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 t riazophos, from water. Determination is carried out by gas chromatogra phy with nitrogen-phosphorus detection. To perform the SPME, poly(dime thylsiloxane) and polyacrylate fibers were initially compared on the b asis of their absorption capacities for the selected pesticides, and p olyacrylate was selected to accomplish the rest of assays. The main fa ctors 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 detectio n ranging between 6 ng/l for fenthion and 136 ng/l for methyl-parathio n, with relative standard deviations at the 500 ng/l level between 2% for diazinon and 13% for ethion. The method was applied to spiked tapw ater, 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. Recover ies for diazinon, fenthion and methyl-trithion were better from seawat er than from Milli-Q water. Recoveries for fenthion and ethion increas ed with the presence of SDS and those for methyl-parathion and triazop hos decreased from the wastewater because of the presence of the organ ic matter. Finally, a wastewater from a pesticide producer industry wa s analyzed showing the presence of diazinon and ethion at concentratio ns of 0.97 mu g/l and 0.67 mu g/l, respectively. Results were in conco rdance with those obtained using a standard liquid-liquid extraction m ethod.