Spectrophotometric determination of ascorbic acid in pharmaceutical preparations

A spectrophotometric method is described for the determination of ascorbic acid based on its oxidation by iodate in acid medium in the presence of chloride ions. The ICI2- generated in this reaction is used to iodinate 2',7'- dichlorofluorescein dye. The red colour of the iodinated dye is measured at 525 nm. Several vitamins, sugars and metal ions do not interfere when present in amounts usually found in pharmaceutical preparations. The molar absorptivity at the colour system is 8.81 x 103 1 mol-1 cm-1 at 525 nm and Beer's law is obeyed in the range 0-300 μg of ascorbic acid. The procedure is simple, rapid and sensitive and suitable for routine determinations.