[Identification of photoproducts for PCB congeners by the new retention index system]

Polychlorinated biphenyls (PCBs) are a kind of priority pollutants, constituting a complex group of 209 congeners ranging from monochloro to decachlorobiphenyls. Because of the shortcomings of retention time data and the lack of suitable retention index systems, the congeners analysis of PCBs is one of the most challenging tasks in capillary column gas chromatography (GC), especially due to the fact that the isomers of PCBs can not be identified by GC-MS. A new retention index system, suitable for analysis of PCB congeners in the environmental samples by temperature-programmed capillary gas chromatography with ECD, has been developed recently by Chu et al. In this paper, retention indexes of all 209 PCB congeners were calculated according to the new retention index system from their respective retention times reported by other authors. The photoproducts of PCB87, PCB138 and PCB169 were identified with the new retention index system and confirmed by GC-MS. The deviations of retention indexes for all photoproducts were within 3 index units. It was testified that the above retention index system was reliable during the identification of PCB congeners and would have wide applicability. Based on the formations of coplanar PCB congeners (PCB77 and PCB126) during the photodegradations of PCB138 and PCB169, it was proposed that toxic equivalence (TEQ) should be used as a kind of quality indicator for the studies of the photolysis of PCBs.