Determination of Residues of Oxine-Copper in Citrus by HPLC

Citrus samples were randomly picked, manually separated, homogenized and reduced, and an aliquot (5.00 g) of citrus whole fruit, flesh and peel was taken respectively. The mixed solution (mobile phase, 10 mL) of 0.1% (volume fraction) trifluoroacetic acid solution and acetonitrile at volume ratio of 1:9 and 3.0 g of sodium chloride were added into the samples, the mixture was treated by vortex mixing for 5 min, ultrasonic extraction for 20 min and centrifugation for 5 min, and the extraction was repeated once again. The supernatants obtained were combined, an aliquot (5 mL) was purified by 5 mg of GCB. After centrifugation for 5 min, 4 mL of the supernatant was evaporated by rotation to nearly dry. The residue was redissolved by 1 mL of mobile phase, filtered by a 0.22 μm aqueous phase filtration membrane, and analyzed by HPLC. The target compound was separated on SunFire^® C₁₈ column with mobile phase by isocratic elution, and detected at wavelength of 254 nm. It was shown that linear relationship between values of mass concentration of oxine-copper and its peak area was kept in the range of 0.1-5.0 mg·L^-1, with detection limit of 0.1 mg·kg^-1. Test for the spiked recovery was made at three concentration levels with negative citrus whole fruit, flesh and peel as matrices, giving recoveries in the range of 83.6%-95.6%, and RSDs (n=5) of the determined values ranged from 2.3% to 6.7%. The proposed method was applied to the analysis of actual samples, oxine-copper was not detected, and the residue of oxine-copper could be detected in citrus samples of whole fruit and peel after spraying at the recommended dose for 2 h.