Microwave-assisted extraction of pyrethroid insecticides from soil

An analytical method has been developed for the microwave-assisted extraction of synthetic pyrethroid insecticide residues in soils and their determination by gas chromatography with electron capture detector (ECD) and mass spectrometry (MS) detector. Clean soil samples were spiked with nine pyrethroids: tetramethrin, cyfluthrin, flucythrinate, deltamethrin, bifenthrin, permethrin, cypermethrin and fluvalinate were used for this study. Concentration levels were 50 ng g−1 for all the compounds studied except to sumitrin for which a 10 μg g−1 was evaluated. Two grams of sample were treated in a closed PTFE reactor with 10 mL toluene and 1 mL water and irradiated at 700 W during 9 min. The toluene extract was evaporated and reconstituted in 2 mL hexane and copper wires added in order to remove sulphur interferences. Clean-up with 2 g of florisil and elution with 20 mL ethyl acetate:hexane 33% (v/v) was performed. Best chromatographic conditions were established for GC-ECD analysis for routine analysis and GC-NCI-MS for confirmation. Recovery yields of spiked soils were from 97 to 106% for eight of the pyrethroid and 86% for the tetramethrin, with relative standard deviations from 1 to 7%. Results were comparable with those found by ultrasonic extraction in the analysis of real samples and limit of detection values obtained were in the range from 1 to 200 ng/g for ECD and from 0.3 to 2 ng/g for NCI-MS.