Photochemical interaction of ascorbic acid with riboflavin, nicotinamide and alpha-tocopherol in cream formulations.
The present work is based on a study of the effect of some vitamins such as riboflavin (RF), nicotinamide (NA) and alpha-tocopherol (TP) on the photodegradation of ascorbic acid (vitamin C) (AH₂) in oil-in-water cream formulations using a UV irradiation source. A UV spectrophotometric and the official iodimetric methods have been used for the assay of AH₂ in cream formulations. These methods have been validated in the presence of RF, NA and TP before their application to the creams. The recoveries of AH₂ in the creams are in the range of 90-95% and the reproducibility of the method is within ±5%. The apparent first-order rate constants (k(obs) ) for the photodegradation of AH₂ in the presence of RF, NA and TP, individually, in the creams have been obtained. The second-order rate constants for the photochemical interaction of AH₂ and the vitamins RF, NA and TP have been determined from the plots of k(obs) for AH₂ photolysis versus the individual vitamin concentration along with the values of k₀ from the intercept on the vertical axis. The values of k₀ in the presence of RF and NA are lower than those of the k(obs) , indicating that these vitamins act as photosensitizers for the degradation of AH₂ in creams. On the contrary, the value of k₀ in the presence of TP is higher than that of the k(obs) , suggesting a stabilizing effect of this vitamin on the degradation of AH₂ in creams. The mode of interaction of the individual vitamins with AH₂ on photolysis has been discussed.
Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi-74600, Pakistan.
I
I
Ahmad
M A
MA
Sheraz
S
S
Ahmed
R
R
Bano
F H M
FH
Vaid
D000287:Administration, Topical; D001205:Ascorbic Acid / Q000737:chemistry*; D002855:Chromatography, Thin Layer; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009536:Niacinamide / Q000737:chemistry*; D010777:Photochemistry; D012256:Riboflavin / Q000737:chemistry*; D024502:alpha-Tocopherol / Q000737:chemistry*
D009536:Niacinamide; D024502:alpha-Tocopherol; D001205:Ascorbic Acid; D012256:Riboflavin