Abstract
The UV and visible absorption characteristics of thiamine hydrochloride, riboflavin and ascorbic acid have been studied in the pH range 1.0-11.0 in relation to the photochemical interaction of thiamine hydrochloride/ascorbic acid with riboflavin due to overlapping of their absorption bands in the UV region. The spectral variations in thiamine hydrochloride and ascorbic acid solutions on photolysis in the presence and absence of riboflavin have been monitored and the effect of pH on the nature of these variations has been discussed. A comparison of the magnitude of spectral variations in the presence and absence of riboflavin indicates that the photolysis of thiamine hydrochloride is inhibited by riboflavin whereas that of ascorbic acid is promoted by riboflavin. The non-ionised forms of thiamine hydrochloride and ascorbic acid appear to be less susceptible to photolysis than the ionised forms. Thiamine hydrochloride and ascorbic acid are more stable to photodegradation in the acid range in the presence and absence of riboflavin.