Preparation of trace amount of atmospheric methane for measuring <sup>14</sup>C isotopic ratio

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  • MORIIZUMI Jun
    Dept. of Nuclear Engineering, School of Engineering, Nagoya University
  • NAGAMINE Koichiro
    Dept. of Nuclear Engineering, School of Engineering, Nagoya University (Present address) Division of Informatics for Natural Science, Graduate School of Human Informatics, Nagoya University
  • IIDA Takao
    Dept. of Nuclear Engineering, School of Engineering, Nagoya University
  • IKEBE Yukimasa
    Dept. of Nuclear Engineering, School of Engineering, Nagoya University
  • NAKAMURA Toshio
    Dating and Materials Research Center, Nagoya University

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Other Title
  • 大気中メタンの<sup>14</sup>C同位体比測定のための試料調製
  • 大気中メタンの14C同位体比測定のための試料調製
  • タイキチュウ メタン ノ 14C ドウイタイヒ ソクテイ ノ タメ ノ シリョ

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Description

Carbon-14 isotopic measurements of atmospheric methane (CH4) provide useful information on its sources and behavior. We have assembled a preparation line to concentrate and purify low levels (〜2 ppmv) of methane for the measurement of 14C content with accelerator mass spectrometry (AMS). In this system, trace amounts of methane in nearly 1 m3 of air sample are cryogenically adsorbed on active carbon, purified by gas chromatography, combusted and collected as carbon dioxide. The mean yield of this procedure is 88.6±5.8 (1σ) %. Carbon dioxide, obtained from the above procedure, is divided into two parts : one portion is converted to graphite for AMS, and the other is used for δ13C measurement. Sample contamination is negligible compared with the precision of 〜1 pM (1σ) for AMS. The effect of isotopic fractionation in this procedure is also smaller than any of the source of contamination. The overall error of this procedure is lower than 1 ‰ for the δ13C measurement. From isotopic measurements of atmospheric methane in Nagoya City at the beginning of 1994, we found a high methane concentration air sample in which 14C content of methane was lower. This implies the contribution of fossil methane to the urban atmosphere.

Journal

  • Chikyukagaku

    Chikyukagaku 29 (2), 99-111, 1995

    The Geochemical Society of Japan

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