Kinetic spectrophotometric determination of ascorbic acid

A simple, rapid kinetic spectrophotometric method was developed for the quantitative estimation of ascorbic acid. The method is based on in situ oxidation of quercetin with N-bromosuccinimide into a red colored compound which was measured at 515 nm. The rate of the reaction was followed by measuring the decrease in absorption intensity of oxidized quercetin as a result of its reduction by ascorbic acid. Ascorbic acid in the range of 2-25 micrograms/ml was determined using slope and fixed time methods. In addition, the variable time method allowed the determination of 5-25 micrograms/ml of ascorbic acid. Interference from frequently encountered excipients, additives, some amino acids and minerals was studied. The method was applied for determination of ascorbic acid in some pharmaceutical preparations with average recovery of 98.52% and RSD not exceed 3.52%.