New technologies for small sample stable isotope measurement: static vacuum gas source mass spectrometry, laser probes, ion probes and gas chromatography-isotope ratio mass spectrometry

Abstract

Since there are 83 natural elements, any review of the use of mass spectrometry for the study of abundance and isotopic compositions of individual species in a geological environment, including locations beyond the Earth, has of necessity to be selective. This paper will focus on the studies of the so-called “light elements”: hydrogen, carbon, nitrogen, oxygen, silicon and sulphur and their isotope systems. Five of the elements chosen (H, C, O, N and si) are amongst the most abundant in the cosmos, four (H, C, O and N) contribute substantially to life processes and choosing either C or Si together with O would allow as to account for > 60% of virtually all rocks. To further restrict the subject matter, I intend to concentrate on advances in the techniques for measurement of these elements. Amongst the most important advances in technology are the following: (i) the reduction of sample requirements for gas source stable isotope mass spectrometry into the picomole range; (ii) the application of focussed lasers as a means of extracting gas for isotopic measurement; (iii) a demonstration of the abilities of the ion microprobe (SIMS) in producing isotope measurements; and (iv) coupling of gas chromatography to stable isotope mass spectrometers for compound specific isotope analysis of complex mixtures. Some of the scientific highlights which have been achieved by the above means are respectively: (i) the identification of individual silicon carbide minerals as grains of interstellar dust; (ii) the demonstration of growth effects in diamonds of terrestrial and extraterrestrial origin; (iii) mineral specific isotopic compositions for complex geological materials; and (iv) unravelling the origin of mixtures of biomarkers in sedimentary environments.