| Both enrofloxacin and ofloxacin are commonly utilised fluoroquinolones in livestock and poultry production.Improper and overuse of them in foods of animal origin can result in excessive residual levels,which could have negative effects on human health.At present,there is no report on the simultaneous detection of enrofloxacin and ofloxacin residues in foods of animal origin by gas chromatography-tandem mass spectrometry(GC-MS/MS).In this experiment,Shaobo chicken and Duroc-landrace-yorkshire swine were used as test materials,and a GC-MS/MS method was developed for the determination of enrofloxacin and ofloxacin residues in chicken tissues(muscle,liver,kidney),pork and eggs(whole egg,albumen,yolk)using liquid-liquid extraction(LLE)in combination with solid-phase extraction(SPE).The primary results can be summarised as follows:1.The derivatization reactions of enrofloxacin and ofloxacin with trimethylsilyldiazome-thane(TMSD)were established,and their derivatives,namely enrofloxacin trimethylsilyl ester and ofloxacin trimethylsilyl ester,were identified.100 μL of enrofloxacin(1.0 μg/mL)and ofloxacin(0.1 μg/mL)mixed standard working solution was accurately measured in a 10 mL centrifuge tube,to which 200 μL of TMSD was added,and the reaction was performed for 30 min at room temperature and shielded from light,then,enrofloxacin trimethylsilyl ester and ofloxacin trimethylsilyl ester were produced.2.A LLE combined with SPE was developed for the extraction of enrofloxacin and ofloxacin residues in chicken tissues,pork and eggs.The 2(±0.02)g sample was precisely weighed,extracted using 5 mL of 2%formic acid acetonitrile,repeated once,and then purified using Oasis PRiME HLB column(3 cc/60 mg)after being degreased with acetonitrile saturated n-hexane.The recoveries were all greater than 78.25%,which significantly reduced the matrix effect of substrate impact on the results of this experiment.3.A confirmatory analytical method was established for the simultaneous determination of enrofloxacin and ofloxacin residues in chicken tissues,pork,and eggs by pre-column derivatization-GC-MS/MS.EI mode,Full SCAN was employed for characterization and Auto SRM optimization combined with the external standard method for quantification.The findings revealed that the peak areas of the characteristic ion mass chromatograms and matrixmatched standard solutions were in the range of 3.2～1600.0 ng/mL for matrix-matched enrofloxacin in chicken muscle and pork,3.8～1600.0 ng/mL for matrix-matched enrofloxacin in chicken liver,and 3.4～1600.0 ng/mL for matrix-matched enrofloxacin in the chicken kidney.The linear relationship was good with the coefficient of determination R2≥0.9991;the linear relationship between the characteristic ion mass chromatographic peak areas and the concentrations of the matrix-matched standard solution was good for chicken muscle;chicken kidney and pork matrix-matched ofloxacin standard solutions were in the range of 0.6～160.0 ng/mL;chicken liver matrix-matched ofloxacin standard solutions was in the range of 0.8～160.0 ng/mL,R2≥0.9990.A good linear relationship exists between the peak area of the characteristic ion mass chromatography and the concentration of the matrix-matched standard solution,which was in the range of 2.6～400.0 ng/mL for chicken whole egg matrix-matched enrofloxacin,2.0～400.0 ng/mL for egg albumen matrix-matched enrofloxacin,and 3.0～400.0 ng/mL for egg yolk matrix-matched enrofloxacin.The linear relationship was good between the peak areas of the characteristic ion mass chromatograms as well as the concentrations of matrix-matched standard solutions,with R2≥0.9991;the peak areas of the characteristic ion mass chromatograms were linear and in the range of 0.6～40.0 ng/mL for whole chicken eggs,0.4～40.0 ng/mL for egg albumen,and 0.8～40.0 ng/mL for egg yolk.The linear relationship was strong with R2≥0.9991.When enrofloxacin and ofloxacin were added to blank samples at concentrations of LOQ,0.5 MRL(Maximum residue limit),1 MRL,and 2 MRL,the recoveries of enrofloxacin and ofloxacin in chicken tissues and pork were 78.25%～90.56%and 78.43%～91.86%,respectively;the intra-day RSDs were 1.86%～4.84%and 2.32%～4.19%,respectively;the inter-day RSDs were 2.58%～5.76%and 2.70%～5.26%,respectively;LODs were 0.7～1.0 μg/kg and 0.1～0.2 g/kg,respectively;LOQs were 1.6～1.9 μg/kg and 0.3～0.4μg/kg,respectively.The recoveries of enrofloxacin and ofloxacin spiked in eggs were 79.78%～92.33%and 78.26%～90.79%,respectively;the intra-day RSDs were 2.18%～4.32%and 2.62%～3.89%,respectively;the inter-day RSDs were 2.66%～5.17%and 3.24%～4.81%,respectively;the LODs were 0.4～0.8 μg/kg,0.1～0.2 μg/kg,and LOQs were 1.0～1.5 μ/kg and 0.2～0.4 μg/kg,respectively.The enrofloxacin matrix effect values in chicken tissues and pork ranged from-15.44%～-12.02%,and the ofloxacin matrix effect values ranged from-13.79%～11.08%,with weak matrix effects in all four matrices.The enrofloxacin matrix effect values in chicken whole eggs,egg albumens,and egg yolks ranged from-10.99%～-6.49%,and the matrix effect values of ofloxacin ranged from-7.79%～-5.66%,with weak matrix effects presenting in all three matrices.The method was validated to meet the requirements of the Chinese Ministry of Agriculture and Rural Affairs NY/T 1896-2010 standard for the detection of veterinary drug residues.Moreover,the method has been successfully applied to the detection of actual samples to satisfy the technical requirements of various laboratories. |
