In pH 4.5～6.5 Britton-Robinson buffer media, fluoroquinolone antibiotics (FLQs) such as ciprofloxacin (CIP), norfloxacin (NOR), ofloxacin (OF), and levofloxacin (LEV) were reacted with Co^2＋ to form chelated cations, which further bound with Congo Red to form the ion association complexes, resulting in the great enhancement of resonance Rayleigh scattering (RRS). The four FLQs reaction products have similar spectral characteristics and their maximum RRS wavelengths are all located at 560 nm, and there are two smaller RRS peaks at 382 and 278 nm. The linear ranges and the detection limits of the four FLQs are 0.026～2.64 μg•mL^－1 and 7.68 ng•mL^－1 for CIP, 0.045～3.20 μg•mL^－1 and 13.00 ng•mL^－1 for NOR, 0.037～4.00 μg•mL^－1 and 11.24 ng•mL^－1 for OF, 0.039～4.00 μg•mL^－1 and 11.80 ng•mL^－1 for LEV, respectively. A simple, rapid and sensitive RRS method for the determination of FLQs in pharmaceutical formulation and human urine samples was developed. The reaction mechanism has been also investigated.

Key words: fluoroquinolone antibiotics, Co^2＋, Congo red, resonance Rayleigh scattering