U.S. patent application number 09/738543 was filed with the patent office on 2001-10-11 for method and apparatus for gas chromatography analysis of samples.
Invention is credited to Bremer, Ralf, Hoffmann, Andreas.
Application Number | 20010027722 09/738543 |
Document ID | / |
Family ID | 7932842 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010027722 |
Kind Code |
A1 |
Bremer, Ralf ; et
al. |
October 11, 2001 |
Method and apparatus for gas chromatography analysis of samples
Abstract
The invention relates to gas chromatography analysis of a sample
having components to be investigated and water contained therein,
which after thermodesorption is separated and analyzed, the
thermodesorbed sample being transferred by means of carrier gas
into a first polar separation column which retains higher-boiling
components and water and passes low-boiling components, the lafter
being led, past a branching point which leads, on the one hand, to
a second polar or non-polar separation column and, on the other
hand, to the non-polar separation column, to the non-polar
separation column in a fashion excluding access to the second polar
or non-polar separation column, after which higher-boiling
components and water are transferred to the second polar or
non-polar separation column in a fashion excluding access to the
non-polar separation column, water being eliminated upstream of the
second polar or non-polar separation column by means of
cryofocussing.
Inventors: |
Bremer, Ralf; (Oberhausen,
DE) ; Hoffmann, Andreas; (Duisburg, DE) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Family ID: |
7932842 |
Appl. No.: |
09/738543 |
Filed: |
December 15, 2000 |
Current U.S.
Class: |
95/82 ;
96/101 |
Current CPC
Class: |
G01N 30/461 20130101;
G01N 2030/143 20130101; G01N 30/468 20130101; G01N 30/12 20130101;
G01N 2030/383 20130101; G01N 30/466 20130101; G01N 2030/122
20130101; G01N 2030/128 20130101 |
Class at
Publication: |
95/82 ;
96/101 |
International
Class: |
B01D 053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 1999 |
DE |
19960631.5 |
Claims
What is claimed is:
1. A method for gas chromatography analysis of a sample after
preceding thermodesorption, in which the components to be separated
and water are contained, wherein the thermodesorbed sample is
transferred by means of carrier gas into a first polar separation
column which retains higher-boiling components and water and passes
low-boiling components, said low boiling components being led, past
a branching device which leads, on the one hand, to a second
separation column of the group of a non-polar and a polar
separation column and, on the other hand, to a third non-polar
separation column, to the third non-polar separation column in a
manner excluding access to the second separation column, after
which the higher-boiling components and the water are lead to the
second separation column in a manner excluding access to the third
non-polar separation column, the water being eliminated upstream of
the second separation column by means of cryofocussing.
2. The method of claim 1, wherein gas samples, liquid samples or
solid samples are analysed.
3. The method of claim 1, wherein the sample is cryofocussed
subsequently to the thermodesorption before it is transferred into
the first polar separation column.
4. The method of claim 1, wherein the sample is thermodesorbed when
located in an exchangeable sampling tube.
5. The method of claim 4, wherein the sample in the sampling tube
is collected in a thermodesorption device by leading through an
appropriate medium flow.
6. The method of claim 1, wherein the access to the third non-polar
and to the second separation column is pneumatically excluded.
7. The method of claim 1, wherein the access is switched over as a
function of time from the third non-polar to the second separation
column.
8. The method of claim 1, wherein the access is switched over from
the third non-polar to the second separation column as a function
of a signal calibrated to a retention time of a compound with a
lower retention time than water.
9. The method of claim 8, wherein the signal is calibrated to the
retention time of toluene.
10. The method of claim 1, wherein the access is switched over from
the third non-polar to the second separation column on the basis of
a detected water breakthrough at the first polar separation
column.
11. The method of claim 1, wherein furnaces for the third non-polar
and the second separation column are operated independently of one
another.
12. The method of claim 1, wherein the sample is imparted an
increased rate of flow upstream of the access to the first polar
separation column.
