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 μg/kg(β-agonist and triphenylmethane), 1.0 μg/kg(benzodiazepine and nitroimdazole), 5.0 μg/kg(benzimidazole) and 20.0 μg/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 μg/kg.

Abstract A method based on dispersive solid phase extraction-high performance liquid chromatography-tandem mass spectrometry for determination of 19 kinds of nonprotein nitrogen compounds including melamine, cyromazine, amidinourea, aminotriazine, 3-aminotriazole, 4-aminotriazole, allantoin, cyanuric acid, dicyandiamide, thiourea, semicarbazide, L-leucine, L-isoleucine, L-arginine, L-hydroxyproline, L-theanine, ammeline, ammelide and guanidine in powdered formulas was presented. The nonprotein nitrogen compounds were degreased by chloroform and extracted by acetonitrile, with MgSO4 to remove water and C18 to clean up. The samples were separated on Merck ZIC HILIC column (150 mm í2. 1 mm, 5 μm, 20 nm) with gradient elution. The electrospray ionization was operated in the positive mode and negative mode, and monitored by the multiple reaction monitoring ( MRM) mode. Allation was quantified by external standard method and the other 18 kinds of nonprotein nitrogen compounds were quantified by internal standard method. All of the correlation coefficients (r) were higher than 0. 99. The limits of quantitation (LOQ) were 0. 05-5. 0 mg/kg, the average recoveries were between 82 . 2% and 115 . 0%, and the relative standard deviations were less than 20%.