HIGH-PRECISION CONTINUOUS-FLOW ISOTOPE RATIO MASS-SPECTROMETRY

Although high-precision isotope determinations are routine in many are as of natural science, the instrument principles for their measurement s have remained remarkably unchanged for four decades. The introductio n of continuous-flow techniques to isotope ratio mass spectrometry (IR MS) instrumentation has precipitated a rapid expansion in capabilities for high-precision measurement of C, N, O, S, and H isotopes in the 1 990s. Elemental analyzers, based on the flash combustion of solid orga nic samples, are interfaced to IRMS to facilitate routine C and N isot opic analysis of unprocessed samples. Gas/liquid equilibrators have au tomated O and H isotopic analysis of water in untreated aqueous fluids as complex as urine. Automated cryogenic concentrators permit analysi s at pair-pet-million concentrations in environmental samples. Capilla ry gas chromatography interfaced to IRMS via on-line microchemistry fa cilitates compound-specific isotope analysis (CSIA) for purified organ ic analytes of I nmol of C, N, or O. CC-based CSIA for hydrogen and li quid chromatography-based interfaces to IRMS have both been demonstrat ed, and continuing progress promises to bring these advances to routin e use. Automated position-specific isotope analysis (PSIA) using nonca talytic pyrolysis has been shown to produce fragments without apprecia ble carbon scrambling or major isotopic fractionation, and shows great promise for intramolecular isotope ratio analysis. Finally IRMS notat ion and useful elementary isotopic relationships derived from the fund amental mass balance equation are presented. (C) 1998 John Wiley & Son s, Inc.