Gas chromatograph-combustion system and method for mass spectrometry
A gas chromatograph-combustion apparatus and method are disclosed in which the carrier gas type and flow rate is continuously exchanged to facilitate high speed, high sensitivity compound specific isotope analysis. Samples are injected into a gas chromatograph that uses H 2 as the carrier gas. The gas stream exiting the gas chromatograph is passed through a combustion system in which H 2 and the samples are combusted, simultaneously and totally, to oxidize the sample to CO 2 and/or N 2 gas, and to convert H 2 gas to water vapor. Water vapor is removed using a water separator. Therefore, combustion serves the dual purpose of preparing the samples for isotopic analysis and converting H 2 to water vapor, which can be easily separated out. A second carrier gas may be used to convey the CO 2 and N 2 to a mass spectrometer where the isotopic composition (e.g. 14 C or 15 N) is determined.
1. A method for analyzing a sample, comprising:
injecting samples and a hydrogen carrier gas into a gas chromatograph;
separating samples into a plurality of compounds to produce an output gas stream from the gas chromatograph;
mixing the output gas stream from the gas chromatograph with oxygen gas and an inert carrier gas suitable for a mass spectrometer to produce an input gas stream for a combustion system;
combusting, substantially completely, the hydrogen carrier gas in the input gas stream of the combustion system to produce an output gas stream from the combustion system, wherein the output gas stream of the combustion system includes the inert carrier gas, carbon dioxide gas, and water vapor;
substantially removing the water vapor from the output gas stream of the combustion system using a water separator to produce a gas stream for analysis, wherein the gas stream for analysis comprises the inert carrier gas and the carbon dioxide gas; and
providing the gas stream for analysis to the mass spectrometer fitted with a gas ion source.
2. The method in claim 1 , wherein the mass spectrometer includes at least one of an isotope ratio mass spectrometer and an accelerator mass spectrometer.
3. The method in claim 1 , wherein mixing the output gas stream from the gas chromatograph with oxygen gas comprises:
providing an amount of oxygen gas at substantially the stoiciometric ratio of 2:1 with the hydrogen carrier gas to allow for combustion to occur substantially completely.
4. The method in claim 1 , wherein combusting at least one of the hydrogen carrier gas and the sample in the input gas stream of the combustion system comprises using metal and metal oxides as a catalyst.
5. The method in claim 1 , wherein the output gas stream of the combustion system further includes nitrogen gas, and the gas stream for analysis further includes nitrogen gas.
6. The method in claim 5 , wherein the output gas stream of the combustion system further includes oxides of nitrogen, and the gas stream for analysis further includes oxides of nitrogen.
7. The method in claim 5 , further comprises:
substantially removing nitrogen oxide in the gas stream for analysis in a reduction furnace to reduce nitrogen oxide into nitrogen gas.
8. The method in claim 1 , wherein the inert carrier gas is helium gas or argon gas.
9. The method of claim 1 , wherein separating samples into a plurality of compounds includes separating into a one or more components, each component having one or more compounds.
10. A method for analyzing a sample, comprising:
injecting samples, an inert carrier gas, and a hydrogen carrier gas into a gas chromatograph, wherein the inert carrier gas is suitable for a mass spectrometer fitted with a gas ion source;
separating samples into a plurality of compounds to produce an output gas stream from the gas chromatograph;
mixing the output gas stream from the gas chromatograph with oxygen gas to produce an input gas stream for a combustion system;
combusting, substantially completely, the hydrogen carrier gas in the input gas stream of the combustion system to produce an output gas stream from the combustion system, wherein the output gas stream from the combustion system includes the inert carrier gas, carbon dioxide gas, and water vapor;
substantially removing the water vapor from the output gas stream of the combustion system using a water separator to produce a gas stream for analysis, wherein the gas stream for analysis comprises the inert carrier gas and the carbon dioxide gas; and
providing the gas stream for analysis to the mass spectrometer fitted with the gas ion source.
11. The method of claim 10 , wherein separating samples into a plurality of compounds includes separating into a one or more components, each component having one or more compounds.
12. A method for interfacing a gas chromatograph with a mass spectrometer, comprising:
injecting samples and a hydrogen carrier gas into a gas chromatograph, wherein the hydrogen carrier gas has a flow rate suitable for gas chromatography;
separating samples into a plurality of compounds using the gas chromatograph to produce a first gas stream;
mixing the first gas stream with oxygen gas and an inert carrier gas to form a second gas stream, wherein the inert carrier gas has a flow rate suitable for mass spectrometry;
combusting the hydrogen carrier gas in the second gas stream substantially completely to produce a third gas stream, wherein combusting the second gas stream removes the hydrogen carrier gas while the inert carrier gas remains, and wherein the third gas stream comprises the inert carrier gas and combustion products;
substantially removing water vapor from the third gas stream to form a fourth gas stream; and
providing the fourth gas stream to a gas ion source fitted to the mass spectrometer.
13. The method in claim 12 , wherein the flow rate suitable for gas chromatography is about 1 to about 100 milliliters per minute.
14. The method in claim 12 , wherein the flow rate suitable for mass spectrometry is about 0.001 to about 1.0 milliliters per minute.
15. The method in claim 12 , wherein the gas ion source is at least one of a microwave plasma ion source and an electron ionization source.
16. The method of claim 12 , wherein separating samples into a plurality of compounds includes separating into one or more components, each component having one or more compounds.