The effect of oxygen on the two separate one-electron reactions involved in the oxidation of ascorbic acid
was investigated. The rate of ascorbate radical (Asc) formation (and stability) was strongly dependent
on the presence of oxygen. A product of ascorbic acid oxidation was measurable levels of hydrogen peroxide,
as high as 32.5 lM from 100 lM ascorbic acid. Evidence for a feedback mechanism where hydrogen
peroxide generated during the oxidation of ascorbic acid accelerates further oxidation of ascorbic
acid is also presented.
The second one-electron oxidation reaction of ascorbic acid leading to the disappearance of Asc was
also strongly inhibited in samples flushed with argon. In the range of 0.05–1.2 mM ascorbic acid, maximum
levels of measurable hydrogen peroxide were achieved with an initial concentration of 0.2 mM
ascorbic acid. Hydrogen peroxide generation was greatly diminished at ascorbic acid levels of 0.8 mM
or above.