Development and Validation of an HPLC Method for Determination of Thiamethoxam and Its Metabolites in Cotton Leaves and Soil

An easy and simple analytical method was standardized and validated for the estimation of residues of thiamethoxam and its metabolites in cotton. The samples were extracted with acetonitrile, water, and methanol; diluted with brine solution; partitioned into dichloromethane and ethyl acetate; dried over anhydrous sodium sulfate; and cleaned up by glass column chromatography. Final clear extracts were concentrated under vacuum and reconstituted into HPLC grade acetonitrile, and residues were estimated using an HPLC instrument equipped with a C18 column and photodiode array detector system. Acetonitrile-1% formic acid in HPLC grade water (30 + 70) was used as mobile phase at 0.2 mL/min. Consistent recoveries ranging from 82 to 97% for thiamethoxam and its metabolites were observed when samples were spiked at 0.05-1.0 mg/kg levels. The LOQ of the method was determined to be 0.05 mg/kg. The analytical method was validated in terms of the selectivity, linearity, precision, and accuracy of the detection system.