High-performance liquid chromatographic determination of ciprofloxacin in plasma samples.

A new bioanalytical high-performance liquid chromatographic (HPLC) method for the determination of ciprofloxacin with norfloxacin as an internal standard was developed and validated for plasma samples. Norfloxacin is structural homologue of ciprofloxacin and exhibits similar retention properties. The quality of respective peak separation is strongly influenced by amphoteric character of ciprofloxacin and norfloxacin as well. In previously published HPLC methods on conventional C18 reversed-phase [F. Belal, A.A. Al-Majed, A.M. Al-Obaid, Talanta 50 (1999) 765-786; G. Carlucci, J. Chromatogr. A 812 (1998) 343-367], ion pair reagents were added into the mobile phase to suppress peak tailing. In comparison with endcapped and high purity silica reversed-phase sorbent (Purospher RP-18e, Merck), which yielded symmetrical peaks, separation efficiency was further enhanced in our method. Gradient elution mode using acetonitrile and phosphate buffer pH 3 on the pentafluorophenylpropyl stationary phase (250-4.6 mm Discovery HS F5, 5 microm, Supelco) was carried out. The resolution of 4.1 for ciprofloxacin-norfloxacin peaks was achieved. Sample preparation by SPE C18 (Supelclean) with recovery 72% was performed. Fluorescence detection with lambda(excit)=280 nm, lambda(emis)=446 nm was used. After the validation, the bioanalytical HPLC method was applied to pharmacokinetic studies.