Matrix effects on solid-phase microextraction of organophosphorus pesticides from water

This study develops a method for solid-phase microextraction (SPME) of eight organophosphorus pesticides, diazinon, fenthion, fenitrothion (sumithion), methyl-parathion, parathion, methyl-trithion, ethion and triazophos, from water. Determination is carried out by gas chromatography with nitrogen-phosphorus detection. To perform the SPME, poly(dimethylsiloxane) and polyacrylate fibers were initially compared on the basis of their absorption capacities for the selected pesticides, and polyacrylate was selected to accomplish the rest of assays. The main factors affecting the SPME process such as memory effect, stirring late, extraction temperature and absorption-time profile were studied. The proposed method requires 2 ml of sample and reaches limits of detection ranging between 6 ng/l for fenthion and 136 ng/l for methyl-parathion, with relative standard deviations at the 500 ng/l level between 2% for diazinon and 13% for ethion. The method was applied to spiked tapwater, seawater, wastewater with high dissolved organic matter content (DOC=212 mg/l) and water containing 15 mg/l of sodium lauryl sulfate (SDS), which were previously analyzed to control interferences. Recoveries for diazinon, fenthion and methyl-trithion were better from seawater than from Milli-Q water. Recoveries for fenthion and ethion increased with the presence of SDS and those for methyl-parathion and triazophos decreased from the wastewater because of the presence of the organic matter. Finally, a wastewater from a pesticide producer industry was analyzed showing the presence of diazinon and ethion at concentrations of 0.97 mu g/l and 0.67 mu g/l, respectively. Results were in concordance with those obtained using a standard liquid-liquid extraction method.