Determination of Three Benzimidazole Residues in Milk Powder Using HPLC-MS/MS

A method for simultaneous determination of oxfendazole, albendazole and fenbendazole residues in milk powder was developed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). By comparison the extraction effect of different solutions，1% acetic acid-methanol was finally selected as the extracting solution. Two consecutive steps of N-hexane and cationic solid phase extraction were used to remove the interferences in milk powder. Gradient elution programme was performed on a C₁₈ column using a mobile phase consisting of acetonitrile and 0.5 mmol/L ammonium acetate-0.1% formic acid solution. Recoveries of skim milk and whole milk powder are in the range of 70.0%—85.8%. The conrrelation coefficient is greater than 0. 997 3 in the 2—100 μg/L. The method detection limit is 10 μg/kg， and it can be meet all the requirements of national residues level.