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.