A simple and efficient LC/ESI/MS/MS method was developed to determine 18 (fluoro)quinolone (QNs) residues in milk,chicken, pork, fish and shrimp. This method is capable of screening and confirming the presence of 12 amphoteric QNs (marbofloxacin,norfloxacin, enrofloxacin, ciprofloxacin, desethylene ciprofloxacin, lomefloxacin, danofloxacin, sarfloxacin, difloxacin,ofloxacin, orbifloxacin and enoxacin) and 6 acidic QNs (oxolinic acid, nalidixic acid, flumequine, cinoxacin, piromidic acid and
pipemidic acid). The drugs were extracted from matrix with acetonitrile containing 1% formic acid, diluted in 10% acetonitrileand defatted by extraction with hexane. The LC separation was conducted on an XDB C-8 (150 mm × 4.6 mm, 5 μm) column with gradient elution of 20 mM ammonium formate in 0.1% formic acid-acetonitrile as the mobile phase. Mass spectrum acquisition was completed in the positive ion mode by applying multiple reaction mode (MRM). The decision limit (CCα) and detection capability(CCβ), stated in the Decision No. 2002/657/EC and the ISO standard No.11843, have been calculated in the case of nonauthorized
substance. The values of CCα ranged from 0.18 to 0.68 ng/g and CCβ ranged from 0.24 to 0.96 ng/g under specified conditions.