GB2194742A

GB2194742A - Gas chromatography

Info

Publication number: GB2194742A
Application number: GB08717243A
Authority: GB
Inventors: Malcolm Cecil Trippe
Original assignee: British American Tobacco Co Ltd
Current assignee: British American Tobacco Investments Ltd
Priority date: 1986-08-06
Filing date: 1987-07-21
Publication date: 1988-03-16
Also published as: GB8717243D0; GB8619239D0

Abstract

The invention provides a method and apparatus whereby, during an operational run of a gas chromatography apparatus, the analytical column (2) of the apparatus is put into gas-flow communication with adsorption means (12) for the duration of a predetermined time window to capture a sample represented by a peak which occurs in said time window. The captured sample may be passed through a gas chromatography apparatus again and thence into a mass spectrometry apparatus for further identification. <IMAGE>

Description

SPECIFICATION Improvement relating to gas chromatography The subject invention relates to gas chromatography apparatus and to the operation thereof.

A chromatogram relating to an operational run of a gas chromatography apparatus comprises a number of peaks, each of which peaks represents a chemical compound or mixture of compounds present in the sample fed to the analytical column of the apparatus.

Quantitative information is available from a chromatogram, but of itself the presence of a particular peak does not provide the identity of the compound or compounds represented thereby. Identification requires the employment of further analytical techniques, as for example mass spectrometry. Thus it has heretofore been a practice to repeat the operational run with the analytical column having been taken to and coupled with a full size mass spectrometry apparatus or with the gas chromatography apparatus having been coupled with a bench top mass spectrometry apparatus. Neither of these procedures has been found to be wholly satisfactory, especially in cases where a peak under examination is a small one, that is to say when the compound or compounds in question is/are present in only a small quantity.

It is an object of the present invention to provide means whereby identification of a compound represented in a gas chromatography chromatogram may be made with endanced facility, even if present in only small quantity in the substance analysed by the gas chromatography apparatus.

The present invention provides gas chromatography apparatus comprising a sample flow outlet and mounting means at the region of said sample flow outlet, said mounting means being adapted for releasably mounting adsorption means in gas-flow communication with said sample flow outlet.

Preferably the sample flow outlet is in gasflow communication with the analytical column of the apparatus downstream of the full analytical extent of the column. Suitably the sample flow outlet is one at which is provided detection means operable to provide a signal from which a chromatogram is derivable.

By use of the present invention adsorption means can be mounted on gas chromatography apparatus for sample adsorption for the duration of a time window within which during a previous analytical run of the apparatus a particular peak occurred on a chromatogram generated for the run. At the end of the time window, the adsorption means is put out of gas-flow communication with the sample flow outlet of the apparatus. This is readily achieved by removing the adsorption means from the apparatus. Alternatively, the apparatus may be provided with valve means operable to switch the gas flow from a first path leading to the sample flow outlet to a second path by-passing the sample flow outlet.

Gas chromatography apparatus in accordance with the present invention may comprise housing means, a generally tubular housing for example, extending about the sample flow outlet. Advantageously, the mounting means engages with such housing means, by, for example, being received in or around the housing means.

The present invention is applicable to gas chromatography apparatus equipped with various detection means, as for example flame ionisation, electron capture or hot wire detection means.

The present invention further provides a method of gas chromatography, wherein during an operational run of a gas chromatography apparatus the analytical column of the apparatus is put into gas-flow communication with adsorption means for the duration of a predetermined time window to capture a sample represented by a peak which occurs in said time window.

The adsorption means, with the captured sample therein, can at any convenient time be coupled to a mass spectrometer apparatus, the sample then, while being heated, being swept into the apparatus in a stream of carrier gas. Preferably, the sample is carried to the mass spectrometer apparatus via a gas chromatography column.

Should the compound of which the identity is to be ascertained be present in the sample substance at a very low level, the adsorption means may be put into communication with the analytical column of the gas chromatography apparatus for the duration of the time window in each of a plurality of identical operational runs of the apparatus. In this manner a larger amount of the compound under investigation is accumulated in the adsorption means.

As used herein, the term "adsorption" embraces the concept of absorption.

In order that the present invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the diagrammatic drawing hereof, in which: Figure 1 shows, in section, outlet end parts of a gas chromatography apparatus as assembled for an operational run of the apparatus; and Figure 2 shows a view similar to that of Figure 1 with an adsorption tube mounted on the gas chromatography apparatus.

Reference numeral 1 designated part of a wall of a casing of a gas chromatography apparatus. A tube 2 extending through an opening in the wall 1 is at the upstream end thereof, to the left as viewing Figures 1 and 2, in gas flow communication with an analyti cal column (not shown) located in the casing of which the wall 1 forms part. At its downstream end the tube terminates in a jet nozzle 3.

