Multi-residue determination of veterinary drugs in cheese by QuEChERS and liquid chromatography-tandem mass spectrometry

A rapid and sensitive method has been developed for the simultaneous determination of 50 veterinary drugs (including macrolides, quinolones, sulfonamides, and tetracyclines) in cheese using a modified QuEChERS method coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). After adding Na(2)EDTA buffer solution and ceramic homogenizer, the cheese sample was extracted by 5% (v/v) acetic acid. acetonitrile, sodium chloride and anhydrous sodium sulfate were used for salting-out process. The resulting supernatant solution was purified by C-18 sorbent and the re-dissolved solution was analyzed by LC-MS/MS under dynamic multi. reaction monitoring (dynamic MRM) mode via positive electrospray ionization with a ZORBAX-SB-C-18 column. The limits of quantification (LOQ, S/N = 10) of the target compounds ranged from 0.05 mu g/kg to 20 mu g/kg in cheese. At spiked levels of 20, 50, 100 mu g/kg (n = 6), the percentages of drug with a recovery between 70% and 120% were 94%, 92%, and 96%, respectively. The relative standard deviations (RSDs) were between 1% and 14%. This method has been applied to determine seven real samples from markets. Roxithromycin and flumequine have been detected in two samples separately. The results demonstrated that this simple, rapid and accurate method is suitable for the detection of multi-class veterinary drugs in cheese.