Spectrofluorimetric study of the acid–base equilibria and complexation behavior of the fluoroquinolone antibiotics ofloxacin, norfloxacin, ciprofloxacin and pefloxacin in aqueous solution

A spectrofluorimetric study of the acid–base properties and of the complexation behavior of the fluoroquinolone antibiotics ofloxacin (OF), norfloxacin (NOR), ciprofloxacin (CIP) and pefloxacin (PEF) has been performed. Their dissociation constants were determined by a combined potentiometric/fluorimetric technique. All studied fluoroquinolones form fluorescent complexes with Sc3+ in slightly acidic solutions (pH=4.2, λex∼280 nm, λem∼430 nm (480 nm for OF). A simple, rapid and sensitive spectrofluorimetric method based on the formation of scandium complexes has been developed for the determination of OF, NOR, CIP and PEF in aqueous solutions. Calibration graphs for all four fluoroquinolones were linear up to 1.0 μM, with results having a mean relative error of 3.2%. The 3σ detection limits are 1.1, 0.6, 0.5 and 1.0 nM for OF, NOR, CIP and PEF, respectively. The method has been successfully applied to the determination of NOR in synthetic serum samples (5.0–50.0 μM) after deproteinization with acetonitrile (serum–acetonitrile, 1 : 2 v/v) with a mean recovery of 93.4±1.1% (n=3).