Abstract:

In China, the detection methods for polychlorinated biphenyls (PCBs) in aquatic products are mainly effective for 6 indicative PCBs and 12 coplanar dioxin-like PCBs, which only account for a limited proportion of PCBs in organisms. In this study, to obtain the detailed concentration levels of PCBs in organisms, elucidate the metabolism and enrichment characteristics of PCBs in organisms, and accurately evaluate the exposure level and risks of PCBs to humans, an improved method for the simultaneous determination of 82 PCBs in fish and shellfish samples was developed using isotope dilution-high resolution gas chromatography-high resolution mass spectrometry (ID-HRGC-HRMS). The recovery and reproducibility of two extraction methods, i. e., oscillatory extraction and accelerated solvent extraction (ASE), were compared. Finally, ASE was chosen for subsequent experiments. Specifically, after adding 1 ng¹³C-labeled extraction internal standards, the samples were extracted under pressure by ASE using a mixture of n-hexane-dichloromethane (1∶1, v/v). The experimental conditions employed for this were a pressure of 10.3 MPa, heating temperature of 100 ℃, heating time of 5 min, static time of 8 min, flush volume of 60%, purging time of 120 s, and 34 mL cells. Subsequently, the extracts were loaded on an 8 g acid silica gel (44%) column (inner diameter: 15 mm) and eluted with 90 mL of n-hexane. After purification and concentration, the analytes were determined by HRGC-HRMS with a fused-silica capillary column (DB-5MS, 60 m×0.25 mm×0.25 μm). The temperature program was optimized to separate the most target compounds at the baseline. Specifically, the initial oven temperature was 120 ℃, which was held for 1 min, following by heating to 180 ℃ at 30 ℃/min, heating to 210 ℃ at 2 ℃/min and holding for 1 min, and further heating to 310 ℃ at 2.5 ℃/min and holding for 1 min. The injector and ion source temperatures were 270 ℃ and 280 ℃, respectively. With a static resolution of 10000, the HRMS instrument was operated in the selected-ion monitoring mode at an electron energy of 35 eV. The 82 PCBs were qualified by their retention time and two characteristic ions, and thereafter quantified using the mean relative corresponding factor (RRF). The results showed that the relative standard deviation (RSD) of the RRF obtained from six-point calibration standard solutions was less than 20%. The linearity ranges were from 0.1 to 200 μg/L, and the correlation coefficients (r²) were greater than 0.99. Under optimum conditions, the method detection limits (MDLs) for the PCBs of biological samples were in the range of 0.02-3 pg/g. To validate the method, the fish and shellfish samples were spiked with a low level (0.4 ng) and high level (3.6 ng) of native PCB standards. The spiked recoveries using low-concentration native PCBs were 71.3%-139% in fish and 76.9%-143% in shellfish, and the RSDs (n=7) were 2.1%-14% and 4.5%-14%, respectively. The spiked recoveries using high-concentration native PCBs were 77.6%-141% and 82.2%-131%, respectively, and the RSDs (n=7) were 1.4%-9.4% and 1.7%-11%, respectively. An analysis of fresh fish and shellfish samples showed that the contents of a single PCB ranged from “not detected” to 54.1 pg/g, where 12 coplanar dioxin-like PCBs were detected in the range of 12.6 pg/g to 74.5 pg/g, six indicative PCBs in the range of 30.9 pg/g to 62.1 pg/g, and 82 PCBs in the range of 174 pg/g to 672 pg/g. It was concluded that this method could be successfully applied for the determination of PCBs in biological samples with good accuracy and precision. This comprehensive analytical method of PCBs in aquatic products provides effective technical support for biological monitoring; it will also aid in ecological and environmental management and the implementation of the Stockholm Convention policies.

Key words: accelerated solvent extraction (ASE), isotope dilution-high resolution gas chromatography-high resolution mass spectrometry (ID-HRGC-HRMS), environmental monitoring, polychlorinated biphenyls (PCBs), fish, shellfish