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Claims for Patent: 5,242,471

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Claims for Patent: 5,242,471

Title: Coupling capillary gas chromatography to traditional liquid chromatography detectors
Abstract:Apparatus and methods are provided for using a detector designed for use with liquids to detect resolved analytes in an effluent stream from a gas chromatography instrument. The gaseous stream is entrained by a flowing liquid solvent, and at least a portion of the analytes are transferred from the gas phase to the liquid phase. The liquid solvent containing the analytes is then conveyed to a detector designed for liquid analysis. Thus, the present invention gives the analyst more options for detecting an analyte or a group of analytes, thereby providing greater flexibility in optimizing the sensitivity or selectivity of the analysis. Furthermore, the present invention allows gaseous effluents to be analyzed by detectors which more readily permit sample recovery than the detectors currently being used to analyze gaseous effluents.
Inventor(s): Markham; Dan A. (Rhodes, MI), Langvardt; Patrick W. (Midland, MI)
Assignee: The Dow Chemical Company (Midland, MI)
Application Number:07/887,996
Patent Claims: 1. A method of detecting resolved, structurally distinct analytes in a gaseous effluent stream from a gas chromatography instrument, comprising the steps of:

(a) forming a liquid-gas stream by entraining the gaseous effluent stream with a stream of liquid solvent such that the analytes retain their structural distinctiveness and generally retain the resolution achieved by the gas chromatography instrument; p1 (b) allowing at least a portion of the analytes to be transferred from the gaseous effluent stream to the liquid solvent stream;

(c) conveying the liquid solvent stream containing analytes from the gaseous effluent stream to a detector designed for liquid analysis which is responsive to the presence of the analytes; and

(d) detecting the distinct analytes.

2. The method of claim 1 wherein the gaseous effluent is maintained at a temperature sufficient to prevent the analytes resolved by the gas chromatography instrument from reuniting.

3. The method of claim 1 wherein the stream of liquid solvent is formed using a pumping means.

4. The method of claim 1 wherein step (a) includes directing the gaseous effluent stream to one arm of a tee and pumping the liquid solvent stream into another arm of a tee, such that the resulting liquid-gas stream flows out of a last arm of the tee.

5. The method of claim 1 wherein step (b) is facilitated by forming a segmented liquid-gas stream in step (a).

6. The method of claim 1 wherein the gas chromatography instrument includes a capillary column.

7. The method of claim 1 wherein the solvent contains a scintillating material and the detector is a liquid radioactivity monitor.

8. The method of claim 7 wherein the solvent is acetonitrile and the scintillating material is a liquid scintillation cocktail.

9. The method of claim 1 further comprising degassing the liquid-gas stream in between steps (b) and (c).

10. The method of claim 1 wherein the solvent contains a derivatizing agent effective for quickly reacting with the analytes forming a product which is more readily detected by the liquid chromatography detector.

11. The method of claim 1 further comprising the step of heating the region in which the liquid-gas stream is formed.

12. A chromatographic apparatus for separating and detecting structurally distinct analytes in a sample comprising:

a gas chromatography instrument for separating a sample into structurally distinct analytes in a gaseous effluent stream;

means for entraining the gaseous effluent stream from the gas chromatography instrument in a stream of liquid solvent such that the analytes retain their structural distinctiveness and the losses of resolution and chromatographic efficiency achieved by the chromatography instrument are minimized; and

a detector capable of analyzing liquids in fluid communication with the means for entraining the gaseous effluent stream in a stream of liquid solvent.

13. The apparatus of claim 12 wherein the means for entraining the gaseous effluent stream from the gas chromatography instrument comprises:

a mixing means having a first and a second inlet ports and one outlet port;

a first conduit means connecting the exit line of the gas chromatography instrument with the first inlet of the mixing means;

a means for delivering the flow of a liquid solvent;

a second conduit means connecting the means for delivering the flow of a liquid solvent to the second inlet of the mixing means; and

a third conduit means connecting the outlet port of the mixing means to the detector capable of analyzing liquids.

14. The apparatus of claim 13 further comprising a means for heating said first conduit means.

15. The apparatus of claim 13 wherein the means for delivering the flow of liquid solvent comprises a pump.

16. The apparatus of claim 13 further comprising a means for heating the mixing means.

17. The apparatus of claim 12 wherein the chromatography instrument comprises a capillary gas chromatograph.

18. The apparatus of claim 12 further comprising a degassing means located after the means for entraining the effluent and before the detector capable of analyzing liquids.

19. The apparatus of claim 12 wherein the detector capable of analyzing liquids is a liquid radioactivity monitor, and the liquid solvent contains a scintillating material.

20. An interface for coupling an output end of a gas chromatograph to a detector designed for liquid applications, comprising:

a low volume tee having two inlet ports and one outlet port;

a heated transfer means for connecting the output of the gas chromatograph directly to a first inlet port of the low volume tee;

a first conduit means for connecting a second inlet port of the low volume tee to a supply of solvent;

a second conduit means for connecting the output port of the low volume tee to a liquid chromatography detector.

21. The interface of claim 20 further comprising a means for heating the low volume tee.
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