Development of a methodology for the determination of polychlorinated biphenyls in soil samples

The article presents issues related to the development of the chromatographic methodology for determining polychlorinated biphenyls in soil samples. For this purpose, a gas chromatograph equipped with an electron capture detector (GC-ECD) from Perkin Elmer was used. As part of the research, optimal chromatograph parameters were determined, such as injector temperature, ECD detector temperature, oven temperature course during chromatographic analysis, time of analysis and a chromatographic column allowing selective separation of analytes. Then, the chromatographic system was calibrated and the analytical method for polychlorinated biphenyls determination was validated, based on the Supelco and Sigma-Aldrich reference solutions with numbers 47330-U and 36989, respectively. Calibration curves for each of the congeners tested were PCB (PCB-10, PCB-28, PCB-53, PCB-101, PCB-138, PCB-153, PCB-180, PCB-209) in two concentration ranges. The validation of the analytical method included the determination of linearity, standard deviation, relative standard deviation, detection limit (LOD) and limit of quantification (LOQ) of the above PCB congeners. To this end, the development of the methodology for preparing soil samples for chromatographic analysis has been tested for the selection of the extraction method (extraction with solvent assisted by shaking, extraction with ultrasonic assisted solvent, solvent extraction in a Soxhlet apparatus), solvent/solvent system selection (n- hexane, a mixture of n-hexane and dichloromethane in a 1:1 ratio) and selection of sorption material in the SPE solid phase extraction stage (columns for special tasks, Florisil packed columns). Model samples used soil contaminated with the Supelco standard solution number 47330-U. For all the combinations of the above-mentioned conditions of preparing the sample for chromatographic analysis, the recovery rate of individual analytes was calculated. On the basis of chromatographic analyses and recovery levels, the most optimal methodology for preparing soil samples for chromatographic analysis was selected for the determination of polychlorinated biphenyls. The developed methodology for the determination of polychlorinated biphenyls in soil samples was tested on real samples of soils contaminated with aged transformer oil taken from the areas of south-eastern Poland. The analytical procedure for the determination of PCBs in soil samples included: initial sample preparation (drying, milling, homogenization), isolation of analytes from the sample matrix (solvent extraction assisted by shaking with a 1:1 mixture of solvents n-hexane: dichloromethane), sample purification from disturbing substances (a set of two columns for SPE extraction: Silica gel No. 7086-03 and PCB-A No. 7511-04 from Bakerbond), chromatographic analysis. The application of the above-mentioned analytical techniques allowed to obtain information on the content of polychlorinated biphenyls investigated in soils samples.