US3658481A

US3658481A - Flame ionization detector assembly

Info

Publication number: US3658481A
Application number: US25759A
Authority: US
Inventors: Claude Guillemin; Jean-Claude Badin
Original assignee: Produits Chimiques Pechiney Saint Gobain
Current assignee: Produits Chimiques Pechiney Saint Gobain
Priority date: 1969-04-11
Filing date: 1970-04-06
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25
Also published as: DE2017301A1; GB1297062A; FR2040735A5; BE748794A; NL7004779A

Abstract

A flame ionization detector assembly for use in gas chromatography including a detector and a gas sampling assembly comprising a housing defining primary passage means for gaseous effluent from a chromatography column, a needle and a valve seat, both of which are received in recesses defined by the housing and both of which define passages communicating with the primary passage means whereby a small portion of the gaseous effluent from the chromatography column passes from the primary passage means through the passages defined by the valve seat and the needle to a combustion zone.

Description

United States Patent Guillemin et al.

[ 51 Apr. 25, 1972 [54] FLAME IONIZATION DETECTOR ASSEMBLY [72] inventors: Claude Gulllemln, Paris; Jean-Claude Badln, Bondy, both of France [73] Assignee: Produits Chimique PechineyrSaint-Gobain,

Neuilly-sur-Seine, France [22] Filed: Apr. 6, 1970 [21] Appl. No.: 25,759

[30] Foreign Application Priority Data Apr. 11, 1969 France ..691l175' [52] US. Cl. ..23/254 E, 23/232 C, 23/232 E,

23/255 E, 73/23 [51] Int. Cl. ..G0ln 31/00, GOln 31/12,G0ln 27/62 [58] Field of Search ..23/255 E, 254 E, 232 E; 73/23 [56] References Cited UNITED STATES PATENTS 3,215,499 11/1965 Dewaretal. ..23/255 E 1/1966 Beroza .....23/230 3,399,974 9/1968 Spencer et al ..23/255 E 3,502,439 3/1970 Reece et al ..23/255 E Primary Examiner-Morris 0. Wolk Assistant Examiner-R. E. Serwin Attorney--McDougall, Hersh 8:. Scott ABSTRACT A flame ionization detector assembly for use in gas chromatography including a detector and a gas sampling assembly comprising a housing defining primary passage means for gaseous effluent from a chromatography column, a needle and a valve seat, both of which are received in recesses defined by the housing and both of which define passages communicating with the primary passage means whereby a small portion of the gaseous effluent from the chromatography column passes from the primary passage means through the passages defined by the valve seat and the needle to a combustion zone.

15 Claims, 1 Drawing Figure i Patented April 25, 1972 1 Gas Y B flv a A 5 FLAME XONIZATION DETECTOR ASSEMBLY This invention relates to flame ionization detectors, and more particularly-to flame ionization detectors suitable for use in separations by gas chromatography.

The detection of variations with time of the composition of the gaseous effluent from a chromatography column lead to a flame by detection of various peaks by means of ionization measurement of the flame is well known. In chromatography for purely analytical purposes, the flow of gaseous effluent is quite low, and thus the entire flow can be fed to the detector in which separation of the peaks can be achieved without the occurrence of streaks or overlapping.

However, in applications of gas chromatography in which gaseous effluent from the column is continuously subjected to analysis, sometimes referred to as preparative chromatography, the greater portion of the gaseous effluent is intended to be collected in the form of separated portions. For this purpose, apparatus heretofore employed have included various branch tubing in the outlet piping of the chromatographic column, flow control valves and connections to the flame detector, all of which contribute to a number of problems as a result of branch tubing processes and large dead volumes in the apparatus.'

The primary difficulties incurred through the use of apparatus of the type described involve a decrease in the acuteness or sharpness of the peaks detected by the ionization detector and the occurrence of disturbances in the gaseous effluent flow from the chromatography column, whereby the selectivity of the chromatographic apparatus is significantly decreased. in addition, because of the large dead volume of the apparatus, the variations in the composition of the main stream of the effluent flow from the column do not correspond to the image given by the detector, thereby making it impossible to efficiently program the separation of the various fractions.

it is accordingly an object of the present invention to provide a flame ionization detector which is capable of overcoming the foregoing disadvantages.

It is a more specific object of the invention to provide a flame ionization detector suitable for use with chromatographic separations having a minimum of dead volume so as to be capable of detecting sharp peaks without the occurrence of disturbances caused by too large a diversion of the primary gas flow.

These and other objects and advantages of the invention will appear hereinafter, and, for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the attached drawing in which the figure represents a cross section of a flame ionization detector embodying the features of the invention.

