Sample charger for a gas chromatograph

A sample charger for a gas chromatograph has a charging chamber constructed for connection to the separating column of the gas chromatograph and receives a sample container in the form of a tube by the lengthwise insertion of a rod-shaped sample holder which comprises a hollow insertion tube, in which the sample container is releasably secured at its forward end. The charging chamber and insertion tube have carrier-gas inlet openings so that the interior of the insertion tube and the sample container can be scavenged with inert gas during the insertion process and, after the sample container has been completely inserted into the charging chamber, the carrier gas flows through the container into the separating column.

FIELD OF THE INVENTION 
The invention relates to a sample charger for a gas chromatograph 
comprising a tubular desorption chamber having a connection at one end of 
the chamber for placing the interior thereof into communication with a gas 
chromatograph and being adapted to receive a substantially rod-shaped 
sample holder for introducing a sample container from the outside into the 
chamber. 
Chemical monitoring of harmful substances in the air, for example in 
factories, laboratories and the like is becoming increasingly important. 
Gas chromatographic techniques are often employed for this purpose. In 
such processes, samples are collected in adsorption tubes by pumping the 
air under examination through the tube for a certain time, during which 
the components of interest accumulate on suitable adsorbent material in 
the tube. The thus-enriched components are then thermally desorbed from 
the adsorbent and analyzed by gas chromatography. 
In gas-chromatographic analysis, it is essential to supply the sample 
correctly when inserting it into the gas-chromatographic separating 
column. One of the most important requirements is that the sample must be 
supplied under "inert" conditions, i.e. the adsorption tube must be free 
from air during desorption. This is advantageously achieved by scavenging 
with a suitable inert gas. 
PRIOR ART 
A sample charger for adsorption tubes now commonly used is described in 
"Gas-Chrom Newsletter", Volume 19, No. 2, March 1978 by Applied Science 
Laboratories Inc. However, this sample charger is not provided with a 
scavenging facility. Capsule-type sample chargers of this kind described 
e.g. in German Offenlegungsschrift No. 25 30 879 have proved to be 
satisfactory for introducing certain samples for gas chromatographic 
analysis. In these devices, a sample-holding capsule, firmly clamped to a 
rod-shaped holder, is introduced through a lock into a charging chamber 
and placed on a spike at the front end of the chamber. Known devices of 
this kind are simple, easy to handle and very advantageous in other 
respects, but unfortunately they are not suitable for use with adsorption 
tubes. 
OBJECT OF THE INVENTION 
An object of the invention is to provide a sample charger for a gas 
chromatograph which is suitable for charging adsorption tubes under inert 
conditions and which also is very simple to operate. 
SUMMARY OF THE INVENTION 
A sample charger in accordance with this invention preferably comprises in 
combination: 
a tubular charging chamber for receiving a tubular container for the test 
sample; 
connection means at one end of said charging chamber for placing the 
interior thereof into communication with the separating column of a gas 
chromatograph; 
at least one inlet adjacent said one end of said charging chamber for the 
admission of a carrier gas thereinto; 
a lock disposed adjacent the end of said charging chamber remote from said 
connection means, said lock including a lock gate operable to open or 
close said chamber to atmosphere; 
a sample holder for introducing the tubular sample container from outside 
through said open lock gate and into said charging chamber, said sample 
holder including an open-ended insertion tube for lengthwise insertion 
into said charging chamber; 
receiving means disposed at said one end of said charging chamber for 
receiving the leading end of said insertion tube in sealing engagement 
therewith and for placing the interior of said insertion tube in 
communication with the separating column of the gas chromatograph through 
said connection means; 
holding means disposed at said leading end of said insertion tube for 
releasably holding the forward end of said tubular sample container within 
said insertion tube, said leading end of said insertion tube being sealed 
by the sample container held therein; 
a passage between the inner wall of said insertion tube and the outer wall 
of said sample container held in said insertion tube for flow of carrier 
gas into the open end of said sample container remote from said holding 
means; 
at least one inlet adjacent said leading end of said sample holder for the 
admission of carrier gas from said charging chamber into said passage; and 
releasable means for holding said insertion tube in sealing engagement with 
said one end of said charging chamber.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawing, the sample charger illustrated is disposed on an 
assembly plate 1 which secures it to a wall W of a gas chromatograph 
around an opening therethrough. On the forward side of the assembly plate 
1 (i.e. on the left hand side thereof as viewed in the drawing), and 
located within the opening in the wall W, is a tubular charging chamber 7 
for receiving the sample holder, generally designated 13 and to be 
described in greater detail hereinafter. The forward end 24 of chamber 7 
is adjacent to a connecting member 8 for a gas chromatographic separating 
column 25a which passes through a plunger 9 and a screw-cap 10. As shown, 
the separating column 25a is preferably a capillary. 
On the side of the assembly plate 1 remote from the chromatograph is a 
lock, generally designated 5. Lock 5 comprises three housing parts, 
respectively designated 2, 3 and 4, and in the illustrated embodiment the 
central housing part 3 is integral with the tubular charging chamber 7. A 
lock valve or gate 11 is disposed in lock 5 and when in the closed 
position (not shown in the drawing), with the sample holder 13 withdrawn, 
seals the mouth of the chamber 7 from the atmosphere via an O-ring 18. 
