Multiresidue HPLC analysis of ten quinollones in milk after solid phase extraction: Validation according to the European Union Decision 2002/657/EC

A rapid and sensitive analytical method was developed for the residue analysis of ten quinolones (enoxacin (ENO), ofloxacin (OFL), norfloxacin (NOR), ciprofloxacin (CIP), danofloxacin (DAN), enrofloxacin (ENR), sarafloxacin (SAR), oxolinic acid (OXO), nalidixic acid (NAL), and flumequine (FLU)) in cow's milk. The analytes were extracted from milk by a deproteinization step followed by a simple SPE cleanup procedure using LiChrolut RP-18 Merck cartridges. Recoveries varied between 75 and 92%. HPLC separation was performed at 25 degrees C using an ODS-3 PerfectSil((R)) Target (250 x 4 mm(2)) 5 mu m analytical column (MZ-Analysentechnik, Germany). The mobile phase consisted of a mixture of TEA 0.1 % - CH3CN - CH3OH, delivered by a gradient program at the flow rate of 1.2 mL/min. Elution of the ten analytes and the internal standard (caffeine, 7.5 ng/mu L) was completed within 27 min. Column effluent was monitored using a photodiode array detector, set at 275 and 255 nm. The developed method was validated according to the criteria of Commission Decision 2002/657/ EC. The LODs of the specific method of quinolones' determination in milk varied between 1.5 and 6.8 ng/mu L.