天然および人工起源メタンの炭素同位体比測定 [in Japanese] Carbon isotope measurement of natural and anthropogenic methane [in Japanese]
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We have collected various kinds of gas samples, which are expected to be source of atmospheric methane. Chemical compositions and δ<sup>13</sup>C values of the gas samples were measured by using a gas chromatograph and a combined gas chromatograph/combustion/isotope ratio mass spectrometer (GC/C/IRMS ) system, respectively. Analytical precision of δ<sup>13</sup>C value measurement by using GC/C/IRMS system was examined. Overall error of measurement is between 1 ‰ and 2 ‰, estimated from repeated analysis of running standard gas and δ<sup>13</sup>C variation with the combustion efficiency. Observed δ<sup>13</sup>C values of the methane vary singificantly from -65.2‰ to -22.9‰, agrees well with data from literatures. Taking into account a positive correlation between <sup>3</sup>He/<sup>4</sup>He ratios and δ<sup>13</sup>C values and a recent trend of atmospheric <sup>3</sup>He/<sup>4</sup>He ratio, we discuss contribution of fossil fuel methane to the increase of atmospheric methane.
Chikyukagaku 26(2), 105-114, 1993
The Geochemical Society of Japan