OPTIMIZATION OF A SOLID-PHASE EXTRACTION TECHNIQUE FOR THE EXTRACTIONOF 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 th e method is the formation of a supernatant by sonication of the soil w ith a water-acetone mixture. After removal from the soil particles, th e pesticides are extracted by passing through a disk of octyl-bonded s ilica sorbent. To establish the suitable extraction conditions, severa l variables affecting the performance of the C-8 disk, such as the inf luence of the use of centrifugation or filtration for the removal of s upernatant and soil particles and the effectiveness of the prior sonic ation step, such as water proportion, water temperature and pH of the extractive solution, have been studied. Maximum yields were obtained b y extraction with a mixture of water at 50 degrees C and acetone (1:1) , and centrifugation to remove the supernatant prior to the solid-phas e extraction (SPE). In order to evaluate the matrix effect in SPE of t he pesticides, recovery experiments were performed for soil samples wi th different physical and chemical characteristics.