Determination of anthelmintic residues in milk by high performance liquid chromatography

The optimisation and validation of two HPLC methods to determine anthelmintic drugs in milk is described. Satisfactory analytical separations and detection limits were obtained with ion-pairing liquid chromatography and diode array detection at 225 nm for levamisole and at 295 nm for fenbendazole, thiabendazole, albendazole and oxibendazole. The mean extraction recoveries ranged from 68% to 85%. The limits of detection for fenbendazole, thiabendazole, albendazole, oxibendazole and levamisole were 3.1, 3.4, 3.8, 1.3 and 0.5 ng/ml, respectively. The limits of quantification for these anthelmintics were 6.8, 4.3, 6.9, 2.7 and 1.4 ng/ml, respectively. The over-all precision data, based on within and between day variations during three days for the above mentioned drugs were 11.9%, 3.9%, 8.2%, 7.4% and 12.7%. The method for levamisole was successfully applied to quantify residue values in milk samples collected from excretion studies with cows. The cows were treated topically twice with a dose of 10 or 20 mg levamisole per kilogram body weight. 79 h after treatment, the mean levamisole concentration had declined to 21 and 83 ng/ml, respectively.