Determination of Organophosphorus Pesticides in Groundwater by Gas Chromatography Coupled with Closed Ultrasound Circulating Purge Needle Trap

Based on the merits of solvent-free extraction of gaseous samples by needle trap, closed circulating purge system consisting of needle trap and water sample by peristaltic pump is established to enhance the Henry's law constant of analytes in the gas/liquid phase. In this study, the method for determination of dichlorvos, phorate, methyl parathion and malathion in groundwater by circulating extraction with needle trap coupled with Gas Chromatography was established. This method integrated sampling, extraction, purification, concentration, and chromatography. The optimum conditions for the extraction by needle trap include sampling flow rate of 11.11 mL/min and extraction temperature of 40℃. Under these conditions, the maximum breakthrough volume of 1 mg/L methyl parathion is 600 mL. The recoveries range from 62.3% to 103.0% for 5 μg/L, 50 μg/L and 200 μg/L analytes. Low level dichlorvos has a relative standard deviation of 26.1%, and other components are lower than 7.7%. The detection limits of the proposed method range from 0.016 to 0.157 μg/L, close to, or better than the current standard results and related study results.