Abstract:

An improved method based on the isotope dilution technique was developed for the determination of 20 polychlorinated biphenyls (PCBs) in fish samples, including seven indicator polychlorinated biphenyls. The analysis was performed by gas chromatography-triple-quadrupole mass spectrometry (GC-MS/MS) in the multiple reaction monitoring (MRM) mode. Two MRM transitions were monitored for each PCB congener for quantitation and qualification purposes. The edible parts of the fish samples were shattered, frozen, and dried. ¹³C-PCB surrogate standards were spiked into the fish samples. The PCBs in fish samples and the surrogate standards were extracted by auto-Soxhlet extraction. The extract was cleaned-up by a disposable multi-layer column packed with acidic silica gel and basic alumina. ¹³C-PCB recovery standards were spiked into the extract before injection. The separation was performed on a TG-5MS capillary column. Quantitation was performed by the internal standard method. Every group of PCBs used a same number chlorinated ¹³C-isotope PCBs congener as the internal standard. The calibration curves of 20 PCB congeners were linear (correlation coefficient (r)>0.99) within the range of 0.05-10 μg/L. For the recovery test, three levels were spiked in matrices. The average recoveries obtained by this method were 80.3%-117.6% and the relative standard deviations (RSDs, n=6) were 5.09%-18.5%. The limits of determination (LODs) were 0.01-0.02 μg/kg. Contents of the 20 PCBs in the fish samples were in the range 1.2-8.8 μg/kg (wet weight), while those of the seven indicator PCBs were in the range 0.68-6.4 μg/kg (wet weight). The method is suitable for determining polychlorinated biphenyls in fish samples.

Key words: fish samples, gas chromatography-triple-quadrupole mass spectrometry(GC-MS/MS), isotope internal standards, polychlorinated biphenyls(PCBs)