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A method of rapid analysis of multi-class residual veterinary drugs in milk, fish and shellfish was validated in accordance with Japanese guidelines for the validation of analytical methods for residual agricultural chemicals in food. Using LC-MS/MS, 43 multi-class veterinary drugs, including sulfonamides, quinolones, coccidiostats and antiparasites, could be analyzed in one injection. Analytes were extracted from samples with two kinds of solvent, acetonitrile containing 1 vol% formic acid and anhydrous acetonitrile, and salted out with 4.0 g of magnesium sulfate, 1.5 g of trisodium citrate and 2.0 g of sodium chloride. This method was assessed by performing recovery tests in retail milk and 4 kinds of fresh cultured fish and shellfish (salmon, tiger shrimp, red sea bream and bastard halibut) spiked with the 43 target analytes at the levels of 10 and 100 μg/kg. Using this method, 40 out of 43 drugs satisfied the guideline criteria in milk, 37 drugs in salmon, 42 drugs in tiger shrimp, 41 drugs in red sea bream and 39 drugs in bastard halibut.

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Residues of 37 polar veterinary drugs belonging to six families (quinolones, tetracyclines, macrolides, lincosamides, sulfonamides, and others) in livestock and fishery products were determined using a validated LC-MS/MS method. There were two key points in sample preparation. First, extraction was performed with two solutions of different polarity. Highly polar compounds were initially extracted with Na2EDTA-McIlvaine's buffer (pH 7.0). Medium polar compounds were then extracted from the same samples with acetonitrile containing 0.1% formic acid. Secondly, cleanup was performed using a single SPE polymer cartridge. The first extracted solution was applied to the cartridge. Highly polar compounds were retained on the cartridge. Then, the second extracted solution was applied to the same cartridge. Both highly and medium polar compounds were eluted from the cartridge. This method satisfied the guideline criteria for 37 out of 37 drugs in swine muscle, chicken muscle, bovine muscle, prawn, salmon trout, red sea bream, milk, and honey; 35 out of 37 in egg; and 34 out of 37 in flounder. The LOQ ranged from 0.1 to 5 μg/kg. Residues were detected in 24 out of 110 samples and analyzed using the validated method.