Spectrophotometric Methods for Simultaneous Determination of Two Hypouricemic Drugs in their Combined Dosage Form

Abstract

Four simple, precise and accurate spectrophotometric methods have been developed for simultaneous determination of Allopurinol (ALP) and Benzbromarone (BENZ) in their bulk powder and pharmaceutical dosage form. Method (I) is dual wavelength analysis, method (II) is Q-analysis (graphical absorbance ratio) method, method (III) is the mean centering of ratio spectrophotometric (MCR) method while method (IV) is the extended ratio subtraction method (EXRSM). In method (I) two wavelengths were selected for each drug in such a way that the difference in absorbance was zero for the second drug. At wavelengths 238.2 and 261.2 nm ALP had equal absorbance values; therefore, these two wavelengths have been used to determine BENZ; on a similar basis 253 and 274.4 nm were selected to determine ALP. Method (II) involves the formation of Q-absorbance equation using the respective absorptivity values at 245.8 nm (isoabsorptive point) and 250 nm (λmax of ALP). In method (III) the absorption spectra of both ALP and BENZ with different concentrations were recorded over 210-280 and 210-275 nm, respectively, divided by the spectrum of suitable divisor of both ALP and BENZ and then they obtained ratio spectra were mean centered. Method (IV) starts with the normal ratio subtraction method (RSM) for determination of ALP at its λmax (250 nm), while an extension of the already developed method has been established as a new approach for BENZ determination at its λmax (238 nm). Accuracy, precision and recovery studies of the developed methods have been carried out in order to confirm their accuracy. Specificity of the methods was also tested by their application for determination of different synthetic mixtures and they have been successfully used for drugs determination in their combined dosage form. Statistical comparison of the developed methods with the reported HPLC one showed no significant difference.