delta C-13 and delta H-2 measurement of methane from ecological and geological sources by gas chromatography/combustion/pyrolysis isotope-ratio mass spectrometry

作者：Yarnes Chris^*

来源：Rapid Communications in Mass Spectrometry, 2013, 27(9): 1036-1044.

DOI：10.1002/rcm.6549

RATIONALE The carbon and hydrogen isotopes of methane are useful in differentiating biological (e.g. wetlands, ruminants, biomass burning) and geological methane sources (e.g. fossil fuels, gas hydrates), as well as quantifying pathways of methanotrophism. Continuous-flow isotopic measurements of methane present a set of analytical challenges, including sample size restrictions and separation of CH4 from atmosphere, hydrocarbons, and CO2. METHODS Small-scale modifications were made to a commercial trace-gas preconcentration and sampling unit (Thermo Scientific PreCon-GasBench) for improved isotopic analysis of methane (13C/2H) across a range of gas concentrations. RESULTS The long-term reproducibility of 13C-CH4 values is less than +/- 0.2 parts per thousand (1 sigma). The limit-of-quantitation of 13C-CH4 values is less than 0.8nmol, conveniently measurable within standard gas sampling vials. A reproducibility of better than +/- 4 parts per thousand (1 sigma) is regularly achieved for 2H values from sample sizes greater than 2nmol. The range of measurement, for both 13C and 2H values, is easily extended from ambient concentration (similar to 1.7ppm-v) for preconcentrated samples to percent methane concentrations under subsampling. CONCLUSIONS The automated measurement of 13C-CH4 and 2H-CH4 values, from ambient to percentage concentrations, is possible with minimal modifications to a commercial preconcentration/gas chromatography inlet. Sample matrix interferences (CO2, CnHy, air) are eliminated and simultaneous isotopic measurements of methane and CO2 and/or C1-C4 light hydrocarbons are possible, while still retaining functionality for isotopic measurements of other gas species (e.g. CO2, N2, O2).

• 出版日期2013-5-15