Stability‐indicating methods for the determination of a mixture of almitrine and raubasine by derivative spectrophotometry

A second‐derivative spectrophotometric method (²D) and a derivative ratio spectrum zero crossing (¹DD) method were used to determine raubasine and almitrine dismesylate in the presence of raubasine degradation product, using methanol as a solvent. Linear relationships were obtained in the range from 6–20 µg ml^?1 raubasine for the (²D) method and 12–24 µg ml^?1 almitrine dismesylate for the (¹DD) method. By applying these methods it was possible to determine raubasine in its pure powdered form with an accuracy of 99.93 ± 1.116 (n = 8) for the (²D) method and almitrine dismesylate with an accuracy of 99.98 ± 0.602 (n = 7) for the (¹DD) method. Laboratory‐prepared mixtures containing different ratios of raubasine, almitrine dismesylate and raubasine degradation product were analysed and the proposed methods were valid up to 50% of raubasine degradation product. They were found to be suitable stability‐indicating assay methods for raubasine and almitrine dismesylate in pharmaceutical formulations. Copyright © 2009 John Wiley & Sons, Ltd.