Sensitive bromatometric assay methods for finasteride in pharmaceuticals

Three sensitive spectrophotometric methods are presented for the determination of finasteride in bulk and in tablets. The methods rely on the use of bromate-bromide reagent and three dyes namely, methyl orange, indigocarmine and thymol blue as reagents. They involve the addition of a measured excess of bromate-bromide reagent to finasteride in acid medium, and after the bromination reaction is judged to be complete, the unreacted bromine is determined by reacting with a fixed amount of either methylorange and measuring the absorbance at 520 nm (method A) or indigocarmine 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 insitu generated bromine reacted corresponds to the amount of finasteride. The absorbance measured at the respective wavelength is found increase linearly with the concentration of finasteride. Beer’s law is obeyed in the ranges 0.252.0, 0.5-6.0 and 1-12 μg mL-1 for method A, method B and method C, respectively. The calculated molar absorptivity values are 5.7x104, 3.12x104 and 1.77x104 L mol-1 cm-1 respectively, for method A, method B and method C, and the corresponding Sandell sensitivity values are 0.0065, 0.012 and 0.021 μg cm-2. The limits of detection (LOD) and quantification (LOQ) are also reported for all the methods. Accuracy and, intraday and inter-day precisions of the methods were established according to the current ICH guidelines. The methods were successfully applied to the determination of finasteride in commercially available tablets and the results were found to closely agree with the label claim. The results of the methods were statistically compared with those of a reference method by applying Student’s t-test and F-test. The accuracy and reliability of the methods were further confirmed by performing recovery tests via standard addition procedure.