Determination of semi-volatile organochlorine compounds in the atmosphere of Singapore using accelerated solvent extraction

Accelerated solvent extraction (ASE) has been applied to the quantitative extraction of organochlorine compounds (OCs), including organochlorine pesticides (HCHs, DDXs) and polychlorinated biphenyls (PCBs) present in both atmospheric particulate and gaseous phase. Extraction parameters such as the combination of solvents, extraction temperature, and static extraction time were investigated and optimized. Effective extraction can be carried out using a 3:1 mixture of n-hexane and acetone as extraction solvents at 100 °C in 20 min for all the compounds studied. The entire analytical procedure developed in this study proves to be reliable as evident from the analysis of specific surrogate standards with the mean recoveries per sample being greater than 82%. The optimized method was validated using NIST-certified SRM 1649a. Semi-volatile OCs, in the atmosphere of Singapore were quantified using the optimized ASE method together with GC-MS. Total average concentrations of ΣHCHs, ΣDDXs, and ΣPCBs in air samples were 244.9 ± 88.5 pg m^-3, 7.7 ± 4.1 pg m^-3, and 34.1 ± 19.7 pg m^-3, respectively. The distribution of these compounds between the gas and particulate phase is discussed. Possible sources of atmospheric OCs are evaluated based on the molecular ratio of specific compounds and backward air trajectory analysis.