Novel selective kinetic spectrophotometric method for determination of norfloxacin in its pharmaceutical formulations

Novel selective and simple kinetic spectrophotometric method has been developed and validated for the determination of norfloxacin (NOR) in its pharmaceutical formulations. The method was based on the reaction of N-vinylpiprazine formed from the interaction of the mono-substituted piprazinyl group in NOR and acetaldehyde with 2,3,5,6-tetrachloro-1,4-benzoquinone to give colored N-vinylpiprazino-substituted benzoquinone derivative. The formation of the colored product was monitored spectrophotometrically by measuring the absorbance at 625 nm. The factors affecting the reaction was studied and optimized. The stoichiometry of the reaction was determined and the reaction pathway was postulated. The activation energy of the reaction was calculated and found to be 5.072 kJ mol−1. The initial rate and fixed time (at 5 min) methods were utilized for constructing the calibration graphs. The graphs were linear in concentration ranges of 20–150 and 10–180 μg mL−1 with limits of detection of 8.4 and 3.2 μg mL−1 for the initial rate and fixed time methods, respectively. The analytical performance of both methods was fully validated, and the results were satisfactory. No interferences were observed from the excipients that are commonly present in the pharmaceutical formulations, as well as from tinidazole that is co-formulated with NOR in some of its formulations. The proposed methods were successfully applied to the determination of NOR in its commercial pharmaceutical formulations. The label claim percentages were 98.4–100.4 ± 0.52–1.04%. Statistical comparison of the results with those of the official method showed excellent agreement and proved that there was no significant difference in the accuracy and precision between the official and the proposed methods.