Comparison of methods to determine triple oxygen isotope composition of N ₂O

RATIONALE: The oxygen isotope anomaly, ?17O, of N2O and nitrate is useful to elucidate nitrogen oxide dynamics. A comparison of different methods for ?17O measurement was performed. METHODS: For ?17O measurements, N2O was converted into O2 and N2 using microwave-induced plasma in a quartz or corundum tube reactor, respectively, or conversion was carried out in a gold wire oven. In each case, isotope ratios were measured by isotope ratio mass spectrometry. RESULTS: All the tested methods showed acceptable precision (coefficient of variation<2.4 % at 160 nmol N2O) with high sample size but the sample size dependence was lowest when using microwave-induced plasma in a corundum tube reactor. CONCLUSIONS: The use of microwave-induced plasma in a corundum tube yields best results for ?17O measurement on N2O gas samples.