Abstract

In this work, problems that may occur during determination of trace levels of polychlorinated biphenyls in sediment samples are described. Main error sources are connected with extraction of analytes prior to final determination. During model studies, polychlorinated biphenyls have been extracted from sedimentreference material (METRANAL 2) with the use of different solvents (dichloromethane, hexsane, and toluene); the process has been enhanced by mechanical shaking or ultrasounds.Seven selected PCBs (PCB 28, 52, 101, 118, 138, 153, and 180 - according to IUPAC) were determined in extracts samples by GC-MS technique. During the studies, two calculation methods were applied to determine the amount of analytes introduced to the chromatographic column. The first approach assumes that the recovery of PCBs that contained a small amount of chlorine atoms in the molecule is similarto the recovery of 13C12PCB28 standard, whereas compounds with greater number ofchlorine atoms in the molecule will be recovered from the sediment similarly to the recoveryof 13C12PCB180 standard. The second approach assumes that the recovery of PCB 138 and PCB 153 is similar to the average value of 13C12PCB28 and 13C12PCB180 standards. In the case of shaking assisted extraction, 55-90% PCB recoveries were achievedwhen toluene was used as a solvent, while 71-86% recovery was achieved when dichloromethane was used. When hexsane was used as solvent, recovery ranged 43-107%. In the case of ultrasounds assisted extraction, PCB recoveries of 50-108% were achieved when toluenewas used as solvent, while 44-101% recovery was achieved when dichloromethane was applied. When hexsane was used as solvent, recovery reached 57-95%. Studies have also shown that, when applying different isolation techniques and different solvents, the recovery of applied 13C12PCB28 and 13C12PCB180 standards is different.Recovery of 13C12PCB28 standard was from 5% (for hexane tenfold extraction assisted by shaking) to 57% (for toluene tenfold extraction assisted by shaking). However, recovery of 13C12PCB180 standard was from 9% (for hexane tenfold extraction assisted by shaking) to 82% (for toluene tenfold extraction assisted by shaking). This is due to the differences of their binding to the sludge matrix. Standard with a greater number of chlorine atoms in the molecule (13C12PCB180) is more weakly associated with sediment than 13C12PCB28 standard. In order to improve the accuracy of the results obtained, it is necessary to use labeled PCB compounds.

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