High-Precision δ2H and δ18O Measurement for Water and Volatile Organic Compounds by Continuous-Flow Pyrolysis Isotope Ratio Mass Spectrometry

Abstract

An on-line pyrolysis technique is described for analysis of δ2H and δ18O by continuous-flow isotope ratio mass spectrometry. A pyrolysis furnace packed with nickel, on which carbon is deposited as required, is shown to give efficient conversion of nanomole quantities of sample material to H2 and CO. A water trap and postpyrolysis gas chromatograph separate analyte gases from traces of H2O and CO2. The isotope ratio mass spectrometer used gives adequate separation of 2H1H+ and 4He+ to allow use of He as carrier gas. The pyrolysis technique provides a rapid method for analysis of water with a precision of ±2‰ for δ2H and ±0.3‰ for δ18O. Similar precisions are obtained for injections of 0.5 μL of urine and volatile organic compounds. Memory between samples is <2% for both δ2H and δ18O measurement. The technique is accurate over a wide range of enrichment for both δ2H and δ18O and is suitable for use in natural abundance and tracer studies of liquid samples.