title: Development of new method of δ13C measurement for trace hydrocarbons in natural gas using solid phase micro-extraction coupled to gas chromatography isotope ratio mass spectrometry.
abstract: Compound specific isotope analysis (CSIA) of normal-level hydrocarbons (C1-C4) in natural gas is often successfully used in natural gas origin identification and classification, but little progress so far has been made for trace level hydrocarbons (C5-C14) in natural gas. In this study, we developed a method for rapid analysis of carbon isotopic ratios for trace hydrocarbons in natural gas samples. This method can be described as a combined approach characterized by solid phase micro-extraction (SPME) technique coupled to gas chromatography isotope ratio mass spectrometry (GC/IRMS). In this study, the CAR-PDMS fiber was chosen as the SPME adsorptive material after comparative experiments with other four fibers, and the parameters, including equilibration time, extraction temperature and desorption time, for efficient extraction of trace hydrocarbons were systematically optimized. The results showed the carbon isotopic fractionation was not observed as a function of equilibration time and extraction temperature. And the δ13C signatures determined by SPME-GC/IRMS were in good agreement with the known δ13C values of C5-C14measured by GC-IRMS, and the accuracy is generally within ±0.5‰. Five natural gas samples were analyzed using this method, and the δ13C values for C5-C14components were obtained with satisfied repeatability. The SPME-GC/IRMS approach fitted with CAR-PDMS fiber is well suited for the preconcentration of trace hydrocarbons and provides so far the most reliable carbon isotopic analysis for trace compounds in natural gas.
authors.affiliation: Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China; School of Earth Sciences and Gansu Key Laboratory of Mineral Resources in Western China, Lanzhou University, Lanzhou 730000, China. Electronic address: lizhongping@lzb.ac.cn.
authors.forename: Zhongping
authors.initials: Z
authors.lastname: Li
authors.affiliation: Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China.
authors.forename: Xibin
authors.initials: X
authors.lastname: Wang
authors.affiliation: Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China.
authors.forename: Liwu
authors.initials: L
authors.lastname: Li
authors.affiliation: School of Earth Sciences and Gansu Key Laboratory of Mineral Resources in Western China, Lanzhou University, Lanzhou 730000, China.
authors.forename: Mingjie
authors.initials: M
authors.lastname: Zhang
authors.affiliation: College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China.
authors.forename: Mingxin
authors.initials: M
authors.lastname: Tao
authors.affiliation: Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China.
authors.forename: Lantian
authors.initials: L
authors.lastname: Xing
authors.affiliation: Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China.
authors.forename: Chunhui
authors.initials: C
authors.lastname: Cao
authors.affiliation: Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, China.
authors.forename: Yanqing
authors.initials: Y
authors.lastname: Xia
keywords: Carbon isotope; Gas chromatography; Isotope ratio mass spectrometry; Natural gas; Solid-phase micro extraction; Trace hydrocarbons