Kinetic spectrophotometric determination of ascorbic acid in pharmaceutical formulations

Sensitive, simple and fast kinetic spectrophotometric method for determination of ascorbic acid has been described. The procedure is based on reduction of iron(III) to iron(II) by ascorbic acid and formation of a complex between iron(II) and 2,2'-bipyridine. Reaction rate was monitored spectrophotometrically by measuring the increase in absorbance of the formed complex at 522 nm. Ascorbic acid was determined using a fixed-time (3 min) method in two concentration ranges: 0.1-15 mg nL - 1 and 20-45 mg mL - 1 ; the corresponding correlation coefficients were 0.998 and 0.999, respectively. Relative standard deviation for 10 replicate determinations of ascorbic acid in 2 mg mL - 1 solution was 0.47% and detection limit equalled 0.032 μg mL - 1 . The proposed method was successfully applied to the determination of ascorbic acid in pharmaceutical formulations. Reliability of determination was confirmed applying standard iodimetric method.