Studies On Sample Pretreatment Methods Of Multi-class Veterinary Drugs Residues In Chicken Muscle Based On LC-MS/MS Analysis

Simple,sensitive,scientific and reliable liquid chromatography-tandem mass spectrometry methods were successfully developed for the simultaneous determination of multi-class veterinary drugs including sulfaquinoxaline,enrofloxacin,ciprofloxacin,kitasamycin,tiamulin,dexamethasone,metronidazoleand3-methylquinoxaline-2-carboxylic acid?the marker residue of olaquindox?in chicken muscle samples based on freeze-thaw,lyphilization and alkaline hydrolysis approaches,respectively.Freeze-thaw and lyophilization sample pretreatment methods were developed to determine seven veterinary drug residues in chicken muscle tissue.Based on freeze-thaw strategy,chicken samples were frozen at-20?for 6 hours and then thawed at room temperature.Based on lyophilization strategy,chicken samples were lyophilized and then rehydrated.The freeze-thawing and lyophilized samples were separately extracted with 1%acetate in acetonitrile,centrifuged,and the supernatant was diluted by 20%methanol in water containing 0.1%formic acid before analysis using liquid chromatography-tandem mass spectrometry?LC-MS/MS?.Target analytes were quantified using the matrix-matched calibration curves,the seven drugs showed good linearity within experimental concentration ranges,and the correlation coefficients were greater than 0.99.At the three spiked levels of 10,50,and 100?g·kg^-1(dexamethasone and metronidazole:2,5 and 10?g·kg^-1),the average recoveries of the seven drugs were 75.7%¹08.4%and the relative standard deviation?RSD?was in 0.4%¹7.0%.The limits of detection and limits of quantification of analytes ranged from 0.04 to 0.8?g·kg^-1 and 0.1 to 2.0?g·kg^-1,respectively.The statistical analysis shows that the amounts of metronidazole obtained by using freeze-thaw method is significantly higher than that obtained by the national standard method,but the difference between the results of the other 6 drugs is not significant,and the difference of all the results of the lyophilization method is not significant,which shows that the freeze-thaw method and lyophilization method may replace the traditional pretreatment methods.The proposed method could be used to analyze the residues of veterinary drugs in animal muscle tissue,which greatly simplifies the pretreatment process.Based on alkaline hydrolysis,a simple,reproducible and scientific LC-MS/MS method was developed to determine the marker residue 3-methylquinoxaline-2-carboxylic acid?MQCA?of olaquindox in chicken muscle tissue.Chicken was medicated with olaquindox,and three sample pretreatment approaches such as enzyme,acid and base hydrolysis,were adopted to digest MQCA in chicken muscle.The amounts of MQCA in medicated chicken were determined and compared by using three hydrolysis approaches.It was shown that the highest amount value of MQCA was obtained by using base hydrolysis approach.Sample was hydrolyzed with 1.0 mol·L^-1 NaOH solution,defatted with n-hexane,and then the lower solution was directly purified by a mixed anion-exchange?MAX?solid-phase extraction cartridge.The chromatographic separation was performed on a reversed-phase C₁₈ column and detected by mass spectrometry in selected reaction monitoring mode.The analyte showed good linearity in the range of 1.0¹00?g·L^-1.The correlation coefficient?r²?was more than 0.99.At three spiked concentration levels of 1.0,5.0 and 50.0?g·kg^-1,the average recoveries of MQCA were in range of 71.7%⁸2.4%?the external standard method?and 96.3%and 103.7%?the internal standard method?with the relative standard deviation?RSD?below 6.0%.The limit of detection and limit of quantification of the method were 0.4?g·kg^-1 and 1.0?g·kg^-1,respectively.The proposed method is more convenient,reasonable and effective than the methods in the literature.It is suitable for routinely monitoring of 3-methyl quinoline-2-carboxylic acid residues in animal food.