| abstract |
The invention comprises an on-line mass spectrometric method and apparatus for the determination of the isotopic composition of at least oxygen, hydrogen and nitrogen in a compound or mixture of compounds. A mixture contained in syringe 6 is injected through injector 7 on a chromatographic column 1. Compounds eluting from the column 1 pass into a catalytic reactor 14 (typically a platinum\rhodium capillary tube containing elemental carbon and maintained at 1200°C) and are decomposed to produce carbon monoxide, molecular nitrogen, and molecular hydrogen. These gases are analyzed by an isotope-ratio mass spectrometer 4 so that the isotopic composition of the oxygen, nitrogen and hydrogen comprised in the original compound can be determined. A second chromatographic column 24 may be provided to separate carbon monoxide and nitrogen before they are passed into the spectrometer 4, thereby allowing a low resolution spectrometer to be used for the analysis of both gases at m/e 28 daltons. When only nitrogen is to be determined, the second chromatographic column 24 may be replaced by a methanizer. nAn alternative embodiment for determination of carbon isotopic composition uses a reactor 14 containing an oxygenated compound, e.g. water. |