Simple and sensitive spectrophotometric assay of ofloxacin in pharmaceuticals based on ion-pair reaction

Abstract

Two simple, sensitive, economical and extraction-free spectrophotometric methods have been developed for the determination of ofloxacin (OFX) in pure form and in tablets. The methods are based on the interaction of OFX with two sulphonphthalein dyes, namely, bromothymol blue (method A) and bromophenol blue (method B) in dichloromethane medium to form stable, yellow-colored ion-pair complexes peaking at 410 nm. Under the optimum conditions, OFX could be assayed in the concentration ranges, 1.25-20 and 1.0-16 ?g mL-1 OFX by method A and method B, respectively, with correlation coefficient of 0.999 in both methods. The apparent molar absorptivity values are calculated to be 1.74 x 104 and 2.18 x 104, L moL-1 cm-1, for method A and method B, respectively, with corresponding Sandell sensitivity values of 0.021 and 0.017 ?g cm-2. The limits of detection (LOD) and quantification (LOQ) are also reported. The stoichiometry of the reaction was found to be 1:1 in both cases and the conditional stability constant (Kf) of the complexes have also been reported. The intra-day and inter-day variation was assessed. The methods were applied to determine OFX from marked tablet formulations. Statistical analysis proved that the proposed methods were both accurate and precise.