Rolling revolution in analytical isotope geochemistry

Abstract

The many subjects of isotope geochem. have two things in common: they generally require anal. of isotope ratios at low natural abundances (∼10^(-2)-10^(-6)) and high precision (∼10^(-3)-10(-6)). For the first 50 years of this field (ca. 1950-2000), these requirements were met by a narrow range of technologies - mostly low mass resoln. (M/ΔM of a few hundred) TIMS and gas source IRMS - that limited the field to a few simple mols. and elements. Over the last 15 years this field has been transformed by the emergence of a wide range of new instruments and methods: plasma-source, high-resoln. MC-ICPMS has dramatically expanded the list of easily analyzed elements, and, a variety of technologies have opened up the world of mol. isotopic structure (site specific effects and multiple substitutions), including: high-precision, natural-abundance NMR; GC-pyrolysis-GCIRMS expts.; IR absorption spectroscopy; and high- sensitivity, high-mass-resoln. gas source IRMS. These technologies generally complement one another rather than competing directly, and are collectively supporting a revolution in the way in which mol. isotopic structure is used to create novel geochem. tools - high- dimensionality forensic fingerprints; highly specific metabolic signatures; thermometers based on intramol. isotopic distributions. The pace of this work has accelerated dramatically in the last ∼5 years, and is likely to expand further in coming years with the introduction of instruments having distinctive capabilities and no prior history of use in this field (e.g., terahertz spectroscopy; Fourier-transform mass spectrometry).