analysis device and obtain the optimal spectral -
analysis data.
Conventional practice furnishes the purified sample to
the storage chamber at a pressure of one atmosphere. Some
spectral analysis procedures, such as infrared spectroscopy
requires that ~he sample be concentrated before analysis,
thus requiring still another step with the attendant added
costs, time and contamination risks.
The most convenient manner of achieving the required
time coordination between a chromatograph and a spectral
analysis device is to operate the chromatograph column in a
stop flow mode, provided this can be achieved without reduc-
ing the resolution and separation o~ subsequent entrained
components.
Hereto~ore, no chromatograph methocl or required clevice ,
has been available which provided low velocity control of the
: ~.
., ~
: carrier gas moving through a gas chromatograph column while
superior resolution of separated sample components was
maintained. Similarly, heretofore, no chromatograph method
and required device has been available with which stop
. ~ . ~ . .
flow mode of operation could be conducted and good separa- ~
.
tion of eluted pure materials maintained
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It is a irst object of the present invention to pro-
vide an improved high resolution general purpose gas chromato-
graph method~
It is another object of the present invention to pro-
vide an improved general purpose gas chromatograph method in
which the velocity of the carrier gas moving through the column
may be controlled and caused to move at very low velocities
without loss of separation and resolution of the purified and
eluted components.
It is still another object of the present invention
to provide an improved general purpose gas chromatograph method
suitable for direct in line operation of a suitably pressurized ;
gas chromatograph with any of a variety of spectral analysis
devices wherein the rate of emission of purified compounds from
the chromatograph may be adjusted to the rate of operation o
a spectral analysis device.
Still another object of the present invention is to
- provide an improved general purpose sensitive gas chromatograph !:
method which facllitates stop flow operation.
And still another object of our invention is to pro-
; vide an improved general purpose gas chromatograph me-thod in
which the pressure and concentration of purified sample
compounds, emitted from a suitably pressurized gas chromato-
graph column, is sufficiently high that no intermediate step
to concentrate the purified samples is required prior to i~
performing spectral analysis procedures on the samples.
According to the present invention, there is provided
a method for high resolution gas chromatography comprising the
,1 steps of passing a stream of carrier gas combined with a vapor
sample~mixture through a column at normal operating pressures
:! .
and velocities, and intermittently stopping the flow of gases
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with valye means jus~ax~ ed to the column outlet, wherewith
eluted but en-trained sample vapors, are held ~or brief intervals
during stopped flow within the packed column, whereby subsequent
eluted samples entrained within the column may be intermi-ttently
briefly retained during sto~ flow without appreciable diffusi~n
and remixing.
These and other objects and advantages of'the prese~-t
invention w-ll appear from the following description having re-
ference the attached nosl limitative drawings, wherein:
Figure 1 : shows a gas chromatograph accordiny to
the present invention;
Figure 2 : is a schematic graph of a van Deemter
plot;
i Figure 3 : is a schematic chart illustrating an im-
; proved chromatograph peak shape according -to the present inven-
tion;
Figures : 4, 5 and 6 show chromatogram of a stop flow
operation at various pressure conditions.
Referring to Figure 2 a schematic graph of a van
20 Deemter plot is shown wh;ch displays on the vertical axis the
inverse of the number of theoretical plates and on -the horizon-
tal axis the gas velocity in a chromatoyraph column~ 'rhe van
,~ Deemter plot is commonly used in a gas chromatography art and is
described in numerous publica-tions. The quantity N, or number
of theoretical plates, is a widely known figure of merit for
~ ' comparison of the efficiency of chromatograph column performance. ''
', We have observed that with successively higher column
' pressure a greater value of N, number of theoretical plates for
` a given chromatograph column,may be achieved. This is illus-
, . .
trated by the family of curves shown in the chart of Figure 2.
Each curve represents performance of a given column at the in- '
. ' '.
~ 8 ~
731
dicated pressurc as ~as velocity within the columrl is varied.
It is evident that the best efficiency,that is tlle la~-~est
value oE N, is achieved with increasing pressure with simulta-
neous reduction in column yas velocity.