13. An apparatus for gas chromatography analysis of a sample,
comprising: a thermodesorption device for holding a sampling tube;
a first polar separation column being connected downstream of the
thermodesorption device; a branching device being connected
downstream of the first polar separation column; a non-polar
separation column; a second separation column being of the group of
a polar and a non-polar separation column; wherein said branching
device being switchable over between said non-polar separation
column; and a device for eliminating water which is connected
upstream of the second separation column.
14. The apparatus of claim 13, wherein a cryofocussing device is
arranged between the thermodesorption device and the first polar
separation column.
15. The apparatus of claim 13, wherein the device for eliminating
water comprises a cryofocussing device.
16. The apparatus of claim 15, wherein the device for eliminating
water comprises a cooling device and a heating device.
17. The apparatus of claim 16, wherein the device for eliminating
water accommodates a coolable metal tube which is surrounded by a
heating winding and in which a further sampling tube is located,
there being arranged between the metal tube and the further
sampling tube an annular gap which is connected to a gas exhaust
line to which a thermal conductivity detector is connected.
18. The apparatus of claim 13, wherein the device of the group
comprising a thermodesorption device and a cryofocussing device
comprising a cooling device and a heating device, there being
provided, in particular, a coolable metal tube which is surrounded
by a heating winding and in which the appropriate sampling tube is
located.
19. The apparatus of claim 18, wherein an annular gap which is
connected to a gas exhaust line is arranged in the device of the
group comprising a thermodesorption device and a cryofocussing
device between the metal tube and the respective sampling tube.
20. The apparatus of claim 13, wherein the sampling tube of the
thermodesorption device is exchangeable.
21. The apparatus of claim 13, wherein the thermodesorption device
and, if appropriate, the cryofocussing device can be separated from
the first polar separation column by means of a switchover
valve.
22. The apparatus of claim 13, wherein the device of the group
comprising a thermodesorption device and a downstream cryofocussing
device is connected to the first polar separation column by means
of a transfer capillary.
23. The apparatus of claim 13, wherein a column connecting piece
comprising a gas exhaust line is connected upstream of the first
polar separation column.
24. The apparatus of claim 13, wherein the branching device
comprises a central branching piece and two further branching
pieces which are interconnected by means of capillary adapters.
25. The apparatus of claim 24, wherein a monitor detector is
connected to the central branching piece.
26. The apparatus of claim 13, wherein a heatable transfer
capillary and a further heatable transfer capillary are located in
two separate furnaces.
27. The apparatus of claim 13, wherein a heatable transfer
capillary and a further heatable transfer capillary are located in
a common furnace.
28. The apparatus of claim 13, wherein the first polar separation
column is located in a dedicated furnace.
29. The apparatus of claim 13, wherein the first polar separation
column is located in the furnace.
30. The apparatus of claim 13, wherein the second separation column
and the third separation column are respectively located in a
furnace, respectively.
31. The apparatus of claim 13, wherein the second separation column
and the third separation column are located in a common
furnace.
32. The apparatus of claim 13, wherein the first polar separation
column, the second separation column and the third separation
column are located in a common furnace.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method and apparatus for gas
chromatography analysis of samples.
[0002] To use gas chromatography to investigate small quantities of
components present in gases or liquids, such as foreign substances
or pollutants or impurities, it is known firstly to enrich these in
order then to feed them into a gas chromatograph via an appropriate
feeding system. However, problems occur in this case when the
collected samples contain moisture such as is the case, for
example, when pollutants contained in the air are enriched, since
the moisture contained in the air is then also enriched.
[0003] However, water severely disturbs a gas chromatography
system, and likewise the analysis, in the case of which, for
example, a substantial loss in sensitivity occurs in the mass
spectrometer. The presence of water in separation columns alters
the retention time, doing so, specifically, as a function of
quantity and differently for different substances, thus creating
the need to eliminate this as completely as possible in order to
obtain reliable measurement results.
BACKGROUND OF THE INVENTION
[0004] It is known to eliminate the moisture which is present in
samples to be chromatographically analyzed by osmosis. However,
this has the disadvantage that polar components are also eliminated
in the process, while non-polar components remain essentially
uninfluenced. However, the elimination of polar components other
than water falsifies the chromatogram.
