Abstract: An ultra high performance liquid chromatography-tandem mass spectrometry （UPLC-MS/MS） method was established for the simultaneous detection of 55 types of antibacterial drugs, including sulfonamides, macrolides, and quinolones, in organic fertilizer.After grinding and sieving the organic fertilizer into experimental samples, they were purified using HLB solid-phase extraction column. After loading, the samples were sequentially washed with deionized water and 5% acetonitrile aqueous solution, eluted with methanol/ethyl acetate solution （volume ratio 7∶3, containing 5% ammonia）, blown dry with nitrogen, and re-dissolved in 0.1% formic acid water/acetonitrile （volume ratio 9∶1）;measurement was carried out in a multi reaction detection mode, with the external standard method for quantification. The results showed that among the four batches of organic fertilizers, 55 drugs had a good linear relationship （R²>0.990） within the range of 1.0~100 μg/kg,the detection limit of this method was 2.0~7.5 μg/kg,the quantitative limit was 5.0~25.0 μg/kg,the recovery rates of various drugs were 60.2%~118.7%,the relative standard deviation within the batch （n=5） was 0.5%~15.0%, and the relative standard deviation between batches （n=20） was 4.3%~24.1%. This method was simple and reliable, with a good purification effect, and was suitable for the simultaneous detection of sulfonamide, quinolone, and macrocyclic lipid drugs in organic fertilizer.

Key words: organic fertilizer, UPLC-MS/MS, rapid detection, antibacterial drugs