We also observed that the resolution o the samples
tested improved with increased column pressure and increased
retention time, Tr. Figure 3 is a schematic chart illustratlve
of the improved chromatograph peak shape with increased pres-
sure and increased time of retention. The time of retention
is inversely proportional to column gas velocity. The highér
resolution peaks or improved peak shapes are narrower at the
base.
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~' ~! ' ' ' ' ' ' ' ' ' "" ' ' ' ' ' ' ' ' ' ' ' ' " ' ' ' ' :
'i' " ' ' ' : ~ ',' ' . ........ . .. .
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1~134733L
The experimental results,illustrated in Figures 2
and 3,demonstrate the feasibility of our improved method
wherein we pass a sample to be eluted through a-chromato-
graph coLumn, the col.umn being maintained throughout its
length at a pressure above one atmosphere absolute,and we
maintain a sufficiently small pressure drop along the column
to limit the column gas velocity to a small value The
point of the mo~t efficient separation takes place in the
Figure 2 illustrations at the minimum values of the curves
shown point A for the 250 psi curve, B at the 200 psi
curve and D at the 45 psi curve.
A device Ln which chromatographic separations may be
conducted at eleva~ed pressures using our me~hod is shown
in a schematic illustration in Figure L. A pressure re- ;`
: sistant chr~omatograph column 10 is shown having an inlet
opening 12 and an outlet openin~ 14. The column 10 may be
packed with any of a variety of granular stationary phase :
~ materials 16~ many o~ which are known and available to
.~ those familiar with chromatographic laboratory procedures.
~he column 10 is normally operated ln a thermally insulated
chamber or oven 18 in which the temperature of the column
may be closely controlled
;;: An injection port 20 is mounted to the column inlet
opening L2. The injection port is comprised of a heavily
walled chamber 22 which may be heated from an external
source not shown in the illustratLon to adjust the carrier
gas temperature before introducing it into the column 10.
An inner chamber 24 is mounted within the heavily walled
9 ~
~ . ~k
4~ 3~
chamber 22. The outlet end of the inner chamber 24 is
connected to the inlet opening 12 o:E the column 10. The ~.
inner chamber 24 is provided near its upper end with a
plurality o~ small apertures 26 which communicate between ;
the interior of heavily walled chamber 22 and the interior .: - .
of the inner chamber 24 through which carrier gas may be ~ ~-
caused to flow through the inner chamber and be introduced .~
..:. . . .
through the inlet opening 12 into the column 10. '~
The upper end of the inner chàmber 24 is sealed wlth
a septum 30. The septum is a self-sealing body, through ..~
which smalL samples of gaseous or readily volitized mixtures
. may be injected into the system for elution or separation.
.: The septum 30 is firml~ sealed in place with a threaded
cover 32, ~n aperture 34 is provided in the septum seal .
. cover 32 through which analysis samples may be inserted,
The carrier gas is conveniently retained at relatively
,
high pressure in a cylindrical tank reservoir 40, Pres-
sures in commèrciàlly available cylinders of compressed :~
gases such as purified nitrogen~ carbon dioxide, heLium, - ~,
argon and other commonly used chromatograph carrier gases
i9 normally available up to 200 atmospheres, The carrier
gas reservoir 40 i$ connecte~ through pressure resistant /
tubing 42 to the interior of the injection port heavily
walLed cham~er 22. A flow rate meter 44 and a pressure ~.
gauge 46 is connected to the pressure line 42. ~An adjust~
able flow regulation valve 48 controls the quantity of
carrier gas passed into the injection.port and into the
chromatograph column. A pressure reduction valve 49
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~3473~
reduces ~he pressure o~ the carrier gas to a predetermined
value as it is passed into line 42.
A thermal conductivity detector 50 having a tempera-
ture controlled chamber 52, input.and output openings 54
and 56, respectively, and an electronic sensing means 58.
A thermistor connected through an appropriate circuit, not ~
shown in the illustrations, will sensitively detect any .; :
change in thermal conductivity of the gas present in the
chamber 52. Conversely stated,.the detector will detect :~
a change in composition o~ gas flowing through the detector
chamber 52 due to different thermal conductivity oE the
varied gas composition, The sensor output voltage may be
displayed graphicalLy in a moving chart recorder 62, The .;~
input opening 54 of khe detector is connected through a ':',.,
. ~ .
