Gas chromatography/mass spectrometry/isotope ratio mass spectrometry (GC/MS/IRMS) methods for ??13C measurement of the halomethanes CH3Cl, CH3Br, CH3I and methanethiol (CH3SH) during studies of their biological production, biological degradation, and abiotic reactions are presented. Optimisation of gas chromatographic parameters allowed the identification and quantification of CO2, O2, CH3Cl, CH3Br, CH3I and CH3SH from a single sample, and also the concurrent measurement of ??13C for each of the halomethanes and methanethiol. Precision of ??13C measurements for halomethane standards decreased (??0.3, ??0.5 and ??1.3%???) with increasing mass (CH3Cl, CH3Br, CH3I, respectively). Given that carbon isotope effects during biological production, biological degradation and some chemical (abiotic) reactions can be as much as 100???, stable isotope analysis offers a precise method to study the global sources and sinks of these halogenated compounds that are of considerable importance to our understanding of stratospheric ozone destruction. ?? 2001 John Wiley & Sons, Ltd.
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Continuous flow stable isotope methods for study of ??13C fractionation during halomethane production and degradation