Optimization of a solid-phase extraction technique for the extraction of pesticides from soil samples

Progress has been made towards optimizing a rapid, accurate method for extracting pesticides from soil for routine analyses. The basis of the method is the formation of a supernatant by sonication of the soil with a water-acetone mixture. After removal from the soil particles, the pesticides are extracted by passing through a disk of octyl-bonded silica sorbent. To establish the suitable extraction conditions, several variables affecting the performance of the C-8 disk, such as the influence of the use of centrifugation or filtration for the removal of supernatant and soil particles and the effectiveness of the prior sonication step, such as water proportion, water temperature and pH of the extractive solution, have been studied. Maximum yields were obtained by extraction with a mixture of water at 50 degrees C and acetone (1:1), and centrifugation to remove the supernatant prior to the solid-phase extraction (SPE). In order to evaluate the matrix effect in SPE of the pesticides, recovery experiments were performed for soil samples with different physical and chemical characteristics.