Abstract:With PreCon-Gas Chromatography/Combustion-Isotope Ratio Mass Spectrometer (PreCon-GC/C-IRMS) combination system, a determination method of stability carbon isotope composition of methane in atmosphere was established about sample and concentration and on-line mass spectrometer analysis. Experiment conditions of the method, stability and linearity of the system, accuracy and precision of the results were analyzed and discussed for measurement of carbon isotope ratio of methane in atmosphere via PreCon-GC/C-IRMS combined technique. Under the current conditions, the system had well linearity (slope＝0.04 ‰/V) when the ion intensity ranged from 1.0 V to 20 V, and it (S=0.03 ‰/V) excelled the total linearity when the ion intensity was from 4.0 V to 15 V. The standard deviation and the maximum deviation were less than 0.3‰ and 0.5‰ respectively, and the recovery reached 99.99%. It demonstrated that the system stability was credible with the accuracy and precision satisfied the analysis requirements. Its application to isotopic characterization, and hence methane source identification, was demonstrated by examination of atmosphere sample collected in indoor and outdoor lawn field. The average δ13C value of methane in indoor atmospheric sample was -31.358‰, and that in outdoor sample was -33.085‰. Furthermore, δ13C value of the methane in atmosphere at the same site varied less than 0.5‰ both during a day and different dates. The results obtained in duplicate revealed the method was reproducible.