J AOAC Int. 1997 Sep-Oct;80(5):982-7.
Determination off four fluoroquinolones in milk by liquid chromatography.

Roybal JE, Pfenning AP, Turnipseed SB, Walker CC, Hurlbut JA.

U.S. Food and Drug Administration, Animal Drugs Research Center, Denver Federal Center, CO 80225-0087, USA.

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%.

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