Determination of phenolic and salicylanilide anthelmintics in liquid milk by high performance liquid chromatography

An analytical method for the determination of nitroxynil, oxyclozanide, closantel and rafoxanide in liquid milk by high performance liquid chromatography (HPLC) has been established. The milk sample was extracted with acetonitrile containing 1% (v/v) triethylamine. The supernatant was purified by an anion exchange solid phase extraction column. The analyte was detected by ultraviolet detector after the HPLC separation on a C18 RP column. The mobile phase was composed of acetonitrile-0.02 mol/L ammonium acetate solution with pH 4.0. The linear ranges of the four drugs in the spiked blank milk samples were 5-500 microg/kg, and the correlation coefficients were higher than 0.99. The limits of detection (LOD) were 3 microg/kg, and the limits of quantification (LOQ) were 5 microg/kg. The average recoveries and relative standard deviations (RSDs) of nitroxynil, oxyclozanide, closantel and rafoxanide at the spiked levels of 1/2MRL (maximum residue limit), MRL and 2MRL ranged from 92.20% to 96.13%, 5.55% to 16.30%; 87.40% to 94.74%, 5.40% to 12.21%; 86.97% to 91.09%, 2.67% to 8.17%; and 77.86% to 95.36%, 5.02% to 13.15% respectively. The method is simple and sensitive for the quantification of phenolic and salicylanilide anthelmintics in liquid milk.