SPECTROPHOTOMETRIC DETERMINATION OF L-ASCORBIC ACID USING POTASSIUM THIOCYANATE AS A STABILIZER

A rapid, sensitive and accurate direct spectrophotometric method was developed for the determination of L-ascorbic acid in pharmaceutical preparations. Potassium thiocyanate (0.02 M) in phosphate buffer was used to stabilize ascorbic acid in aqueous solutions. The molar absorptivity of the proposed method was found to be 1.42 x 10(4) dm(3) mol(-1) at 266 nm. Beer's law was obeyed in the concentration range of 0.25 - 12.0 mu g/cm(3) for L-ascorbic acid. The detection limit was 0.075 mu g/cm(3) and the relative standard deviation 0.73 % for a concentration of 8.00 mu g/cm(3) of L-ascorbic acid (n = 7). Many of the ingredients commonly found in vitamin C products do not interfere. The proposed method was successfully applied to assays of L-ascorbic acid in pharmaceutical preparations. The results obtained with the proposed method showed good agreement with those given by the titrimetric method using iodine.