Focused Microwave Assistance for Extracting Some Pesticide Residues from Strawberries into Water before Their Determination by SPME/HPLC/DAD

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Abstract
A novel and simple method for the determination of some pesticide residues in strawberries using both focused microwave-assisted extraction (FMAE) and solid-phase micro extraction (SPME), coupled with high-performance liquid chromatography (HPLC), has been developed. The pesticides were first extracted from strawberries with water and the assistance of focused microwaves at 30 W for 7 min. Then, an aliquot of the resulting aqueous extract was subjected to SPME with a 60-μm thick poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fiber for 45 min at room temperature, with the solution being stirred at 1000 rpm. The extracted pesticides on the SPME fiber were desorbed into the SPME/HPLC interface for quantitative analysis with a diode array detector (DAD). The whole sample pretreatment procedure before chromatographic analysis did not use any organic solvents or involve any blending or centrifugation steps. The five compounds (carbendazim, diethofencarb, azoxystrobine, napropamide, and bupirimate) were chosen because they cannot be analyzed easily by GC. The efficiency of this relatively fast procedure was comparable to that of previously reported methods, with detection limits at low μg/kg levels and linear responses in the range from 0.05 to 1 mg/kg of pesticide in strawberries, with RSDs between 3 and 7.3%, depending on the analyte. In all but one case results obtained by this method for field-incurred samples were comparable to those obtained with traditional methods. Keywords: Focused microwave-assisted extraction; solid-phase micro-extraction; pesticide residues; strawberries; high-performance liquid chromatography

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