Ascorbic acid degradation in aqueous solution during UV-Vis irradiation.

This work studied the effect of multi-wavelength UV processing on the ascorbic acid content of aqueous solutions, at different pH values (3, 4, and 5). The source of radiation was a mid-pressure mercury lamp (460 W), emitting between 250 and 740 nm. The samples were treated for 60 min, at 25 °C and 45 °C, with the lamp on and with the lamp off. A radiation balance was performed to estimate the total radiation power absorbed by the whole solution. Ascorbic acid content was reduced, either in irradiated or non-irradiated solutions, due to aerobic oxidation. But, in most cases, irradiation did not accelerate degradation. This can be explained by the fact that ascorbic acid barley absorbs ultraviolet in the interval of wavelengths emitted by the lamp (only 31% of the incident radiation P(0) could be absorbed by the solutions). Therefore, mid-pressure mercury lamps are helpful to avoid Vitamin C photo-degradation.