The concepts of the present invention reside in a detector assembly including a gas sampling assembly for use with a detector comprising a housing defining primary passage means for the gaseous effluent from the chromatography column, passage means for a fraction of the flow of column effluent, and a valve to control the flow of this fraction to the detector. This assembly can be used in conjunction with a conventional detector including a burner head, measuring electrodes, temperature measuring means, an ignitor and a protective bell to provide a flame ionization detector having a minimum of dead volume which is capable of detecting sharp peaks without the occurrence of disturbances caused by too large a diversion in the primary gas flow.

In the preferred form of the invention, the housing is in the form of a solid block, preferably formed of a metal, which defines the passage means therethrough as well as the recess for the glass flow control valve and the passages for the electrodes and other detector elements.

Refering now to the drawing, there is shown a device embodying the features of the invention including a block 1 forming the housing. The housing block 1 is preferably formed of a metal, such as stainless steel, and defines a passage 2 through which the primary gas flow from the column can exit from the device. The gaseous influent to the apparatus of the invention is fed to passage defined in flange 4 and annular element 3. Passage 25 communicates with passage 2 so as to define a primary tube or passage through which the primary gas flow from the column may pass.

Housing block 1 also defines a recess adapted to receive a valve seat member 6 having a passage 7 having a small diameter therethrough communicating with the primary tube defined by passages 25 and 2 which is maintained in its recess by means of the abutting relationship of annular element 3. The valve seat member 3 is preferably formed of a plastic material which is stable against chemical attack from the gaseous effluent of the column and thermally stable at the prevailing column effluent material. For this purpose, use is preferably made of a valve seat member formed of polytetrafluorethylene, although use can also be made of a variety of other materials.

Housing block 1 also defines a recess adapted to receive a coaxial needle 9 which extends through the recess, and is adapted to seat in valve seat element 6. As shown in the drawing, valve seat element 6 has a conical recess defined by surface 8 which is adapted to receive the corresponding conical end of needle 9 in a sealing relationship when the valve is closed. The upper end of needle 9 is threadably engaged with housing block 1 by means of thread means 12, and needle 9 is adapted to be displaced into sealing engagement with valve seat 6 by means of a gear wheel 17 fixed to needle 9 by way of block 13 which is actuated by an endless screw 18 which extends through housing 1 where it is accessible on the outside thereof to rotate needle 9 about its cylindrical axis and thereby displace needle 9 relative to valve seat member 6.

Near its lower portion, needle 9 is sealed from its recess by means of toroidal sealing means 10 whereby the conical surface of needle 9 and the corresponding conical recess of surface 8 of seat element 6 define a space therebetween when the valve is at least partially open. As shown in the figure, the space defined by needle 9 and surface 8 communicates on the one hand with passage 7 extending through seat member 6. The space also communicates with

passages

11 and 16 extending at least partially through needle 9 whereby gases are perknitted to flow through passage means 7 to the space defined by needle 9 and surface 8 and through passage means 11 and 16 to combustion chamber 26 defined by housing I. Since passage 16 extends into combustion chamber 26, tube 16 is preferably formed'of a refractory material such as fused silica or the like extending through a bushing 15 formed of a plastic material, such as polytetrafiuoroethylene. As shown in this figure, the lower postion of passage 11 is oblique relative to the axis of needle 9 and extends substantially perpendicular to the conical surface of needle 9 and to surface 8. However, a variety of other positions of the lower portion of passage means 11 are similarly suitable in the invention to feed a small amount of the effluent to the combustion zone.

Housing 1 also defines a passage 19 for the introduction of a fuel gas, preferably hydrogen, to combustion chamber 26 by means of tube 20 extending through a plastic bushing 21. Similarly, housing 1 defines passage means 22 for the introduction of an oxygen-containing gas such as air to combustion zone 26. While it is not illustrated in the drawing, the top of combustion zone 26 may be provided with a protective bell of the type conventionally used in flame ionization detectors, which may be threadably engaged with threads 23 and sealed by sealing means 24. Also not illustrated in the drawing for the sake of simplicity are the standard elements of a flame ionization detector including the measuring electrodes, temperature measuring means, such as a thermocouple, and an electrical resistance ignitor.

In use, the gaseous effluent from a chromatography column is fed to the primary tube defined by passages 25 and 2 whereby the gases flow therethrough. The needle valve is opened by causing shaft 18 to rotate, thereby turning wheel 17 and displacing needle 9 upwardly away from valve seat member 6 to define a space between needle 9 and surface 8 of valve seat member 6. This enables a small portion of the gas passing through passage 25 to pass through passage 7 in valve seat member 6 and through passage 11 in needle 9 and through tube 16 where the gas is contacted with a hydrogenoxygen flame in combustion zone 26. Ionization of the gas in the flame can then be measured by means of the electrodes in a conventional manner.

