Multiresidue analysis of carbamate pesticides in soil by sonication-assisted extraction in small columns and liquid chromatography

A rapid multiresidue method has been developed for the analysis of carbamate insecticides (oxamyl, methomyl, propoxur, carbofuran, carbaryl and methiocarb) in soil. The method is based on the sonication-assisted extraction of soil samples placed in small columns using a low volume of methanol. Residue levels in soil were determined by reversed-phase high-performance liquid chromatography with fluorescence detection after post-column derivatisation. The separation of carbamates is performed on a C8 column with water–methanol as mobile phase. Recovery studies were carried out at 0.5, 0.1 and 0.01 μg/g fortification levels and average recoveries obtained for carbamates ranged from 82 to 99% with relative standard deviations between 0.4 and 10%. The effect of residue residence time and soil moisture content on the insecticide recovery was also studied. The method is linear over the range assayed, from 0.1 to 1 μg/ml. The detection limit for the carbamates varied from 1.6 to 3.7 μg/kg and the quantification limit obtained was 10 μg/kg. The emission and excitation spectra allowed the confirmation of residues at levels around 0.1 μg/g.