Photodegradation of vitamine B2

The investigation on the influence of light on riboflavine was studied by following its polarographic behaviour as a function of the time. Measurements of DP 50 were performed at 3 different pH 3.5; 6.5 and 8.5 in suitable buffer solutions by using 1.00 mol dm-3 NaCl or N(CH3)4Cl as support electrolyte, in the absence and in the presence of direct light. Polarograms carried out on solutions containing only crystalized riboflavine provided only one peak. The peak potential shifts to more negative potential by increasing pH. At pH = 8.5, polarograms, carried out on the same solutions under the direct light, showed decreasing of the peak corresponding to riboflavine and the formation of a new peak increasing as a function of the time of exposition to light. The trend of UV-visible spectra was followed by putting riboflavine on the direct light, but none change was observed. By comparing spectra of riboflavine and of lumiflavine, it was observed a good superimposition. At the same way, polarograms of lumiflavine showed the same behaviour of riboflavine. By taking in mind that lumiflavine is the degradation product of riboflavine, but with the alone difference of the elimination of the ribose chain, it was possible explain that the electroactive groups of riboflavine and lumiflavine were the same and also the groups responsible of the absorption in the spectra were the same. The ligth degradation of riboflavine and lumiflavine gave lumichrom. The cinetic of transformation could be well approximated with a first order reaction.