Estabilización de disoluciones acuosas de riboflavina por solapamiento espectral

the photostabilization of riboflavin (rf) in aqueous solution was evaluated through spectral overlap. previous studies established that wavelength at 445nm promoted rf degradation; hence dyes that exhibited high absorption performance at 445 nm were selected. the photoprotection study consisted in determining and comparing the rate constants (k0) of the rf photodegradation reactions in solutions (80 μm), both in presence and absence of dyes at different concentrations: tartrazine (40, 58, 71 y 187 μm), sunset yellow (80, 160, 442 y 1 600 μm) and quinoline yellow (80, 133, 160 y 1600 μm).the kinetics were estimated by irradiating the samples in a solar simulation chamber at 250 w×m-2 and at different times; then the residual rf was quantified by hplc method. the rate constants (k0) were determined by the integral method. when dyes are absent, the rf photodegradation is due to zero order kinetics (k0= 0.0012 mg×ml-1×min-1) with 79.9 % degradation after 20 min of exposure to light. when dyes are present, the rf stability improves significantly with increasing concentration of the dye; however, it was found that quinoline yellow at low concentrations (<160 μm) increased the ef degradation, whereas at the highest studied concentration, k0 was reduced 6 times, suggesting that chemical interactions occurred. most photoprotection was obtained from the sunset yellow at allowable concentration where rf concentration was unchanged after 30 min of irradiation. the study showed that the high photosensitizing capacity of riboflavin hindered the generic use of photoprotective technique through spectral overlapping, because physical-chemical effect of overlapping may be expected in addition to occurrence of photochemical interactions.