Surrounding and spaced from that portion of the tube 2 extending externally of the aforementioned casing is a housing 4 of tubular form which is fixedly secured to the wall 1.

A tube 5 opens into the tube 2 for the purpose of feeding hydrogen gas, from a pressurised source thereof (not shown), to the tube 2. A tube 6 extends through an opening in the wall 1 for the purpose of supplying combustion supporting air, from a pressurised source thereof (not shown), to the interior of the housing 4.

The tube 2 is formed of a metal except for a short length 7 thereof, the length 7 being formed of an electrically insulating ceramic material.

There is shown in Figure 1 an electrode 8 of tubular form which is fixedly secured in, but electrically isolated from a central opening of a cap member 9 which is threadedly engaged with the housing 4 at the right-hand end thereof.

As may be observed from Figure 1, the electrode 8 extends over and is spaced from an outlet end portion of the tube 2.

In normal analytical operation of the gas chromatography apparatus sample material is carried through the tube 2 from the analytical column of the apparatus by carrier gas. Hydrogen flows into the tube 2 from the tube 5 and air flows into the interior of the housing 4 from the tube 6. The purpose of the supply of hydrogen and air is to maintain combustion of the gases upon emergence from the nozzle 3.

lonisation variations in the combustion zone occasioned by the passage therethrough of compounds -present in the sample substance are detected by means of an electrical circuit comprising leads (not shown) extending from the portion of the tube 2 downstream of the insulating portion 7 and from the electrode 8.

Signals deriving from the circuit are used to generate a chromatogram.

When it is required in accordance with the present invention to capture a sample relating to a chromatogram peak, the flame existing at the nozzle 3 is extinguished by discontinuance of the hydrogen supply from the pipe 5. The cap member 9, together with the electrode 8 carried thereby, is then removed from the housing 4.

There is next inserted into the housing 4 a sleeve 10 (see Figure 2), comprising an axial bore 11. Into the bore 11 is inserted adsorption means taking the form of an adsorption tube 12 comprising a metallic tube 13 in which are disposed two spaced apart metallic mesh containment members 14 and 15. Disposed between the members i4 and 15 is a body of particulate adsorption material which for the sake of simplicity is not shown.

Since the sleeve 10 is a close sliding fit in the housing 4 and the tube 13 is a close sliding fit in the bore 11, the adsorption tube 12 is accurately disposed in relation to the tube 2.

After the required sample has been captured in the adsorption tube 12, the tube i2 is removed from the bore 11 and is immediately coupled to a mass spectrometer apparatus for analysis of the captured sample. Alternatively, the tube 12 is hermetically sealed at each end thereof and put aside for analysis of the captured sample at a later time.

Claims

1. Gas chromatography apparatus comprising a sample flow outlet and mounting means at the region of said sample flow outlet, said mounting means being adapted for releasably mounting adsorption means in gas-flow communication with said sample flow outlet.

2. Apparatus according to Claim 1, wherein said sample flow outlet is in gas-flow communication with the analytical column of said apparatus downstream of the full analytical extent of said column.

3. Apparatus according to Claim i or 2, wherein valve means is provided operable to switch the gas flow from a first path leading to said sample flow outlet to a second path by-passing said sample flow outlet.

4. Apparatus according to any one of the preceding claims, said apparatus comprising housing means extending about said sample flow outlet.

5. Apparatus according to Claim 4, wherein said mounting means is received in or around said housing means.

6. Apparatus according to Claim 4 or 5, wherein said housing means is generally tubular housing means.

7. A method of gas chromatography, wherein during an operational run of a gas chromatography apparatus the analytical column of the apparatus is put into gas-flow communication with adsorption means for the duration of a predetermined time window to capture a sample represented by a peak which occurs in said time window.

8. A method according to Claim 7, wherein said adsorption means is in gas-flow communication with said column for the duration of said time window for a plurality of identical operational runs of said apparatus.

9. A method of mass spectrometry, wherein adsorption means, carrying sample captured by the method of any one of Claims 7 or 8, is coupled to a mass spectrometer apparatus for sample identification.

10. A method according to Claim 9, wherein said sample is swept, whilst being heated, into said mass spectrometer apparatus by a stream of carrier gas.

11. A method according to Claim 9 or 10, wherein said sample is carried to said mass spectrometer apparatus via a gas chromatography apparatus.

12. Gas chromatography apparatus substantially as hereinabove described with reference to Figures 1 and 2 of the drawing hereof.