Determination of pesticides in soil by liquid-phase microextraction and gas chromatography–mass spectrometry

Trace amounts of pesticides in soil were determined by liquid-phase microextraction (LPME) coupled to gas chromatography–mass spectrometry (GC–MS). The technique involved the use of a small amount (3 μl) of organic solvent impregnated in a hollow fiber membrane, which was attached to the needle of a conventional GC syringe. The organic solvent was repeatedly discharged into and withdrawn from the porous polypropylene hollow fiber by a syringe pump, with the pesticides being extracted from a 4 ml aqueous soil sample into the organic solvent within the hollow fiber. Aspects of the developed procedure such as organic solvent selection, extraction time, movement pattern of plunger, concentrations of humic acid and salt, and the proportion of organic solvent in the soil sample, were optimized. Limits of detection (LOD) were between 0.05 and 0.1 μg/g with GC–MS analysis under selected-ion monitoring (SIM). Also, this method provided good precision ranging from 6 to 13%; the relative standard deviations were lower than 10% for most target pesticides (at spiked levels of 0.5 μg/g in aqueous soil sample). Finally, the results were compared to those achieved using solid-phase microextraction (SPME). The results demonstrated that LPME was a fast (within 4 min) and accurate method to determine trace amounts of pesticides in soil.