High-precision delta H-2 and delta O-18 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 delta(2)H and delta(18)O by continuous-flow isotope ratio mass spectrometry. A pyrolysis furnace packed;vith 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 H2O and CO2. The isotope ratio mass spectrometer used gives adequate separation of (HH+)-H-2-H-1 and He-4(+) to allow use of He as carrier gas. The pyrolysis technique provides a rapid method for analysis of water with a precision of +/-2 parts per thousand for delta(2)H and +/-0.3 parts per thousand for delta(18)O. Similar precisions are obtained for injections of 0.5 mu L of urine and volatile organic compounds. Memory between samples is <2% for both delta(2)H and delta(18)O measurement. The technique is accurate over a wide range of enrichment for both delta(2)H and delta(18)O and is suitable for use in natural abundance and tracer studies of liquid samples.