Two methods of sample preparation for analysis of non-ortho and mono-ortho PCB congeners in the muscles of selected fish species
Background. Polychlorinated biphenyls (PCBs) are persistent organic pollutants widespread in the environment. Their ability to accumulate in living organisms leads to food contamination, which is the main route of human exposure to PCBs. During analytical procedure of PCB residue determination, losses of these compounds may occur, which contribute to obtaining underestimated analytical results. Adequate analytical method of chlorobiphenyls determination should be applied to avoid the losses and obtain high recoveries and furthermore to enable accurate estimation of the risk of consuming contaminated food. Especially fish, due to the high bioaccumulation, may contain considerable amounts of these compounds. The aim of this study was to determine if the method of sample preparation influences the recovery of non-ortho (PCB 77, 81, 126, 169) and mono-ortho (PCB 105, 114, 156, 157) PCB congeners in selected fish species. Materials and Methods. To prepare samples for chromatographic determination (HP 6890/5973 GC MS) two methods were applied. Fish muscle tissues were dried by rubbing in a mortar with anhydrous sodium sulphate or freeze dried (lyophilised) (LyoLAB 3000). The samples were fortified with a known amount of internal standard (decachlorobiphenyl), and some were additionally fortified with the standard solution of analysed PCB congeners. Results. nternal standard recoveries ranged from 57.61 ± 1.21% to 88.76 ± 4.03% in freeze-dried samples, and from 63.81 ± 5.11% to 97.50 ± 6.14% in samples rubbed with anhydrous sodium sulphate. Following lyophilisation, recoveries of analysed PCB congeners varied from 68.88 ± 11.74% for PCB 157 to 79.18 ± 12.33% for PCB 114. In the samples rubbed with anhydrous sodium sulphate the lowest recovery was determined for PCB 77 (72.40 ± 12.34%), the highest being typical for PCB 156 (83.47 ± 12.86%). Following lyophilisation, toxic equivalents (TEQs) for the examined fish species ranged from 0.0050 ng-TEQ·g-1 dry weight in salmon to 0.0299 ng-TEQ·g-1 dry weight in mackerel. Following rubbing with anhydrous sodium sulphate the highest toxic equivalent (0.0326 ng-TEQ·g-1 dry weight) was calculated for mackerel, and the lowest for salmon (0.0055 ng-TEQ·g-1 dry weight). Conclusion. The research has demonstrated that in most cases the results obtained with both methods have not differed significantly (P < 0.05), although freeze drying resulted in slightly higher losses of PCB congeners. Despite of smaller recoveries, freeze drying can be applied because of solvent saving and easier sample preparation.
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