A technique for the determination of 18O/16O and 17O/16O isotopic ratios in water from small liquid and solid samples.

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 δ18O 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 δ18O ± 0.54, δ17O ± 0.33, and Δ17O ± 0.10‰, 1σ in all cases. The technique was developed primarily for ...