Hydrogen-isotope analysis of nanomole (picoliter) quantities of H2O

We describe a technique for on-line reduction of water vapor carried in a He stream followed by continuous-flow mass spectrometry of evolved H-2 gas. This technique is appropriate for analysis of D/H ratios of similar to 10(-9) to similar to5 x 10(-8) moles of water and has an external precision (1 sigma) typically varying between +/-1.0 and 2.0 parts per thousand. 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 (similar to0 to 3 parts per thousand) 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 similar to1 to 2 mug of a terrestrial hydrous mineral (thermonatrite) as examples of possible applications making use of this technique. Copyright (C) 2001 Elsevier Science Ltd.