Abstract On-line gas chromatography–pyrolysis coupled to gas chromatography–isotope ratio mass spectrometry was used here for the position-specific isotope analysis (PSIA) of propane. First, based on the conversion rate of propane and its products, 800–840 °C was considered optimal for propane pyrolysis. The major pyrolytic fragments of propane included CH4, C2H4, C3H6, and C2H6. Subsequent isotope labeling experiments showed that CH4 and C2H6 were derived entirely from the terminal carbons, whereas C2H4 and C3H6 were derived from both terminal and central positions of propane. Therefore, the 13C enrichment factor associated with the major reactions during the pyrolysis process and position-specific δ13C values of propane can be estimated from the amount and δ13C values of the pyrolytic fragments using isotope mass balance. The obtained enrichment factors depended on the pyrolysis temperature, which can be used to calculate position-specific δ13C values for propane measured with this system. The results suggest that a relatively accurate site-preference value for propane can be obtained by this method. Therefore, the combination of compound-specific isotope analysis and PSIA of propane will be a powerful tool to discriminate the different origins of gases.

中文翻译：

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确定天然气中丙烷的特定位置碳同位素比

摘要 在线气相色谱-热解与气相色谱-同位素比质谱联用在这里用于丙烷的位置特异性同位素分析 (PSIA)。首先，根据丙烷及其产物的转化率，800–840 °C 被认为是丙烷热解的最佳温度。丙烷的主要热解碎片包括 CH4、C2H4、C3H6 和 C2H6。随后的同位素标记实验表明 CH4 和 C2H6 完全来自末端碳，而 C2H4 和 C3H6 来自丙烷的末端和中心位置。因此，与热解过程中的主要反应相关的 13C 富集因子和丙烷的位置特定 δ13C 值可以使用同位素质量平衡从热解碎片的数量和 δ13C 值估计。获得的富集因子取决于热解温度，可用于计算用该系统测量的丙烷的位置特定 δ13C 值。结果表明，通过这种方法可以获得相对准确的丙烷位点偏好值。因此，化合物特定同位素分析和丙烷 PSIA 的结合将成为区分不同气体来源的有力工具。