[0005] Also known are packed capillary columns which exhibit a
temperature-dependent adsorptivity with reference to water, so that
given appropriate setting, low-boiling components are passed while
higher-boiling components and water are retained.
SUMMARY OF THE INVENTION
[0006] It is an object of the invention to provide a method for gas
chromatography analysis of samples which permits reliable gas
chromatograms to be obtained from samples containing water.
[0007] It is a further object of the invention to provide an
apparatus for gas chromatography analysis of samples which permits
reliable gas chromatograms to be obtained from samples containing
water.
[0008] According to the invention a method for gas chromatography
analysis of a sample after preceding thermodesorption, in which the
components to be separated and water are contained, is
provided,
[0009] wherein the thermodesorbed sample is transferred by means of
carrier gas into a first polar separation column which retains
higher-boiling components and water and passes low-boiling
components,
[0010] said low boiling components being led, past a branching
device which leads, on the one hand, to a second polar or non-polar
separation column and, on the other hand, to a non-polar separation
column, to the non-polar separation column in a fashion excluding
access to the second polar or non-polar separation column,
[0011] after which the higher-boiling components and the water are
lead to the second polar or non-polar separation column in a manner
excluding access to the non-polar separation column,
[0012] the water being eliminated upstream of the second polar or
non-polar separation column by means of cryofocussing.
[0013] According to the invention, further an apparatus for gas
chromatography analysis of a sample is provided, comprising:
[0014] a thermodesorption device for holding a sampling tube;
[0015] a first polar separation column being connected downstream
of the thermodesorption device;
[0016] a branching device being connected downstream of the first
polar separation column;
[0017] a non-polar separation column;
[0018] a second separation column being of the group of a polar and
a non-polar separation column;
[0019] wherein said branching device being switchable over between
said non-polar separation column; and
[0020] a device for eliminating water which is connected upstream
of the second separation column.
[0021] By virtue of the fact that according to the present
invention use is made as a precolumn of a polar separation column
with a stationary phase, which water does not initially have the
effect of separating it preliminarily into two fractions,
higher-boiling components and water can be retained at the
beginning, while low-boiling components are passed. The low-boiling
components are separated on the non-polar separation column via a
pneumatically closeable bifurcation which leads, on the one hand,
to a non-polar separation column for gases and, on the other hand,
via a cryofocussing device, to a further polar or non-polar
separation column, whereupon after pneumatically switching over the
bifurcation the water with higher-boiling components is eliminated
in the region of the cryofocussing device, whereupon the
higher-boiling components are separated in the polar or non-polar
separation column downstream of the cryofocussing device. In
addition, in this case the water elimination with subsequent
separation and analysis of a sample, and the separation on the
further separation column with subsequent analysis of another
sample, can be carried out simultaneously.
[0022] In this case, not only gaseous but also liquid samples which
contain water can be taken automatically by means of the
apparatus.
[0023] Further objects, embodiments and advantages of the invention
will become apparent from the following description and the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The invention is explained below in more detail with
reference to a preferred embodiment illustrated schematically in
the attached illustrations.
[0025] FIG. 1 shows a diagram of a gas chromatography apparatus
according to the invention, partially in section.
[0026] FIG. 2 shows the diagrammatic design of an embodiment of a
thermodesorption device or cryofocussing device or a device for
eliminating water for the gas chromatography device of FIG. 1, in
section.
[0027] FIG. 3 shows a diagram of a design of a branching point for
the gas chromatography device of FIG. 1, in section.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] The gas chromatography apparatus illustrated in FIG. 1
comprises a thermodesorption device 1 for a sample contained in a
sampling tube 2, a carrier gas connection 3 and a gas exhaust line
4 being provided. A transfer capillary 7 leading from the
thermodesorption device 1 to a feed head 5 of a cryofocussing
device 6 can be heated by a transfer furnace 8 in order to avoid
material losses upon transfer from the sampling tube 2 to the
cryofocussing device 6. The cryofocussing device 6 comprises a gas
exhaust line 9. A transfer capillary 10a, 10b downstream of the
cryofocussing device 6 leads, if appropriate, via a switchover
valve 11 to a column collecting piece 12 of a polar separation
column 13 serving as capillary precolumn, the column connecting
piece 12 comprising a gas exhaust line 14. The switchover valve 11
also comprises several feed or discharge lines 11a-11d for
flushing, calibration or automatic sampling. The transfer capillary
10a, 10b is arranged in a transfer furnace 15 which can, if
appropriate, form a common furnace with the transfer furnace 8.
