Determination of 20 Organochlorine Pesticides and 7 Polychloro-Biphenyls in Sediments of Riverbank in Chemical Industry Area by Whole 2- Dimensional Gas Chromatography with Soxhlet Extraction

Sediment from riverbank of polluted area was collected and after picking out those impurities (i.e. branches, leaves, stones etc.) which were mixed up in, it was mixed thoroughly and ready to be used as analytical sample. 10.00 g of the sample were taken and mixed thoroughly with an appropriate amount of anhydrous Na₂SO₄, which has been baked at 400℃ for 4 h beforehand, and then ground to fine powdery state. The powder mixture was loaded completely into a sleeve made of filter paper, and the sleeve was replaced into the Soxhlet extractor, and extracted with 250 mL of a mixed solution of n-hexane and acetone with the volume ratio of 1:1 for 8-12 h at a refluxing rate of 10 times perhour (the authors propose to arrange the soxhlet extraction overnight in batches, by automation). The extracts were collected, combined and mixed thoroughly. A pre-activated copper sheet was placed into the combined extract for 4-6 h to eliminate sulfide by precipitation of sulfide on the copper sheet. The solution mixture was then filtered, and the filtrate was concentrated to a smaller volume and purified by passing through SPE column packed with Florisil. The analytes were adsorbed on SPE column and were eluted from the column by 15 mL of a mixed solution of n-hexane and acetone with the volume ratio of 9:1. The eluate was collected and evaporated to a definite volume 1.0 mL in which 27 compoundsi.e. 20 organochlorine pesticides (OCPs) and 7 polychloro-biphenyls (PCBs) were contained and be further separated and determined with ECD. In the 2-dimensional gas chromatography separation, 2 chromatographic columns, i.e. the non-polar column (TG-35MS, the 1 st D) and the polar column (DB-1, the 2nd D) were used in combination. Among the 27 compounds, non-polar compounds were separated according to their differences in boiling points on the 1st D-column; the eluate from which was modulated by focusing to elevate its temperature rapidly (with gap of modulation of 4 s) and introduced into 2nd D-column through which the analysts with differences in polarities were separated. Good separation of the 27 compounds was attained by this arrangement. Linear relationships between values of mass concentration of the 27 compounds and their respective peak areas were found in the same range of 1.0-200.0 μg·L^-1; with their detection limits (3.14 s) in the range of 0.017-0.087 μg·kg^-1. Test for recovery was made by standard addition method, the results of recovery were found ranged from 72.0% to 96.3%, and values of RSDs (n=6) were found in the range from 2.1% to 11%.