Publisher： John Wiley & Sons Inc
E-ISSN： 2156-2202|100|D1|1317-1326
ISSN： 0148-0227
Source： Journal Of Geophysical Research, Vol.100, Iss.D1, 1995-01, pp. : 1317-1326
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Abstract
Less than 15 min are required for the determination of δ13CPDB with a precision of 0.2‰ (1σ, single measurement) in 5‐mL samples of air containing CH4 at natural levels (1.7 ppm). An analytical system including a sample‐introduction unit incorporating a preparative gas chromatograph (GC) column for separation of CH4 from N2, O2, and Ar is described. The 15‐min procedure includes time for operation of that system, high‐resolution chromatographic separation of the CH4, on‐line combustion and purification of the products, and isotopic calibration. Analyses of standards demonstrate that systematic errors are absent and that there is no dependence of observed values of δ on sample size. For samples containing 100 ppm or more CH4, preconcentration is not required and the analysis time is less than 5 min. The system utilizes a commercially available, high‐sensitivity isotope‐ratio mass spectrometer. For optimal conditions of sample handling and combustion, performance of the system is within a factor of 2 of the shot‐noise limit. The potential exists therefore for analysis of samples as small as 15 pmol CH4 with a standard deviation of <1‰.
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