[0029] A branching device 16 is arranged at the end downstream of
the polar separation column 13, which exhibits stable properties
with regard to separation in the presence of water. Separation
columns 17, 18 are connected separately from one another to the
branching device 16, it being possible to exclude pneumatically the
access to in each case one of the separation columns 17, 18 via a
gas line 19, which can be charged with gas via a valve 20 or 21 and
a controller 22.
[0030] The separation column 17 is a non-polar separation column
which, in particular, operates according to the principle of a
micropacked column, and serves to separate low-boiling components.
The separation column 17 is connected to an analyzer A1.
[0031] The separation column 18 is a polar or non-polar separation
column with stable properties with regard to the separation of
polar components. The separation column 18 is connected to an
analyser A2. Connected upstream of the separation column 18 is a
device 23 for eliminating water, which comprises a carrier gas
connection 24 and a gas exhaust line 25 for the purpose of
eliminating interfering water. In this case, a thermal conductivity
detector 26 connected to the gas exhaust line 25 is used to monitor
the completeness of the elimination.
[0032] The polar separation column 13 can be arranged in a furnace
27 which can, if appropriate, form a single furnace with the
transfer furnace 8.
[0033] The capillary separation columns 17, 18 are preferably
arranged in the furnaces 28 and 29, respectively, but they can also
be arranged in a common furnace, if appropriate together with the
polar separation column 13.
[0034] The device 23, illustrated in FIG. 2, for eliminating water
comprises a cooling device, which can be formed by a Peltier
element, a cyrostat or a passage for liquefied gas such as liquid
nitrogen. In the exemplary embodiment illustrated, a housing casing
30 is provided with coolant bores 31 which can be connected to a
coolant source, the housing casing 30 accommodating a metal tube 33
which is surrounded by a heating winding 32 and for its part
accommodates the sampling tube 2. An annular gap 34 which is
connected to the gas exhaust line 25 is located between the metal
tube 33 and the sampling tube 2. The carrier gas connection 24
opens into the sampling tube 2 in the region of a feed head 35. The
separation column 18 is plugged into the device 23 for eliminating
water in such a way that it projects into the sampling tube 2.
Since the inside diameter of the sampling tube 2 is larger than the
outside diameter of the separation column 18, the interior of the
sampling tube 2 is also connected to the annular gap 34.
[0035] The thermodesorption device 1 and the cryofocussing device 6
can be designed in a fashion corresponding to the device 23 for
eliminating water, and so reference is made to FIG. 2 in each case
in connection with these devices. The design can be selected, for
example, to accord with DE 44 19 596 C1, but it is also possible
here to provide cooling by a Peltier element or a cryostat, while
consideration may be given respectively in this connection to a
heating cartridge for example in accordance with DE 198 17 017 A1.
However, if appropriate, the annular gap 34 and the gas exhaust
line 4 or 9 can be dispensed with, if appropriate, in the case of
the thermodesorption device 1 and the cryofocussing device 6 when
split-mode operation is not desired. The thermodesorption device 1
can be designed as in the case where sampling tubes 2 are to be
used such as described, for example, in DE 195 20 715 C1. Each of
DE 44 19 596 C1, DE 198 17 017 A1, and DE 195 20 715 C1 is
incorporated herein by reference, as are any English-language
equivalents thereof.
[0036] In the embodiment of the branching device 16 of FIG. 3, a
central branching piece 36 is connected to two further branching
pieces 37, 38 via capillary adapters 39 which, for their part, are
connected via the valve 20 or 21 and the controller 22 to the gas
line 19 or to the separation column 17 or 18, it being possible, if
appropriate, to connect the central branching piece 36 to a monitor
detector 40, in particular a thermal conductivity detector.
