Development of methods for determination of the residues of 15 pesticides in medicinal herbs Isatis indigotica Fort. by capillary gas chromatography with electron capture or flame photometric detection

Two multiresidue methods were developed for the determination of 15 pesticides (organochlorines, organphosphorus compounds, pyrethroids, and fungicides) in medicinal herbs Isatis indigotica Fort. and its formulations. The analytical procedure is based on ultrasonic assisted extraction and liquid-liquid extraction (LLE). After solvents were added, the raw material or granule sample was sonicated in an ultrasonic water bath and then centrifuged, filtered, and cleaned up by LLE. The infusion sample was extracted with petroleum ether by LLE. The pesticide residues were determined by capillary gas chromatography with electron-capture or flame photometric detection. Recoveries with the method at concentrations between 0.4 microg/kg and 10 mg/kg ranged from 70.2 to 119.5% for raw material, 73.2 to 105.1% for granule formulation, and 72.8 to 113.3% for infusion formulation. The relative standard deviation values were <20% for all of the pesticides studied. The pesticide detection limits were within the ranges 0.3-0.5 microg/L for endosulfan, 3-7.5 microg/L for pyrethroids, 0.7-32.5 microg/L for organophosphorus pesticides, and 0.1-0.6 microg/L for the other pesticides. The proposed methods are simple and rapid and provide simultaneous determination of pesticide residues in Isatis indigotica Fort. with acceptable recoveries and repeatability and an adequate limit of determination.