A study on the oxidation kinetics of ascorbic acid mediated by methylene blue

A redox-driven reversible color tuning technique has been successfully used to investigate the oxidation kinetics of ascorbic acid (AA) and the effects of MB under O2-rich conditions. The blue MB is first reduced to form colorless leucomethylene (LMB) by adding AA, in which LMB is subsequently oxidized to recover MB by injecting O2, and AA is simultaneously monitored by characteristic absorption peaks of MB at 664 nm. It is found that the zero-order oxidation reaction of AA has rate constants of 0.193 mol L1 s1 under oxygen-saturated atmospheres. MB not only is a good spectral probe, but also leads to a 35.5% decrease in the activation energy barrier and a 1.5-fold increase in the rate constant for the oxidation reaction of AA. Moreover, the proposed approach is applied to the determination and oxidation evaluation of AA in tablet dosage forms, showing the relative standard deviation (RSD) of 2.1%, and the merits of low cost, high sensitivity and good reproducibility.