High Precision Isotope Ratio Monitoring Techniques in Mass Spectrometry

Isotope ratio monitoring following on-line combustion is a new method in gas chromatography/mass spectrometry (GC/MS) that allows the ratios of abundances of stable isotopes of elements such as carbon and nitrogen to be determined for individual compounds introduced via a gas chromatograph. It is the first combustion method that allows direct measurement of isotope ratios of individual molecular components of mixtures. Unlike traditional gas isotope ratio measurements made on pure samples, the method requires only very small samples, viz. several picolitres of the vapour. This paper reviews the principles and history of gas isotope ratio monitoring, focusing on the instrumentation used in isotope ratio monitoring GC/MS, including the combustion procedures used for atomization. Standardization methods and data manipulation techniques are described, as are applications to geochemistry, biology, medicine and other areas of science.