HYDROGEN-ISOTOPE ANALYSIS OF NANOMOLE (PICOLITER) QUANTITIES OF H2O

Abstract

We describe a technique for on-line reduction of water vapor carried in a He stream followed by continuous-flow mass spectrometry of evolved H2 gas. This technique is appropriate for analysis of D/H ratios of ~10-9 to ~5 x 10-8 moles of water and has an external precision (1σ) typically varying between +/-1.0 and 2.0%%. For specific ranges in sample size, temperature of the reduction reaction, and method of introducing evolved vapor into the mass spectrometer, this technique involves negligible analytical corrections (~0 to 3%%) beyond those inherent to gas-source mass spectrometry of molecular hydrogen. We present an analysis of the D/H ratio of water released by stepped heating of a 10-mg fragment of the Shergottite-Nahklite-Chassignite meteorite ALH84001 and ~1 to 2 μg of a terrestrial hydrous mineral (thermonatrite) as examples of possible applications making use of this technique.