Determination of diflubenzuron in apples by gas chromatography

A method for the determination of residues of the insecticide diflubenzuron, 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea, in apples using gas chromatography with electron-capture detection has been developed and validated. The three solvents ethyl acetate, acetone and dichloromethane were tested for extraction of diflubenzuron residues from apples. Dichloromethane gave the highest recovery and the lowest background and was chosen as the extraction solvent. After extraction the residue of diflubenzuron was derivatized with heptafluorobutyric anhydride. The derivative was purified by silica solid-phase extraction using toluene as the eluent. The external standard calibration was linear over the range 0.05-1.0 mu g/ml and the limit of quantification was 0.03 mg/kg apple using 25 g samples. Recovery of diflubenzuron from spiked apples (0.1-0.8 mg/kg) was 80-88% with a relative standard deviation of less than 10% (n=5). The method was applied to the determination of diflubenzuron residues in apples from a treated field.