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 nitro gen to be determined for individual compounds introduced via a gas chr omatograph. It is the first combustion method that allows direct measu rement of isotope ratios of individual molecular components of mixture s. Unlike traditional gas isotope ratio measurements made on pure samp les, the method requires only very small samples, viz. several picolit res of the vapour. This paper reviews the principles and history of ga s isotope ratio monitoring, focusing on the instrumentation used in is otope ratio monitoring GC/MS, including the combustion procedures used for atomization. Standardization methods and data manipulation techni ques are described, as are applications to geochemistry, biology, medi cine and other areas of science.