Multi-residue determination of seven quinolones antibiotics in gilthead seabream using liquid chromatography–tandem mass spectrometry

A sensitive and selective confirmatory analytical method for the multi-residue determination of seven quinolones (ciprofloxacin, enrofloxacin, sarafloxacin, danofloxacin, oxolinic acid, nalidixic acid and flumequine) in gilthead seabream (Sparus aurata) was developed. The sample pre-treatment involves extraction with 0.1 M NaOH and purification by solid-phase extraction (SPE) on Waters Oasis HLB cartridges followed by the determination of all compounds in a single LC–electrospray ionization MS/MS run. Separation was achieved on a Perfectsil ODS-2, 5 μm, 250 mm × 4 mm, analytical column (MZ Analysentechnik) by gradient elution using a mixture of 0.2% (v/v) formic acid, methanol and acetonitrile within 30 min. Multiple reaction monitoring (MRM) was used for selective detection of each quinolone. Accuracy was evaluated through recovery studies at three different fortification levels. The mean recoveries are between 90 and 132% for the selected levels with RSD values lower than 20%. The method presents satisfactory results for linearity, precision and limits of quantification. The latter are much lower than the maximum residue limits (MRLs) established by the European Union for quinolones in fish tissues (6–8 μg/kg).