SPE-HPLC Determination of Residual Amounts of 19 Pesticides in Soil

Sample of soil (5.000 g) was extracted ultrasonically twice with mixed solvent of acetonitrile and water (80+20) (20 mL for each extraction) for 20 min. The extracts were filtered into a 100 mL cyclinder with stopper, in which 3 g of NaCl were added previously. The mixture was shaked vigorously for 1 min and stayed for 10 min to have the phases of acetonitrile and water separated. Ten mL of the supernatant acetonitrile solution were taken and evaporated to 0.5 mL by blowing with nitrogen at 40 ℃. Four mL of pure water were added, and purified by passing through activated C18 SPE microcolumn. Methanol (4 mL) was used as eluant and the eluate was evaporated by N2-blowing to 1.5 mL which were used for HPLC analysis. C18 chromatographic column was used as stationary phase and mixtures of acetonitrile and water of various proportions were used as mobile phase in the gradient elution. The 19 pecticides were determined in various time intervals and at various wavelengths in UV-region as described in the gradient elution program. Detection limits found were in the range of 0.001 to 0.15 mg·kg-1. Values of recovery found were ranged from 70.1% to 117.9%.