Spectrophotometric Determination of Vitamin C in Pharmaceutical Preparations Using Ammonium Metavanadate

A rapid, and accurate direct spectrophotometric method was developed for the determination of vitamin C in pharmaceutical preparations using ammonium metavanadate as a reagent. This method is based on formation of green colored complex between vitamin C and ammonium metavanadate. The optimum conditions for the determination of vitamin C were established. The maximum absorbance of complex was obtained at 395 nm. Under the optimum conditions, a calibration graph was obtained and a linear relationship between absorbance and analyte concentration was found between 40-320 μg/cm³. The molar absorptivity was found to be 9.0 x 10^-4 dm³ mol⁻¹ cm⁻¹. The coloured complex in the extract was found to be stable for 4 hours. The different parameters such as effect of pH, reagent concentration and accuracy and precision were studied .The proposed method was successfully applied to determination of vitamin C in pharmaceutical preparations such as Amla squash (Nutri value), Orange peel powder, and Astymin drops C. The effect of foreign ions causing interference that are commonly found with L-ascorbic acid in the samples analyzed were studied by adding different amounts of those species to a solution containing 80.00 μg/cm³ of ascorbic acid. Many of the ingredients commonly found in these formulations did not interfere. The results obtained with the proposed method showed good agreement with those calculated by using known reference method pH metric titration.