Determination of Organochlorine Pesticides and Polychlorinated Biphenyls in Grains Using Gas Chromatography with Accelerated Solvent Extraction

The pollution of grains is growing worse due to the soil environment being polluted. The pre-treatment for organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) detected in samples of rice, wheat, corn and soybean is a complicated process with a large amount of solvents, easily leading to volatile compound loss and effects on the accuracy of the analysis. Therefore, choosing a suitable extraction and purification method is very important to the determination of 25 OCPs and PCBs in grains with Gas Chromatography. In this paper, the extraction and purification procedures of this method have been improved greatly by optimizing the parameters of accelerated solvent extraction (ASE) and comparing gel permeation chromatography (GPC) and solid phase extraction (SPE) are described. In addition to soy products, such as soybean and black bean samples needed to be purified by GPC and SPE, most of the rice, wheat, corn and other cereal samples are purified by SPE alone. The sample was extracted with dichloromethane and acetone (V:V=1:1) by ASE (Florisil clean up in the extraction cell), cleaned up by SPE with only 9 mL n-hexane/ethylacetate (V:V=1:1) to recover all the target compounds. The problems of using a large amount of organic reagent and the highly toxic reagent were overcome. The method detection limits of 17 OCPs and 8 PCBs ranged from 0.07 to 0.3 μg/kg, better than the index in national standard method. The average recoveries of 25 OCPs and PCBs were 71.0%-112.0% in the solutions of low and high level contents of 0.69 μg/kg and 5.52 μg/kg. The relative standard deviations (RSDs) for all the compounds were 3.6%-16.7% (n=7). It was confirmed that the method was accurate and credible through determination of spiked rice samples and other grain samples. Compared with traditional methods, this method is simple and convenient to conduct with the advantages of high efficiency, rapidity and low cost. Thereby, it is feasible for the simultaneous determination of OCPs and PCBs in different kinds of grain samples.