The present work describes three visible spectrophotometric methods for the quantitative estimation of Manidipine in bulk and synthetic mixtures. Method A is based on the reaction of the drug with para-dimethylaminobenzaldehyde (PDAB) and methanolic sulfuric acid at room temperature to form a green chromogen measured at 436.97 nm. Method B is based on the reaction of the diazotized drug with N-napthylethylenediamine dihydrochloride (NEDD) to form a pink chromogen measured at 550.20 nm. Method C utilizes the reaction of manidipine with 3-methyl-2-benzothiazoniumhydrazone hydrochloride (MBTH) in the presence of ferric chloride to form a product measured at 480.21 nm. Under optimized reaction conditions, the proposed methods were validated as per ICH guidelines. Linearity was obeyed in the concentration ranges of 25125 μg/ml with the following linear regression equations for methods A, B, and C, respectively: Y = 0.002829 X + 0.01319, Y = 0.002325 X + 0.004275, Y = 0.0035 X + 0.001039. The limits of detection and limits of quantiÞ cation for methods A, B and C were 1.2024 and 1.212 µg/mL; 0.9798 and 3.6451 µg/mL, and 3.672 and 2.969 µg/mL respectively. Recovery studies were carried out by using the standard addition method and the results were found to be satisfactory. All methods have been applied successfully for the estimation of manidipine dihydrochloride in bulk and synthetic mixtures.
Key words: 3-Methyl-2-benzothiazonium hydrazone hydrochloride, manidipine dihydrochloride, N-napthyl ethylene diamine dihydrochloride, para-diaminobenzaldehyde, visible Spectrophotometry.