spectrophotometric determination of l-ascorbic acid in pharmaceuticals based on its oxidation by potassium peroxymonosulfate and hydrogen peroxide

Two new, accurate, precise, and sensitive spectrophotometric methods were developed for the assay of L-ascorbic acid in pharmaceutical preparations. The determination of L-ascorbic acid was based on its oxidation by potassium peroxymonosulfate (method A) and hydrogen peroxide in the presence of Cu(II) as a catalyst (method B). The molar absorptivities were found to be 1.48×104 and 1.06×104 L mol–1 cm–1 for methods A and B, respectively. Beer's law was obeyed in the concentration range of 0.65–11.20 μg mL–1 for method A and 0.51–16.00 μg mL–1 for method B. Other compounds commonly found in vitamin C and multivitamin products did not interfere with the determination of L-ascorbic acid.. The proposed methods were successfully applied for the determination of L-ascorbic acid in pharmaceutical formulations. The results obtained with the proposed methods showed good agreement with those given by the titrimetric method using iodine.