, pressure resistant line 64 to outlet opening 14 of column.
; . , ,
stop valve 65 is inserted in the line 64, preferable ;~
- ..
juxtaposed to the column outLet opening. In all events,
the stop vaLve 65 is mounted so that negligible open volume
remains.within the conduit or tube connected between the
column outlet 1~ or the solid/liquid stationary phase
packing within the column, and the stop valve 65, The stop
valve 65 is preferably a quick response valve, That iS9 ',
rapid closing and rapid~opening action is achieved with ~ .
small rotation of the valve stem, The valve 65 may be.oper- :
ated at times under substantial pressure conditions, there~
fore, a pressure resistant valve design is required, '
An adjustable flow restrictive valve 70 is connected : ;
on the first or inlet side~to the output opening 56 of the ~
: ' ' ~ -' '~
, . .
)8~73~
detector through a pressure resistant line 60 and through
a sample collection chamber 68 and connected on the second -~ -
or outlet side to a stop valve 76. The stop vaLve 76 is
vented to atmospheric pressure A stop valve 61 is mounted
on the line 60. The flow restrictive valve 70 may be a
conventional pressure resistant needle valve comprised of
an axially movable needle valve stem 72 which seats onto a
beveled valve seat 74 The flow of gases through the flow
restrictive valve may be adjusted to create any desired
pressure in the vicinity of the column outlet opening
greater than atmospheric pressure up to the upper pressure
limits of the system. A pressure meter 66 connected to
line 60 provides in~ormation of pressure at the column out-
let 14. There is substantial resistance to gas ~lowing
through the column between the inlet 12 and the outlet 14.
, .,~ . .
.... .
'3' ~ ~ However, there is normally negligible resistance to gas
flow between the column outlet 14 and the flow restrictive
valve 70, therefore, the pressure within the system :~
measured at the gauge 66 adjacent to the flow restrictive
valve 70, will be representative o~ the pressure within
the column at the outlet opening 14. -
Our invention achieves to a significant extent the .
im~roved advantages described above such as highe-r resolu-
~ ~,
l tion and stop flow operation without loss of resolution for
`, ~ most volatile sample mixtures at column exit pressures as
'.,', ~ . ~;
^~ low as 45 psi~absolute. Scme volatile sample mixtures are -more difficult to s~eparate and require a larger concentrated
sample for later spectral analysis. Column exit pressures
,, :
8~73~
of 50 atmospheres gaug~ and higher may be required.
The gas chroma~ograph ilLustrated in the drawings has been
constructecl to operate safely at up to 50 atmospheres
gauge column exit pressures. Operation at higher ~han 50
atmospheres gauge pressure provided the carrier gas re-
mains in the gaseous state would not be inconsis.tent with
the lntent and purpose of our inven~ion.
Referring to the gas chromatograph system ilLustrated ;.
in Figure 1, typical operation utilizing our method is as
follows: carrier gas is caused ~o flow through the injecti~n
port 20 at a preselected pressure ranging, as shown on
gauge 46, between one atmosphere and Eifty. The pressure
reduction valve 49 readily permits the operator to establish
a steady state pressure in the carrier gas flowing through
.~ , .
pressure line 42. Any pressure, less than that present in
the carrier gas reservoir tank 40, may be used. The quan- ~
; tity of car~ier gas flowing in line ~2, may be adjusted by ~ :
flow control valve 48 and measured by the flow rate meter
The ~low resistance value 70 is then.ad~justed to fix
the column exit pressure, as observed on gauge 66 to any
pr.eselected valve between zero and fifty atmospheres or
more. When the gauge 66 indicàtes zero gauge pressure,
the chromatog~aph Ls being operated in the conventional
~: manner... Our invention relates to a gas chromatograph
method for operation above zero column exit gauge pressure.
Velocity o~ flow throug.h the column 10 and detector `~:
~ 50 may be regulated at column exit pressures greater than
.~ J3
', '
. , . : . ; . . .
