Gas Source Isotope Ratio Mass Spectrometry for the Analysis of Noble Gases

Abstract

Geological processes result in redistribution of noble gases on Earth, with some isotopes being accumulated due to radioactive decay and cosmic irradiation. Therefore noble gas isotope and concentration ratios can be used as tracers of geological processes and geologic age. Analytical techniques for measuring noble gases are complex and differ substantially from the techniques used for stable isotopes. This chapter describes the historical development of noble gas isotope ratio mass spectrometry, sampling requirements, noble gas extraction techniques and sample gas purification and also gives the overview of modern commercially available instruments. Next the referencing strategy and calibration approaches are considered. The only international reference for noble gas isotope ratios is the Earth atmosphere reservoir – an artifact-based scale. In contrast to stable isotopes, noble gas applications require not only relative determinations vs. the international scale but mostly numerical values of isotope and elemental ratios. Up to date many publications refer to the noble gas isotope ratios determined in 1940s. Since then several re-determinations have been reported, being mostly based on commercially available noble gases. Unsolved discrepancies in the isotope ratios, e.g. for atmospheric Ar imply not well-identified uncertainty component for noble gas data which needs more attention. Finally an overview of applications is given.