In the present work a simple, accurate and precise method has been developed and validated for the simultaneous estimation of isosorbide di nitrate (ISD), hydralazine hydrochloride(HYD)in bulk and their combined dosage form by UV spectrophotometric methods. The method employes estimation of drugs by simultaneous equation method (SEM) using 208.28nm and 232nm i.e λmax values of ISD and HYD respectively. Method B employs the estimation of drugs by absorption correction method (ACM) at 232nm for HYD where absorbance of ISD is very low. Absorbance correction method was based on the property of additively of absorbance. At 232nm, Hydralazine hydrochoride showed absorbance while Isosorbide dinitrate showed very low absorbance. The method involved measurement of absorbance at wavelength 232 nm. For estimation of HYD, corrected absorbance was calculated at 208 nm due to the interference of HYD at this wavelength. Calibration curves were linear with correlation coefficient 0.999 over the concentration range of 2-10μg/mL and 2-10 μg/mL for ISD and HYD respectively. The percent recoveries of the drugs were found nearly 100 % representing the accuracy of the both methods. Validation of the proposed methods was carried out for its accuracy, precision, specificity, linearity and limit of detection according to ICH guidelines. The proposed methods can be successfully applied in routine work for the determination of isosorbide dinitrate and hydralazine hydrochloride in combined dosage form.
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