3~
' zero gauge pressure by adjustments of the ~low rate
valve 48. At higher column pressure, very low gas velo- - ;
city within the column may be attained without 109s 0
chromatographic resolution.
Intermi~ten-t stop flow operation of a chromatograph
may be achieved with the closing of stop valve-65. ELuted -'
. . .
but entrained sample vapors, when valve 65 is closed, are '~ ;
held within the lower portion of the packed column 10. It
is important to avoid altering the "peaked" quality of the
eluted samples, that the valve 65 be actuated with a quick" ,~
` ~ response. Some "stop flow" capability in a conventional
. ~
~ chromatograph operated at conventional pressures and gas ;, ~'
', velocities may be demonstrated by utilizing a quick action ~
' , .................................... . .
valve mounted juxtaposed to the column outlet opening. ~ '
,' , Stop Elow operatiOn is preferably achieved by u~
, . ., .~ -
~, . .
,, zing a pressurized system equipped with a valved sample
, chamber. Stop flow is implemented by simultaneously
cLoslng the flow rate valve 48, the vent stop valve 76 ~ '
and the stop valve 65. Stop flow operation without 109s ~ :
; .
~ ~ of resoLut:ion o the remaining entrained'sample components
" ,
"i may be readily attainecl if the valves 489 76 and 65 are
closed on a slow moving rather than a rapidly moving gas r
~, ~ , flow. When the system is pressurized, the stop flow action ,
,;
,,
' is more readily implemented; the samples are more,com- ~ '
, l .
,,~ pletely separated and according to our pressurized method ` ~ ~
.,~; . , ~
~ may be entrained for longer periods of time without'diffu- ~ '
, ' ~
~ sion while being held stationary within the chromatograph.' ~
, .......... . . .
~ " - a~s - ,;:
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73:~
Samples may be concentratecl at whatever pressure the
operator may desire by making appropriate adjustments in
the pressure recluction valve 48 and simultaneously the
flow restriction me~ns 70, The samp]e pressur~ chamber '
will collect selected samples with our arrangement at the
pressure at which the chromatograph separation is conducted,
Pressure within the sample chamber may be read on pressure
gauge 66 which pressure will also be the pressure at the ''
column exit 14,
' Speci~ic examples of application of our method to stop
flow opera~ion of the chromatograph illustrated in Figure 1
at various pressure conditionsare ilLustrated in the graphs
shown in Figures 4, 5 and 6, The graphs show detector
voltage in millivolts on the verical axis9 and time in
minutes on the ho,riæontal axis.
Figure 4 is a chromatogram of stop flow operation with
the flow restriction means 70 open. The column exit pres- ~
sure was consequently zero gauge pressure as obs~rved on ~ ;
the gauge 66. The column had been stopped by closing stop ~
. , .
valve 65. When stop val.ve 65 is suddenly openecl~ the '~
eluted samples moved quickly past the detector 50 and left .'' ~,
~ a chromatogram wi~h poorly resolved crowded peaks. Poorly `~
; concentrated and crowded samples are difficult to scan with
any spectral analysis device, The samples at conventional
column pressure and column velocity are not fully separated.
::
' , Figure 5 is a stop flow chromatogram prepared with the
: , : .
column exit at 100 psi gauge pressure, Gas velocity in the
column had been significantly slowed. The samples are well
,' ' '. ;
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separated. Sample concentration is significantly superior to that
shown in Figure 4 prepared at zero gauge pressure at the column exit~
Notwithstanding the superior results achieved with our pressurlzed
stop flow method, our stop flow method at normal operating pressure~ I -
, that is, at atmospheric column outlet pressure is an advance over
~ present practices and is useful when pressur7zed equipment is not
; available.
Figure 6 is a stop flow chromatogram prepared at column exit ~
pressure of 180 psi gauge. The five components of the sample mixture ~.
are well separated; all samples are sufficiently concentrated so that
the indicator was saturated. Additional concentration of the individual
- ''l; ~
~samples prior to making a successful infrared spectroscopy test
was not required.
The forego7ng descrlptions of preferred examples of our method
,invention are intended as belllg lllustrat7ve only; the scope of our
InventTon Is set forth below 7n cla7ms. ~
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