Bromatomatric assay of gatifloxacin in pharmaceuticals

Abstract

Three new, simple, and cost-effective visible spectrophotometric methods are proposed for determination of gatifloxacin (GTF) using bromate-bromide mixture, and three dyes, methyl orange, indigocarmine and thymol blue, as reagents. The methods engross the addition of a known excess of bromate-bromide mixture to GTF in hydrochloric acid medium followed by determination of residual bromine by reacting with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (method A) or indigo carmine and measuring the absorbance at 610 nm (method B) or thymol blue and measuring the absorbance at 550 nm (method C). In all the methods, the amount of bromine reacted corresponds to the amount of GTF, and the absorbance is found to increase linearly with the concentration of GTF. Under the optimum conditions, GTF could be assayed in the concentration range 0.25-1.5, 0.5-6.0, and 0.5-10 mg/mL by method A, method B and method C, respectively. The apparent molar absorptivities are calculated to be 1.6x105, 4.0x104 and 3.2x104 L mol-1 cm-1 for the method A, method B and method C, respectively, and the corresponding Sandell sensitivity values are 0.0025, 0.010 and 0.012 ?g/cm2. The intra-day and inter-day precision, and the accuracy of the methods were evaluated as per the current ICH guidelines. The methods were successfully applied to the determination of GTF in pharmaceutical preparations without the interference from any of the pharmaceutical adjuvant.