Study On The Rapid Analysis Method Of UPLC-QDa Simultaneous Detection Of Veterinary Drug Residues Of Various Antimicrobials In Milk

Objective In animal husbandry,antimicrobial drugs are widely used in the treatment of various diseases of dairy cows,resulting in the presence of dairy exogenous antibiotics,causing great harm to human health.It is particularly important to establish and optimize a rapid analysis method for rapid detection and analysis of trace amounts of veterinary drug residues in milk.In this study,an ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-QDa)method for the determination of six antimicrobial agents in milk was established.The method can meet the trace requirements of veterinary antimicrobial drugs commonly used in daily milk.Methods First,the conditions of ultra performance liquid chromatography and QDa mass spectrometry were optimized.Secondly,the pre-treatment method of the sample is optimized.The concrete steps are as follows:Accurately weigh 5.0 g of the milk sample in a 50 mL centrifuge tube,add 5 mL of PBS buffer solution(pH 7.0),vortex and mix for 1.5 min,add 7.0 mL of acetonitrile,1.0 g of sodium chloride,2.0 g of anhydrous sulfuric acid Sodium,30 ℃ water bath for 5 min,vortex mixing 3 min,5500 r/min high speed centrifugation 6 min,take the supernatant in 10 mL scale glass tube.The milk that after being centrifuged,add 3.0 mL of acetonitrile again,repeat the above procedure(without adding sodium chloride and anhydrous sodium sulfate),the supernatant was combined and was blown the nitrogen to near dry at 30℃.Add 5 mL of water to dissolve and wait for the sample to be treated.The HLB solid phase extraction column was pretreated with 6 mL of methanol and 6 mL of water,The extract was added to the column,eluted with 6 mL of water,eluted with 10 mL of eluent(methanol-ethyl acetate 7/3,V/V),and kept the flow rate 1-2 mL/min,until the eluent flowed out completely.The eluate was collected at 10 mL glass scale tube and dried at 30℃ under nitrogen.Add 1 mL of methanol,vortex 1 min,over 0.22 μm filter for analysis.Finally,the commercially available milk was tested using the established method.Results The linearity of the six mixed standard samples was 10～250 μg/L;The limit of detection(calculated according to S/N=3)and the limit of quantitation(calculated according to S/N=10)were studied with fresh milk blank matrix.The limit of detection was 1.5～6 μg/kg;the limit of quantitation was 5-20 μg/kg.Respectively,with a limit of quantitation,5 times the limit of quantitation and 10 times the limit of quantitation as the three addition levels,each level of addition to do 5 parallel tests,the average recoveries of all the target compounds ranged from 72.1%to 95.0%,and the relative standard deviations ranged from 1.31%to 13.8%.Conclusion In this study,an ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-QDa)method was established for the determination of three kinds of nitroimidazoles,two kinds of macrolides and one kind of amides antibiotics veterinary drug residues in milk.The pretreatment conditions of the sample were optimized.The method was simple to operate and has a high sensitivity.