Characterization of dehydroascorbic acid solutions by liquid chromatography/mass spectrometry

The composition of a commercial dehydroascorbic acid (DA) solution at pH 2 was investigated by liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) to establish the nature of its different forms and its decomposition products. In freshly prepared solutions, dimeric forms of DA and the hydrated bicyclic hemiketal of DA are the species mainly present in solution. In the presence of light, the initial dimeric species disappears over time to give other dehydrated dimers some of which decompose to the monomer. The comparison of these data with similar data obtained for ascorbic acid (AA) solutions under the same experimental conditions revealed that, in the presence of light, the aging of such AA solutions gives rise to only the hemiketal form of DA, and that no dimeric species of DA were formed. The presence of the hemiketal form of DA was not revealed by analysis of the same AA solutions using the conventional LC/UV technique. The natural form of DA from the oxidation of AA is the hydrated bicyclic form.