Solvent-based dissolution method to sample gas-phase volatile organic compounds for compound-specific isotope analysis

An investigation was carried out to develop a simple and efficient method to collect vapour samples for compound specific isotope analysis (CSIA) by bubbling vapours through an organic solvent (methanol or ethanol). The compounds tested were benzene and trichloroethylene (TCE). The dissolution efficiency was tested for different air volume injections, using flow rates ranging from 25 ml/min to 150 ml/min and injection periods varying between 10 and 40 min. Based on the results, complete mass recovery for benzene and TCE in both solvents was observed for the flow rates of 25 and 50 ml/min. However, small mass loss was observed at increased flow rate. At 150 ml/min, recovery was on average 80 ± 17% for benzene and 84 ± 10% for TCE, respectively in methanol and ethanol. The δ13C data measured for benzene and TCE dissolved in both solvents were reproducible and were stable independently of the volume of air injected (up to 6 L) or the flow rate used. The stability of δ13C values hence underlines no isotopic fractionation due to compound–solvent interaction or mass loss. The development of a novel and simple field sampling technique undertaken in this study will facilitate the application of CSIA to diverse gas-phase volatile organic compound studies, such as atmospheric emissions, soil gas or vapour intrusion.