It will be apparent from the foregoing that the device of the present invention has a very small dead volume since it makes use of passage means having a small diameter and short length joining the primary gas flow and the flame. The quantity of gas samples can easily be regulated by displacement of needle 9 relative to valve seat member 6. However, it will be understood by those skilled in the art that the various elements are not restricted to the configurations illustrated in the drawing. For example, the tube for primary gas flow may be rectilinear or have a regular curvature instead of the right angle tube illustrated. In addition, it is possible to provide a tube having a small diameter extending into passage 2, preferably so as to be coaxial therewith, whereby a fraction of the column effluent may flow through this tube to passage 7 and to combustion zone 26.

It will be understood that various modifications and changes can be made in the details of construction and use without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. In a flame ionization detector assembly for use in gas chromatography in which a small portion of the effluent from a chromatography column is passed to a combustion zone for flame ionization, the improvement comprising a housing, said housing defining first passage means for gaseous effluent from a chromatography column, a needle and valve seat means, both of which are adapted to be received in recesses defined by said housing with the needle being mo'veable relative to the valve seat means to define a space therebetween when the needle is moved away from the valve seat means to an open position, said valve seat means including a small passage communicating with the first passage and said needle including an internal passage communicating with the combustion zone and the space defined between the needle and the valve seat means, whereby a small portion of gas passes from the first passage through the small passage of the valve seat means and the internal passage of the needle to the combustion zone, and passage means to supply an oxygen-containing gas and a fuel gas to the combustion zone.

2. An assembly as defined in claim 1 wherein said housing is in the form of a block.

3. An assembly as defined in claim 2 wherein said block is formed of metal.

4. An assembly as defined in claim 2 wherein said block is formed of stainless steel.

5. An assembly as defined in claim 1 wherein said valve seat means has a conical recess formed therein and said needle has a conical section on one end thereof, said conical recess being adapted to receive said conical section of said needle in sealing relation when said needle is in closed position.

6. An assembly as defined in claim 1 wherein said valve seat means is formed of a plastic.

7. an assembly as defined in claim 1 wherein said needle is threadably received in said recess in said housing, said needle being moveable in response to rotation in threaded engagement in said housing.

8. An assembly as defined in claim 7 which includes a gear wheel fixed to said needle and an endless screw engaged with said gear wheel, said needle being rotatable in response to rotation of said screw.

9. An assembly as defined in claim 1 wherein a portion of the internal passage defined by said needle is coaxial therewith.

10. An assembly as defined in claim 9 wherein the remaining portion of the internal passage defined by said needle is oblique with res ect to the axis of said needle.

11. An assem ly as defined in claim 1 wherein said passage means to supply fuel are defined by said housing.

12. An assembly as defined in claim 1 wherein said first passage means is formed by right angle passages.

13. An assembly as defined in claim 1 wherein said first passage means of rectilinear.

14. An assembly as defined in claim 1 wherein said first passage means is curved.

15. An assembly as defined in claim I wherein said assembly includes a detector including measuring electrodes, temperature measuring means and ignitor.

Claims

2. An assembly as defined in claim 1 wherein said housing is in the form of a block.
3. An assembly as defined in claim 2 wherein said block is formed of metal.
4. An assembly as defined in claim 2 wherein said block is formed of stainless steel.
5. An assembly as defined in claim 1 wherein said valve seat means has a conical recess formed therein and said needle has a conical section on one end thereof, said conical recess being adapted to receive said conical section of said needle in sealing relation when said needle is in closed position.
6. An assembly as defined in claim 1 wherein said valve seat means is formed of a plastic.
7. an assembly as defined in claim 1 wherein said needle is threadably received in said recess in said housing, said needle being moveable in response to rotation in threaded engagement in said housing.
8. An assembly as defined in claim 7 which includes a gear wheel fixed to said needle and an endless screw engaged with said gear wheel, said needle being rotatable in response to rotation of said screw.
9. An assembly as defined in claim 1 wherein a portion of the internal passage defined by said needle is coaxial therewith.
10. An assembly as defined in claim 9 wherein the remaining portion of the internal passage defined by said needle is oblique with respect to the axis of said needle.
11. An assembly as defined in claim 1 wherein said passage means to supply fuel are defined by said housing.
12. An assembly as defined in claim 1 wherein said first passage means is formed by right angle passages.
13. An assembly as defined in claim 1 wherein said first passage means of rectilinear.
14. An assembly as defined in claim 1 wherein said first passage means is curved.
15. An assembly as defined in claim 1 wherein said assembly includes a detector including measuring electrodes, temperature measuring means and ignitor.