Effect of light intensity and wavelengths on photodegradation reactions of riboflavin in aqueous solution.

A study of the effect of light intensity and wavelengths on photodegradation reactions of riboflavin (RF) solutions in the presence of phosphate buffer using three UV and visible radiation sources has been made. The rates and magnitude of the two major photodegradation reactions of riboflavin in phosphate buffer (i.e., photoaddition and photoreduction) depend on light intensity as well as the wavelengths of irradiation. Photoaddition is facilitated by UV radiation and yields cyclodehydroriboflavin (CDRF) whereas photoreduction results from normal photolysis yielding lumichrome (LC) and lumiflavin (LF). The ratios of the photoproducts of the two reactions at 2.0 M phosphate concentration, CDRF/RF (0.09-0.22) and CDRF/LC (0.54-1.75), vary with the radiation source and are higher with UV radiation than those of the visible radiation. On the contrary, the ratios of LF/LC (0.15-0.25) increase on changing the radiation source from UV to visible. The rate is much faster with UV radiation causing 25% degradation of a 10(-5) M riboflavin solution in 7.5 min compared to that of visible radiations in 150-330 min.