A technique for the determination of ¹⁸0/¹⁶0 and ¹⁷0/¹⁶0 isotopic ratios in water from small liquid and solid samples

Baker, L.; Franchi, I.A.; Maynard, J.; Wright, I.P. and Pillinger, C.T. (2002). A technique for the determination of ¹⁸0/¹⁶0 and ¹⁷0/¹⁶0 isotopic ratios in water from small liquid and solid samples. Analytical Chemistry, 74(7) pp. 1665–1673.

DOI: https://doi.org/10.1021/ac010509s

Abstract

We have developed a new technique in which a solid reagent, cobalt(III) fluoride, is used to prepare oxygen gas for isotope ratio measurement from water derived either from direct injection or from the pyrolysis of solid samples. The technique uses continuous flow, isotope ratio monitoring, gas chromatography/mass spectrometry (irmGC/MS) to measure the δ¹⁸0 and δ¹⁷O of the oxygen gas. Water from appropriate samples is evolved by a procedure of stepped pyrolysis (0-1000 °C, typically in 50 °C increments) under a flowing stream of helium carrier gas. The method has considerable advantages over others used for water analysis in that it is quick; requires only small samples, typically 1-50 mg of whole rock samples (corresponding to ~0.2 μmol of H₂O); and the reagent is easy and safe to handle. Reproducibility in isotope ratio measurement obtained from pyrolysis of samples of a terrestrial solid standard are δ¹⁸0 ± 0.54, δ¹⁷0 ± 0.33, and Δ¹⁷0 ± 0.10‰, 1 in all cases. The technique was developed primarily for the analysis of meteorites, and the efficiency of the method is illustrated herein by results from water standards, solid reference materials, and a sample of the Murchison CM2 meteorite.

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