On-line pyrolysis of hydrocarbons coupled to high-precision carbon isotope ratio analysis Original Research Article

High-precision carbon isotope ratios are reported for gas phase pyrolysis products of toluene and n-alkanes from C5 to C10. Toluene yields benzene and methane exclusively, while n-alkanes yield methane and α-olefins. Pyrolysis product isotope ratios were determined with a mean precision of SD(δ13C) < 0.2‰ and were not strongly dependent on pyrolysis temperature. Carbon yields from benzene and methane appear at the expected ratio of 6:1 at 4‰ fragmentation but drop at fragmentation <20%. Carbon yields from n-alkanes were not at the expected ratios even at the lowest degrees of fragmentation, with ethylene at greatest intensity, indicating the presence of secondary reactions. The carbon isotope ratio of methane was depleted by >15‰ on average compared to the parent alkanes for all but octane, where it was enriched by almost 1‰. Complementary binary fragment isotope ratios were closely correlated to the isotope ratio of the parent. These data show that high-precision isotope ratios of hydrocarbon pyrolysis products are indicative of source and will be useful for fingerprinting and on-line position-specific isotope analysis (PSIA).