Determination of Compound-Specific Carbon Isotopic Compositions of Trace-Level Volatile Organic Compounds in Aqueous Phases Using SPME-Cryofocus GC-IRMS Technique

Compound-specific carbon isotope ration analysis is a promising tool to assess the origin and fate of organic contaminants, however, the low concentrations of dissolved organic pollutants and the difficulty to concentrate or extract have been the major facts limiting the application of stable isotope tracing techniques at contaminated field sites. In this paper, we developed a method combining SPME with cryofocus technique for the compound-specific carbon isotope analysis of volatile organic compounds in aqueous phase, samples were extracted with SPME and then cryofocus to the front part of GC column, the samples were cumulated after several times of extraction and meet the detection limit. The detection limit using this method was 10 times improved than the conventional SPME method. Under the optimum analytical condition, aqueous samples Trichloroethene, Tetrachloroethene, Benzene and Toluene were analyzed, δ¹³C fractionation compared to pure-phase analysis was less than 0.5×10^-3, the reproducibility was better than ±0.3×10^-3. GC-IRMS coupling with SPME and Cryofocus technique proved to be a promising and accurate method for the determination of carbon isotope composition of trace-level volatile organic compounds in aqueous phases.