Determination of Residues of Diflubenzuron and Chlorbenzuron in Vegetables by High Performance Liquid Chromatography with QuEChERS Purification

After the vegetable samples were cut into small pieces, an aliquot (10.00 g) was taken and mixed with 10 mL of acetonitrile by swirling for 1 min. Anhydrous magnesium sulfate (4.0 g) and sodium chloride (1.0 g) were added, the mixture was whirled for 1 min, and centrifuged for 5 min. An aliquot (1 mL) of the supernatant was taken, and 100 mg of anhydrous magnesium sulfate together with 75 mg of C₁₈ was added, respectively. After whirling for 1 min and centrifuging for 2 min, the supernatant was passed through a 0.22 μ m filter membrane. The filtrate was introduced into high performance liquid chromatograph, and targets were separated on ZORBAX SB-C₁₈ column with acetonitrile-water system at volume ratio of 45:55 under isocratic elution. As shown by the results, the mass concentrations of diflubenzuron and chlorbenzuron were linearly related with their corresponding peak areas in the range of 0.1-5.0 mg·L^-1, with detection limits (3S/N) of 0.007, 0.02 mg·kg^-1, respectively. Six repeated determinations and 6 d continuous determinations on the mixed standard solution were made, and RSDs of the peak areas of diflubenzuron and chlorbenzuron were 0.83%, 1.6% (for intra-day precision test) and 2.5%, 1.8% (for inter-day precision test), respectively. Test for the spiked recovery was made at the 3 concentration levels with cabbage, spinach and cauliflower as matrices, giving recoveries in the range of 87.4%-104% and 75.3%-98.1%. The proposed method was applied to the analysis of 15 samples of three kinds of vegetables, and diflubenzuron was detected in one cauliflower sample, and the detection amount (0.014 mg·kg^-1) was lower than the residue limit (1 mg·kg^-1) stipulated in relevant national standards.