On-line pyrolysis of hydrocarbons coupled to high-precision carbon isotoperatio analysis

High-precision carbon isotope ratios are reported for gas phase pyrolysis p roducts of toluene and iz-alkanes from C5 to C10. Toluene yields benzene an d methane exclusively, while n-alkanes yield methane and a-olefins. Pyrolys is product isotope ratios were determined with a mean precision of SD(delta (13)C) < 0.2 parts per thousand and were not strongly dependent on pyrolysi s temperature. Carbon yields from benzene and methane appear at the expecte d ratio of 6:1 at 4% fragmentation but drop at fragmentation <20%. Carbon y ields from n-alkanes were not at the expected ratios even at the lowest deg rees of fragmentation, with ethylene at greatest intensity, indicating the presence of secondary reactions. The carbon isotope ratio of methane was de pleted by >15 parts per thousand on average compared to the parent alkanes for all but octane, where it was enriched by almost 1 parts per thousand. C omplementary binary fragment isotope ratios were closely correlated to the isotope ratio of the parent. These data show that high-precision isotope ra tios of hydrocarbon pyrolysis products are indicative of source and will be useful for fingerprinting and on-line position-specific isotope analysis ( PSIA). (C) 1999 Elsevier Science B.V. All rights reserved.