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

An on-line pyrolysis technique is described for analysis of δ 2 H and δ 18 O 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 H 2 and CO. A water trap and postpyrolysis gas chromatograph separate analyte gases from traces of H 2 O and CO 2 . The isotope ratio mass spectrometer used gives adequate separation of 2 H 1 H + and 4 He + 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 δ 2 H and ±0.3‰ for δ 18 O. Similar precisions are obtained for injections of 0.5 μL of urine and volatile organic compounds. Memory between samples is <2% for both δ 2 H and δ 18 O measurement. The technique is accurate over a wide range of enrichment for both δ 2 H and δ 18 O and is suitable for use in natural abundance and tracer studies of liquid samples.