[0037] A sample contained in the sampling tube 2 is thermodesorbed
in the thermodesorption device 1 by controlled heating of the
sampling tube 2 by means of the heating winding 32. During
thermodesorption, carrier gas is fed into the sampling tube 2 via
the carrier gas connection 3, and led into the cryofocussing device
6 via the heated transfer capillary 7 for the purpose of
transporting desorbed substances, including water which is present.
Uniform feeding of carrier gas is maintained constant in this case
in each method step via a flow sensor with a controller. Since
thermodesorption is performed without splitting, the gas exhaust
line 4 remains closed and thereby pneumatically closes the access
to the annular gap 34.
[0038] Initially, the cryofocussing device 6 is closed off at the
end, if appropriate by means of the switchover valve 11, from the
column connecting piece 12, its gas exhaust line 9 is opened, for
example via a valve (not illustrated), and its sampling tube 2 is
cooled down to minus 150.degree. C. by appropriate cooling, for
example with liquid nitrogen, such that all the components of the
sample which are to be investigated, including the water contained,
are collected in the sampling tube 2 and thus enriched. Thereafter,
the gas exhaust line 9 is closed, while the sampling tube 2 is
heated up, while being monitored, to a temperature of, for example,
350.degree. C., by means of the heating winding 32, all the
enriched components leaving the sampling tube 2 of the
cryofocussing device 6 and now being led into the separation column
13 by means of carrier gas because of the open switchover valve 11
via the column connecting piece 12.
[0039] The preliminary separation into two fractions of the
separation column 13 is initially not influenced by water which is
present, and higher-boiling components and water are retained there
by interaction forces of different strength for a longer time than
low-boiling, essentially non-polar components.
[0040] In the first phase of the separation by the polar separation
column 13 in which the furnace 27 is at ambient temperature, the
low-boiling non-polar components, i.e. those with one to
approximately four or more carbon atoms, flow through the polar
separation column 13 virtually without a separation effect, and
subsequently through the branching device 16. The valve 20 is
opened in this case, and so the branching device 16 is
pneumatically closed towards the polar or non-polar separation
column 18, and the low-boiling non-polar components are permitted
to pass to the non-polar separation column 17 by means of a
controlled carrier gas flow. These components are separated in the
non-polar separation column 17 and analyzed in the analyzer A1.
[0041] In a second phase of the separation by the polar separation
column 13, the valve 20 is closed and the valve 21 is opened such
that the branching device 16 is now pneumatically closed off from
the non-polar separation column 17. The valves 20, 21 are switched
over in principle as a function of time, the switch over being
calibrated to a retention time of a specific compound, which is low
boiling by comparison with water, in the non-polar separation
column 17, for example to the retention time of toluene, but it can
also be performed earlier, if appropriate, when the monitor
detector 40 which reacts to water outputs a signal on the basis of
incoming water which has the effect of permitting access by
higher-boiling components and water on the basis of the now
reversed direction of the overall gas flow to the polar separation
column 18 via the device 33 for eliminating water, the polar
separation column 13 then being additionally heated via the furnace
27 in order to release all higher-boiling components and/or
water.
[0042] The device 23 for eliminating water permits higher-boiling
components to be separated from water in three phases.
[0043] In a first phase, the cryofocussing, the higher-boiling
components and water are collected and enriched--as in the case of
enrichment in the cryofocussing device 6. In a second phase, the
sampling tube 2 of the device 23 for eliminating water is heated by
means of its heating winding 32, the water being eliminated via the
open gas exhaust line 25. This heating is performed to a
temperature above the freezing point of water and below the boiling
point of water, preferably to a relatively low temperature of, for
example, 10 to 2020 C., this temperature being selected in such a
way that as little loss of components as possible results in this
case, but an adequate water vapor partial pressure is present. The
monitoring of the water content in the sample is performed in this
case by means of the thermal conductivity detector 26, which reacts
to the presence of water and is connected to the gas exhaust line
25. Once the water has been completely eliminated, the gas exhaust
line 25 is closed on the basis of a signal output by the thermal
conductivity detector 26, whereupon in the third phase the sampling
tube 2 of the device 23 for eliminating water is heated further in
a programmed fashion by means of the heating winding 32, and the
individual components are released again one after another and are
then led into the polar or non-polar separation column 18 in which
they are successively separated and analyzed in the analyzer
A2.
