Photochemical interaction of ascorbic acid with riboflavin, nicotinamide and alpha‐tocopherol in cream formulations

Abstract

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.

Factors affecting formulation characteristics and stability of ascorbic acid in water‐in‐oil creams

“…The iodimetric method has previously been applied to the analysis of o/w creams of AA by Ahmad et al . . However, in this study, the method has been applied to w/o creams and, therefore, it was validated prior to analysis in the presence of all excipients including stabilizer and degradation products.…”

“…On the basis of the various cream formulations reported in the literature , the following basic formula was used for the preparation of w/o creams containing AA:…”

“… and Ahmed et al . . The method was slightly modified and involved the extraction of AA with methanol‐acetone mixture; 1 : 1, v/v (3 × 10 mL), followed by pH adjustment to 2.0 with H 3 PO 4 .…”

“…AA is relatively more stable in dry form as compared with its aqueous solution . Its degradation is affected by a number of factors including oxygen, temperature, humidity, pH, light and formulation ingredients .…”

Photo, thermal and chemical degradation of riboflavin

“…Similarly, a 86% reduction in the formation of 2,3-butanedione was observed in RF solution when the concentration of sodium azide was increased from 0 to 5.0 mM [59]. A photochemical interaction between ascorbic acid and RF has also been studied in oil-in-water creams when irradiated with UV light [127]. Various other quenchers have been used to deactivate the excited states of RF such as β-carotene and lycopene [128], glutathione, D-mannitol [129], phenol [80], polyphenols such as catechin, epigallocatechin, and rutin [70], potassium iodide [81,129], purine derivatives such as uric acid, xanthine, hypoxanthine [130], α-, β-, γ- and δ-tocopherols [128], vitamin B 6 family [131], xanthone derivatives [132], and 1,4-diazabicyclo[2,2,2]octane and 2,5-dimethylfuran [133].…”