Abstract
A new multi-residue analytical method for simultaneous determination of four antibiotic residues (doxycycline (DOX), enrofloxacin (EN), ciprofloxacin (CP) chloramphenicol (CAM) in cow's milk has developed and validated by liquid chromatography-tandem mass spectrometry, was successfully applied to investigate commercially available cow's milk in Jordan. The analytes including etoricoxib as IS were extracted using liquid-liquid extraction and separated from their matrix chromatographically by using Fortis UniverSil Cyano column (50 x 2.1 mm, 5 mu m), eluted by a mobile phase of 0.5 mM ammonium chloride/methanol/formic acid (35 : 65 : 0.08%, v/v) and delivered isocratically at a constant flow rate of 0.4 mL/min for total LC run time of 1 min. Twenty-six cow's milk samples from different brands of dry powder milk, long shelf-life milk, and raw untreated milk were collected randomly from the Jordanian market and analyzed in the triplicate analysis. The calibration curve was linear within the dynamic range of 10-1000 ng/mL in spiked milk for each analyte and the correlation coefficients were greater than 0.9973 for all calibration curves during validation. The internal standard-normalized matrix effects extend from 0.901 to 1.11. The intra-assay and inter-assay precision normalized matrix effects extend from 0.901 to 1.11. The within-day and between-day precision ranged from 2.60-12.71% and 2.68-12.66%, respectively, and the relative error of accuracy does not exceed 15%. The results obtained are less than the approved stated regulatory guidelines and all samples screened were found to be free of any of the antibiotics tested.