Simultaneous Determination of 76 Veterinary Drug Residues in Foodstuffs of Animal Origin by Solid Phase Extraction-Liquid Chromatography-Tandem Mass Spectrometry

A method based on solid phase extraction-liquid chromatography-tandem mass spectrometry for the simultaneous determination of 76 veterinary drugs in foodstuffs of animal origin was presented. The residues derived from pork, shrimp, milk, liver and egg were extracted by acetonitrile combined with citrate buffer containing magnesium cation. The extracts were distilled and redissolved with citrate buffer followed by a further cleanup procedure using polymer connected with cation exchange SPE column. The residues retained in column were rinsed with methanol and mixture of methanol and ammonium hydroxide (95:5, V/V). Sample matrix-matched calibration was used to determine the residue contents by external standard. The method provided a LOQ of 0.5 mu g/kg (beta-agonist and triphenylmethane), 1.0 mu g/kg (benzodiazepine and nitroimdazole), 5.0 mu g/kg( benzimidazole) and 20.0 mu g/kg( sulfanilamide), linear relationship more than 0.907 and a recovery ranged from 59.4% to 115.3% with a RSD between 2.6% and 27.3% in sample matrix. The practical inspection using the method offered two positive samples for ractopamine and diazepam with a residual concentration of 0.92 and 6.5 mu g/kg.