Stability-indicating methods for determining omeprazole and octylonium bromide in the presence of their degradation products

Four stability-indicating assays were developed for determining omeprazole and octylonium bromide. Omeprazole is photodegraded and estimated in the pr esence of its degradation products sulphenamide (I) and benzimidazole sulph ide (II) by 2 methods. The first method depends on use of first-, second-, and third-derivative spectrophotometry at 290.4, 320.6, and 311.6 nm, respe ctively. The second method is based on applying the charge-transfer techniq ue with chloranil as pi acceptor to form a complex with omeprazole, the abs orbance of which is measured at 377 nm, These methods determine omeprazole in concentration ranges of 5-20 mu g/mL by first-, second-, and third-deriv ative spectrophotometry and 10-50 mu g/mL by charge-transfer complexation w ith mean accuracies of 99.92 +/- 0.73, 99.71 +/- 1.02, 99.64 +/- 0.66, and 100.24 +/- 0.81%, respectively. Octylonium bromide is determined by a densi tometric method using thin-layer chromatography in the presence of its degr adation products p-[2-(n-octyoxy)benzoyl]-aminobenzoic acid (III) and dieth yl-(2-hydroxyethyl)methyl ammonium bromide (IV) without any interferences. Alternatively, octylonium bromide is evaluated by a colorimetric method usi ng the acid dye rose bengal, The ion pair formed is extracted in chloroform at pH 4, and its absorbance is measured at 562 nm, These methods determine octylonium bromide in the presence of its degradation products in concentr ation ranges of 0.1-0.5 mu g/mu L by densitometry and 4.5-22.5 mu g/mL by c olorimetry, with mean accuracies of 100.21 +/- 0.93 and 99.73 +/- 0.89%, re spectively, The suggested methods were used to determine drugs in bulk powd er, laboratory-prepared mixtures, and pharmaceutical dosage forms. Results were compared statistically with those obtained with reference methods.