Stability of vitamin C (ascorbic acid) in tablets

Stability of ascorbic acid (vitamin C) in various tablet formulations and the nature and extent of formation of decomposition products (dehydroascorbic acid, diketogulonic acid, and oxalic acid) were determined under normal conditions of storage and in simulated use tests. IR spectrophotometric, colorimetric, fluorometric, titrimetric, polarographic, and chromatographic methods were applied. Recent implications concerning the instability of ascorbic acid in tablets and the potentially harmful nature of the breakdown products are shown to be unfounded. Under normal storage conditions, commerical-type ascorbic acid tablets are stable for over 5 years (greater than 95% potency retention). The amounts of all three breakdown products formed under the various storage conditions constitute a small percentage of the ascorbic acid content and pose no dietary hazard. IR spectroscopy was inadequate as a quantitative method for evaluating ascorbic acid potency in tablet formulations. The official titration methods and TLC, colorimetric, and polarographic determinations correlate well and define accurately the stability of ascorbic acid in these dosage forms.