Simultaneous Determination of Residues of Four Typical Categories of Veterinary Antibiotics in Organic Fertilizers

A new method using SPE-UPLC-MS/MS was developed to determine residues of four typical categories of veterinary antibiotics in organic manure. The method uses the solution composed of acetonitrile and phosphate buffer (pH=3) for extraction of organic manure samples, and the series of SAX and HLB to purify and enrich the extract. Methanol-φ=0.1% formic acid was chosen as carrier for liquid chromatographic analysis. When the concentrations of the 18 antibiotics were in the range of 5-500µg•kg^-1, they showed good linear relationships, with determination coefficients (r²) ≥ 0.99. When the mass concentration of the antibiotics was raised to the range of 50-500µg•kg^-1, the recovery rates of sulfonamides, fluoroquinolones, tetracyclines and macrolides varied in the range from 71.6% to 94.3%, from 72.3% to 86.7%, from 71.0% to 102.2% and from 70.7% to 93.3%, respectively, with relative standard deviation varying in the range of from 2.1% to 11.4%. This method was applied to determine residues of veterinary antibiotics in organic fertilizers on sale in Nanjing. In addition to sulfonamides, others were also detected to a varying extent.