Multiresidue Determination of Pesticides in Soil by Gas Chromatography−Mass Spectrometry Detection

An analytical multiresidue method for the simultaneous determination of various classes of pesticides in soil was developed. Pesticides were extracted from soil with ethyl acetate. Soil samples were placed in small columns, and the extraction was carried out assisted by sonication. Pesticides were determined by gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode. Spiked blank samples were used as standards to counteract the matrix effect observed in the chromatographic determination. Pesticides were confirmed by their retention times, their qualifier and target ions, and their qualifier/target abundance ratios. Recovery studies were performed at 0.2, 0.1, and 0.05 microg/g fortification levels of each pesticide, and the recoveries obtained ranged from 87.0 to 106.2% with a relative standard deviation between 2.4 and 10.6%. Good resolution of the pesticide mixture was achieved in approximately 41 min. The detection limits of the method ranged from 0.02 to 1.6 microg/kg for the different pesticides studied. The developed method is linear over the range assayed, 25-1000 microg/L, with determination coefficients >0.999. The proposed method was used to determine pesticide levels in real soil samples, taken from different agricultural areas of Spain, where several herbicides and insecticides were found.