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

A second-derivative spectrophotometric method ((2)D) and a derivative ratio spectrum zero crossing ((1)DD) 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 microg ml(-1) raubasine for the ((2)D) method and 12-24 microg ml(-1) almitrine dismesylate for the ((1)DD) 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 ((2)D) method and almitrine dismesylate with an accuracy of 99.98 +/- 0.602 (n = 7) for the ((1)DD) 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.