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Sensitive Bromatometric Determination Of Finasteride In Pharmaceuticals Based On Complex-Formation Reactions

K.Basavaiah, B.C.Somashekar, U.R.Anilkumar, V. Ramakrishna

Two highly sensitive spectrophotometric methods are described for the determination of finasteride in pure form and tablet form. The methods are based on the bromination of finasteride by a measured excess of insitu generated bromine followed by the determination of residual bromine by two different redox-complexation reaction schemes. In one procedure (method A), the residual bromine is treated with an excess of iron (II) and the resulting iron (III) is complexed with thiocyanate and measured at 470 nm. The second approach (method B) involves treating the unreacted bromine with a calculated and known excess amount of iron (II) and complexing the remaining iron(II) with orthophenanthroline at a raised pH followed by measurement at 510 nm. In both methods, the amount of bromine reacted corresponds to the amount of finasteride. In method A, the absorbance is found to decrease linearly with increasing concentration of finasteride (r = -0.9997) whereas a linear increase in absorbance (r = 0.9999) resulted in method B. The systems obey Beer’s law for 0.5-4.0 and 0.5-6.25 μg/ ml for method A and method B, respectively. The calculated apparent molar absorptivity values are 9.94×104 and 6.68×104 l mol/ cm for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.0038 and 0.0056 μg/cm2. The limits of detection (LOD) and quantification (LOQ) are also reported for both methods. Accuracy, and intra-day and inter-day precision of the methods were established as per the present ICH guidelines. The proposed methods were applied successfully to the determination of finasteride in tablets and the results were found to agree closely with the label claim. The results were also compared statistically with those obtained by a reference method by applying the Student’s t-test and Ftest. The excipients did not interfere in the determination. The accuracy of the methods were further confirmed by performing recovery tests via standard addition method.