Reversed-phase ion-pair high-performance liquid chromatographic determination of fluoroquinolones in human plasma

A simple and sensitive method is described for the determination of fluoroquinolones by HPLC on a C-18 column using fluorescence detection. Using a mobile phase of 25% (v/v) acetonitrile phosphate buffer (pH 2.0), adequate retention and separation among the solutes norfloxacin, amifloxacin, enoxacin, and pipemidic acid have been obtained using sodium lauryl sulphate as the pairing ion and tetrabutylammonium bromide as the counter ion. The chromatographic conditions selected have been used for the quantitation of norfloxacin, amifloxacin, and enoxacin in human plasma using pipemidic acid as the internal standard. A simple single-step protein precipitation procedure has been employed for pretreatment of plasma samples. The detection limits of the assay for enoxacin, amifloxacin, and norfloxacin are approximately 100, approximately 10, and approximately 20 ng/mL, respectively. The method has been employed for the determination of amifloxacin in plasma samples from a healthy volunteer following oral administration of a 400-mg amifloxacin capsule.