Spectrophotometric determination of enrofloxacin through the formation of a binary complex with iron III, ion-pair and charge-transfer complexation in pure and dosage forms

Three simple and accurate spectrophotometric methods are described for the determination of enrofloxacin, a new fluoroquinolone synthetic orally active broad spectrum antibacterial. The first method is based on the reaction with iron III forming a water soluble yellow complex with maximum absorbance at 434 nm. The method allows the determination of 25-140 mu gml(-1). The second method involves ion-pair formation with bromocresol purple (BCP) in presence of phthalate buffer (pH 4.8+/-0.4). The yellow ion-pair is extracted with chloroform and the absorbance is measured at 410 nm. The method allows the determination of 4-18 mu gml(-1). The third method is based on the reaction of the. drug with 8-dichloro-5,6 dicyano-p-benzoquinone (DDQ) in methanol as pi-acceptor to give a molecular charge-transfer complex, with maximum absorbance at 460 nm. The method permits the determination of 50-240 mu gml(-1). Optimization of different experimental conditions were described. Beer's law was obeyed for the three methods and the relative standard deviation was found to be less than 2%. The methods have been applied successfully to the analysis of commercially available enrofloxacin preparations without interference from the ingredient commonly found.