title: Development of an advanced on-line position-specific stable carbon isotope system and application to methyl tert-butyl ether.
abstract: We present an advanced system for on-line position-specific carbon isotope analysis. The main limitation of on-line intramolecular isotope ratio measurements has been that optimal pyrolytic fragments are obtained mostly at temperatures where the analyte has not completely reacted. As a result of undetermined isotopic fractionation, the isotopic signatures of the pyrolysis products are not strictly equal to these of the equivalent moieties in the parent molecule. We designed a pyrolytic unit in which both temperature and reaction time are variable parameters, enabling determination of the enrichment factor of the pyrolysis at optimal temperature by construction of a Rayleigh plot. In the case of methyl tert-butyl ether (MTBE) presented here, a 'pre-pyrolysis' fractionation of MTBE leading to a depletion of 0.9 per thousand was discovered and the enrichment factor of the optimal pyrolysis reaction was determined at -1.7 per thousand. Absolute delta(13)C values of two functional groups of MTBE - the methoxy group and the 2-methylpropane group - could be determined with 95% confidence intervals of 0.4 per thousand and 0.5 per thousand, respectively.
authors.affiliation: Department of Civil Engineering, University of Strathclyde, John Anderson Building, Glasgow G4 0NG, UK. caroline.gauchotte@strath.ac.uk
authors.forename: Caroline
authors.initials: C
authors.lastname: Gauchotte
authors.forename: Gwen
authors.initials: G
authors.lastname: O'Sullivan
authors.forename: Simon
authors.initials: S
authors.lastname: Davis
authors.forename: Robert M
authors.initials: RM
authors.lastname: Kalin