Microwave-assisted extraction or saponification combined with microwave-assisted decomposition applied in pretreatment of soil or mussel samples for the determination of polychlorinated biphenyls Original Research Article

Three microwave-assisted techniques (MAT), namely microwave-assisted extraction (MAE), microwave-assisted saponification (MAS) and microwave-assisted decomposition (MAD), were studied and combined to be used in the samples pretreatment to determine polychlorinated biphenyls (PCBs) in soil, sediment and mussels. MAE was employed for the isolation of PCBs, MAS for the saponification of a mussel matrix, and MAD for the elimination of some organochlorine pesticides (OCPs) such as hexachlorocyclohexane (BHC) and DDT, which usually coexisted with PCBs in environmental samples. It was found that acetone-n-hexane (1:1, v/v), methanol and methanolic 1 M KOH solution were all good extractants for MAE of PCBs (recovery >83%), and 15 g mussel could be completely saponified with 30 ml of methanolic 1 M KOH or ethanolic KOH solution by 2 min microwave heating at 100% power output of 600 W. Moreover, 30 ml methanolic 1 M KOH or ethanolic 1 M KOH solution and 2 min microwave heating brought about a complete decomposition for each of 2∼4 μg α-BHC, β-BHC, γ-BHC, δ-BHC, o-p-DDT, p-p-DDT and p-p-DDD, while p-p-DDE, aldrin and dieldrin could only be partly degraded. Furthermore, compared with that by MAD in methanolic 1 M KOH solution, the degradation products of OCPs by MAD in methanolic 1 M KOH solution yielded more peaks in the chromatogram obtained by gas chromatography equipped with electron capture detector (GC-ECD), which may interfere with the GC-ECD detection of PCBs. Therefore, methanolic 1 M KOH solution was chosen as the extractant for the pretreatment of soil or sediment. As a result, the MAD of OCPs could occur along with the MAE of PCBs. Similarly, the MAD of OCPs could well coincide with the MAS of mussels when methanolic 1 M KOH solution was employed as the saponifier for the pretreatment of mussels. Thus, isolating the analytical targets and eliminating the coexisting interferents could be simultaneously carried out using the combined MAT.