title: High-temperature reversed-phase liquid chromatography coupled to isotope ratio mass spectrometry.
abstract: Compound-specific isotope analysis (CSIA) by liquid chromatography coupled to isotope ratio mass spectrometry (LC/IRMS) has until now been based on ion-exchange separation. In this work, high-temperature reversed-phase liquid chromatography was coupled to, and for the first time carefully evaluated for, isotope ratio mass spectrometry (HT-LC/IRMS) with four different stationary phases. Under isothermal and temperature gradient conditions, the column bleed of XBridge C(18) (up to 180 °C), Acquity C(18) (up to 200 °C), Triart C(18) (up to 150 °C), and Zirchrom PBD (up to 150 °C) had no influence on the precision and accuracy of δ(13) C measurements, demonstrating the suitability of these columns for HT-LC/IRMS analysis. Increasing the temperature during the LC/IRMS analysis of caffeine on two C(18) columns was observed to result in shortened analysis time. The detection limit of HT-RPLC/IRMS obtained for caffeine was 30 mg L(-1) (corresponding to 12.4 nmol carbon on-column). Temperature-programmed LC/IRMS (i) accomplished complete separation of a mixture of caffeine derivatives and a mixture of phenols and (ii) did not affect the precision and accuracy of δ(13)C measurements compared with flow injection analysis without a column. With temperature-programmed LC/IRMS, some compounds that coelute at room temperature could be baseline resolved and analyzed for their individual δ(13)C values, leading to an important extension of the application range of CSIA.
authors.affiliation: Instrumental Analytical Chemistry, University of Duisburg-Essen, Essen, Germany.
authors.forename: Lijun
authors.initials: L
authors.lastname: Zhang
authors.forename: Dorothea M
authors.initials: DM
authors.lastname: Kujawinski
authors.forename: Maik A
authors.initials: MA
authors.lastname: Jochmann
authors.forename: Torsten C
authors.initials: TC
authors.lastname: Schmidt
mesh_terms: D002110:Caffeine / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry; D002247:Carbon Isotopes / Q000737:chemistry*; D056148:Chromatography, Reverse-Phase / Q000295:instrumentation / Q000379:methods*; D004867:Equipment Design; D006358:Hot Temperature; D016014:Linear Models; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D008956:Models, Chemical; D010636:Phenols / Q000737:chemistry; D012680:Sensitivity and Specificity
chemical_list: D002247:Carbon Isotopes; D010636:Phenols; D002245:Carbon Dioxide; D002110:Caffeine