Measurement of position-specific 13C isotopic composition of propane at the nanomole level. (15th March 2016)

• Record Type: Journal Article
• Authors: Gilbert, Alexis; Yamada, Keita; Suda, Konomi; Ueno, Yuichiro; Yoshida, Naohiro
• Is Part Of: Geochimica et cosmochimica acta. Volume 177(2016:Mar. 15)
• Page Start: 205
• Page End: 216
• Publication Date: 2016-03-15
• Subjects: Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2016.01.017
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: We have developed a novel method for analyzing intramolecular carbon isotopic distribution of propane as a potential new tracer of its origin. The method is based on on-line pyrolysis of propane followed by analysis of carbon isotope ratios of the pyrolytic products methane, ethylene and ethane. Using propane samples spiked with 13 C at the terminal methyl carbon, we characterize the origin of the pyrolytic fragments. We show that the exchange between C-atoms during the pyrolytic process is negligible, and thus that relative intramolecular isotope composition can be calculated. Preliminary data from 3 samples show that site-preference (SP) values, defined as the difference of δ 13 C values between terminal and sub-terminal C-atom positions of propane, range from −1.8‰ to −12.9‰. In addition, SP value obtained using our method for a thermogenic natural gas sample is consistent with that expected from theoretical models of thermal cracking, suggesting that the isotope fractionation associated with propane pyrolysis is negligible. The method will provide novel insights into the characterization of the origin of propane and will help better understand the biogeochemistry of natural gas deposits.