A guide sleeve 6 for the sample holder 13 is disposed on a rearward tubular 
extension of the outer housing part 4, and has a connection 6a for 
scavenging gas. Rearwardly of the housing part 4, the sleeve 6 has a 
portion of reduced external diameter which is lined with a PTFE insert 16. 
A cooling coil 12 is disposed around the inner housing part 2 of the lock 
5. 
The arrangement so far described corresponds in principle with the 
capsule-type sample charger disclosed in German Offenlegungsschrift No. 25 
30 879 supra. 
The sample holder 13 essentially comprises an open-ended insertion tube 
force-fitted into a handle 15. For convenience, the forward part of the 
insertion tube is designated 14a. When inserted, as shown in the drawing, 
the insertion tube 14 is received by the guide sleeve 6, and passes 
through open lock gate 11 into chamber 7. The insertion tube 14 in its 
inserted position is sealed by O-rings 17 and 19. 
Holding means in the form of a screw-threaded nipple 20 are disposed at the 
front or chamber end 14a of insertion tube 14. Nipple 20 receives the 
forward end of a sample-containing adsorption tube 21 to hold it at the 
forward end of the insertion tube within the chamber 7, so as to leave a 
gap or annular passage 22 between tube 21 and the inner wall of tube 14 or 
the rear portion of the nipple. Adsorption tube 21 is open at both ends 
and its front portion and the front portion of the inner surface of nipple 
20 are both slightly conical, to ensure a good fit. In its received 
position, the front end-face of tube 21 is flush with the front end-face 
of nipple 20. 
The outer surface of nipple 20 has a conical ground surface and engages to 
give a tight seal with receiving means formed by a complementary conical 
ground surface 23 in the front wall 24 of chamber 7. Spherical ground 
surfaces or other sealing means could be provided instead of conical 
surfaces. 
The front end 24 of chamber 7 is formed with connection means for placing 
the chamber and separating column into communication in the form of a bore 
25 disposed so that the separating column 25a held by the screw cap 10 can 
be conveyed by the plunger 9 practically up to the mouth of the adsorption 
tube 21, thus greatly reducing the dead space between the sample tube 21 
and the beginning of the column. 
In order to ensure efficient but releasable sealing engagement between 
nipple 20 and the front end 24 of the chamber 7 during operation, sample 
holder 13 is resiliently pressed axially and inwardly by two spring 
gripping levers 26 and 27. The two levers, which are pivoted to sleeve 6 
and have springs 28a, are of any known kind and engage corresponding lugs 
28 on handle 15. 
The front of the handle 15 is constructed so that it exactly fits on the 
reduced diameter part of the guide sleeve 6. A groove and tenon 
combination on the handle and guide sleeve (not shown) is used to ensure 
that the handle, and consequently the insertion tube and nipple, connot 
rotate after the insertion tube has been completely inserted. This is to 
prevent damage to the very accurate conical ground surfaces on the nipple 
and in the front wall of the desorption chamber. 
A capillary 31 is coaxially secured by two spacers 29, 30 in the interior 
of tube 14 to the rear of the sample tube 21. Capillary 31 acts as a 
restrictor and also connects the interior of the front part 14a of tube 
14, in front of the forward spacer 29, to atmosphere. A 
pressure-regulating valve 35 or the like is connected to the outer end of 
capillary 31 for adjustment of the restrictor. 
Chamber 7 has a carrier-gas inlet or connection 32 slightly along from its 
end 24. At the same distance (when tube 14 is in the completely inserted 
position) are two carrier-gas inlet openings 33, 34 in nipple 20 which 
communicate with the annular space 22 between tube 21 and the inner wall 
of the nipple. 
In order to insert a sample into the gas chromatograph, the slightly 
conical end of sample tube 21 is inserted into nipple 20, which is then 
screwed onto the front end 14a of the insertion tube 14. As in the known 
capsule charging devices, the sample is then inserted by the sample holder 
through sleeve 6 and lock 5 into desorption chamber 7. During the 
insertion process, carrier gas is desirably supplied through inlet 32 and 
flows through the sample tube and valve 35 to the atmosphere, thus 
automatically scavenging the sample tube. The pressure during the 
insertion operation can be kept constant by suitably adjusting the valve 
or the restrictor. Annular space or passage 22 is simultaneously 
scavenged. After the insertion process is complete and nipple 20 is in 
tightly sealed engagement with front end 24, the carrier gas flows through 
opening 33 and 34 into space 22 and thence through sample tube 21 and bore 
25 into the separating column. 
Thus, it will be seen that, with the sample charger of this invention, both 
the sample tube and the surrounding cavities can be automatically 
scavenged with carrier gas during the insertion process, whereby the 
sample is supplied under inert conditions, in accordance with the best 
practice. No complicated manipulation is required for this purpose; it is 
only necessary, as in the known capsule systems, to insert the 
sample-holder and secure it by the gripping levers.