Determination off four fluoroquinolones in milk by liquid chromatography

A liquid chromatographic (LC) method with fluorescence detection is presented for the analysis of 4 fluoroquinolones; enrofloxacin (ENRO), ciprofloxacin (CIPRO), sarafloxacin (SARA), and difloxacin (DIFLX) in milk. The procedure consists of extraction of milk with acidified ethanol, isolation and retention on a cation exchange solid-phase extraction column, elution with basic methanol, and LC analysis with fluorescence detection. LC analysis is performed by isocratic elution using an acetonitrile-2% acetic acid (15 + 85) mobile phase and an Inertsil phenyl column with fluorescence detection at excitation and emission wavelengths of 278 and 450 nm, respectively. A target level of 10 ppb for each of the 4 fluoroquinolones has been established for this method. Average recovery from fortified raw milk samples (5-100 ppb each) based on a 5-point standard curve calculation was 70-90%, with relative standard deviations of < 15%.