[0044] Water is eliminated in the device 23 for eliminating water
by virtue of the fact that its sampling tube 2 is heated by means
of the heating winding 32, and that, with the gas exhaust line 25
open, the carrier gas flowing past a fed sample containing water
flows to the polar or non-polar separation column 18 at the end,
averted from the feed head 35, of the sampling tube 2 of the device
23 for eliminating water, back to the gas exhaust line 25 through
the annular gap 34, and is thereby eliminated. This form of
elimination of individual components, also termed split-mode
operation, can also take place in the cryofocussing device 6 by
means of a gas exhaust line 9, which is open here, and in the
thermodesorption device 1 by means of a gas exhaust line 4, which
is open here. The gas exhaust lines 4, 9 and 25 each have a valve
which is opened, preferably pneumatically, by means of pressure
control during split-mode operation.
[0045] It is expedient for the sample to be introduced quickly in
the column connecting piece 12 on the basis of operation as a
consequence of a continuously open gas exhaust line 14 by means of
the flow velocity, thereby increased, in order in this way to
achieve a defined peak end (avoidance of peak tailing) with a
defined sharpness of separation. Thinning of the sample resulting
therefrom is generally acceptable.
[0046] A sample can be introduced into the thermodesorption device
1 by means of an exchangeable sampling tube 2. Instead of this, the
sample can, however, also be collected in the sampling tube 2 of
the thermodesorption device 1 by the sucked-in ambient atmosphere
during split-mode operation with the gas exhaust line 9 open, the
gas being eliminated via the annular gap 34 and the gas exhaust
line 9. If appropriate, the switchover valve 11 can, also be
arranged upstream of the cryofocussing device 6 in the region of
the transfer capillary 7.
[0047] The switchover valve 11 is adjusted after a passage of the
sample in such a way that firstly, with the aid of the now
connected feed line 11a and 11b the sample inlet is flushed up to
the outlet, and secondly, with the aid of the likewise connected
transfer capillary 10a, the feed line 11a and 11b, and also the
connected feed line to the carrier gas connection 3, the
thermodesorption device 1 and the cryofocussing device 6 are
flushed, while because of the closed exhaust line 14 the sample is
led further to the column interface 12 via the polar separation
column 13. Consequently, on the basis of the above circuit it is
possible to take a new sample in parallel with the sample to be
analyzed or to carry out a calibration of the thermodesorption
device 1 and of the cryofocussing device 6.
[0048] In a preferred embodiment, the separation columns 13, 17 and
18 are likewise arranged in individual furnaces 27, 28 and 29 such
that after passage of the respective sample the separation columns
13, 17, 18 are cooled down individually and prepared for the
subsequent sample, the temperature intervals being selected to be
smaller by the furnace 27, 28, 29, which is to be assigned
respectively to only one separation column 13, 17, 18, and cooling
taking place more quickly.
[0049] The pneumatic exclusion from the polar or non-polar
separation column 18 via the device 23 for eliminating water, or
from the non-polar separation column 17 is achieved on the basis of
switching over the valves 20, 21 and on the basis of the controller
22, which sets a higher flow velocity of the gas from the gas line
19 than is prescribed by the carrier gas flow which flows through
the polar separation column 13. The capillary adapters 39, which
have a diameter of 50 .mu.m to 100 .mu.m, for example, are to be
dimensioned in this case in terms of length and diameter and as a
function of the gas pressure used in such a way that no diffusion
takes place from the central branching piece 36 up to that one of
the two branching pieces 37, 38 which leads to the separation
column 17, 18 respectively not to be used.
[0050] While the invention has been shown and described with
reference to a preferred embodiment, it should be apparent to one
of ordinary skill in the art that many changes and modifications
may be made without departing from the spirit and scope of the
invention as defined in the claims.
* * * * *