Moisture induced solid phase degradation of l-ascorbic acid part 2, separation and characterization of the major degradation products

The influence of moisture in the presence and absence of air on the solid state degradation of l-ascorbic acid has been investigated previously [1]. Reaction kinetics were studied using tristimulus colorimetry and a quantitative high performance liquid chromatographic assay for both total l-ascorbic acid and dehydroascorbic acid. The degradation gave rise to a discolouration of the samples, the most severely degraded samples were almost black in appearance although over 68% w/w of the l-ascorbic acid remained. The samples were analyzed for the presence of carbonyl compounds, furan related compounds, compounds responsible for the discolouration and evolution of carbon dioxide. No 2,4-dinitrophenylhydrazine (2,4-DNP) derivatives of carbonyl compounds or furan related compounds were detected by HPLC. An HPLC screening procedure was developed which was used to monitor for compounds responsible for the discolouration, at least eight unknown compounds were resolved and a relative response factor of 5.47 was assigned to them with respect to l-ascorbic acid at 280 nm. One mole of carbon dioxide was evolved per mole of l-ascorbic acid. This paper describes the investigation into the identity of the degradation products.