Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences; Key Laboratory of Petroleum Resources, Gansu Province, Lanzhou, China.
College of Safety Science and Engineering, Xi'an University of Science and Technology, Xi'an, China.
Rapid Commun Mass Spectrom. 2023 May 15;37(9):e9494. doi: 10.1002/rcm.9494.
Position-specific (PS) δ C values of propane have proven their ability to provide valuable information on the evolution history of natural gases. Two major approaches to measure PS δ C values of propane are isotopic C nuclear magnetic resonance (NMR) and gas chromatography-pyrolysis-gas chromatography-isotope ratio mass spectrometry (GC-Py-GC-IRMS). Measurement accuracy of the isotopic C NMR has been verified, but the requirements of large sample size and long experimental time limit its applications. GC-Py-GC-IRMS is a more versatile method with a small sample size, but its accuracy has not been demonstrated.
We measured the PS δ C values of propane from nine natural gases using both C NMR and GC-Py-GC-IRMS, then evaluated the accuracy of the GC-Py-GC-IRMS method.
The results show that large carbon isotope fractionations occurred for both terminal and central carbons within propane during pyrolysis. The isotope fractionations during the pyrolysis are reproducible at optimum conditions, but vary between the two GC-Py-GC-IRMS systems tested, affected by experimental conditions (e.g., pyrolysis temperature, flow rate, and reactor conditions).
It is necessary to evaluate and calibrate each GC-Py-GC-IRMS system using propane gases with accurately determined PS δ C values. This study also highlights a need for PS isotope standards for propane and other molecules (e.g., butane and acetic acid).
丙烷的位置特异性 (PS) δ¹³C 值已被证明能够提供有关天然气演化历史的有价值信息。测量丙烷 PS δ¹³C 值有两种主要方法，即同位素质谱法和气相色谱-热解-气相色谱-同位素比质谱法 (GC-Py-GC-IRMS)。同位素质谱法的测量精度已得到验证，但对大样品量和长实验时间的要求限制了其应用。GC-Py-GC-IRMS 是一种更通用的方法，具有较小的样品量，但准确性尚未得到证明。
我们使用 C 核磁共振和 GC-Py-GC-IRMS 测量了来自九种天然气的丙烷 PS δ¹³C 值，然后评估了 GC-Py-GC-IRMS 方法的准确性。
结果表明，在热解过程中，丙烷的末端和中心碳原子都发生了较大的碳同位素分馏。在最佳条件下，热解过程中的同位素分馏是可重复的，但在两个测试的 GC-Py-GC-IRMS 系统之间存在差异，受实验条件（例如热解温度、流速和反应条件）的影响。
有必要使用具有准确测定的 PS δ¹³C 值的丙烷气体来评估和校准每个 GC-Py-GC-IRMS 系统。这项研究还强调了需要为丙烷和其他分子（例如丁烷和乙酸）提供 PS 同位素标准。
