Use of a temperature‐programmable injector coupled to gas chromatography–combustion–isotope ratio mass spectrometry for compound‐specific carbon isotopic analysis of polycyclic aromatic hydrocarbons

Abstract

Compound-specific isotopic analysis (CSIA) can provide information about the origin of analysed compounds; for instance, polycyclic aromatic hydrocarbons (PAHs) in aerosols. This could be a valuable tool in source apportionment of particulate matter (PM) air pollution. Because gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) analysis requires an amount of at least 10 ng of an individual PAH, a high concentration of PAHs in the injected extract is needed. When the concentration is low a large volume injector creates the possibility of introducing a satisfactory amount of individual PAHs. In this study a temperature-programmable injector was coupled to GC-C-IRMS and injection parameters (solvent level, transfer column flow, transfers time) were optimised using six solid aromatic compounds (anthracene, fluoranthene, pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene) dissolved in n-pentane and EPA 610 reference mixture. CSIA results for solid PAHs were compared with results obtained for the single components analysed by elemental analysis-isotope ratio mass spectrometry. The injection method was validated for two sample injection volumes, 50 and 100 microL. This method was also compared with commonly used splitless injection. To be included in the study, measurements had to have an uncertainty lower than 0.5 per thousand for delta(VPDB)13C and a minimum peak height of 200 mV. The lower concentration limits at which these criteria were fulfilled for PAHs were 30 mg/L for 1 microL in splitless injection and 0.3 and 0.2 mg/L for 50 and 100 microL, respectively, in large volume injection.