Spectroscopic and tensiometric considerations on anionic surfactants (SDS) and ascorbic acid/ascorbates interactions

Abstract

The cosmetics and personal care products market is developing dynamically and the formulations of products are subject to numerous modifications due to consumer expectations and market trends. An increase in demand for products containing ascorbic acid or its more stable forms has been observed for several years. In this study, the correlation between SDS and ascorbic acid or its derivatives in aqueous solutions was assessed using spectroscopic and tensiometric methods. The influence of SDS interactions on the total antioxidant capacity of ascorbic acid/ascorbic acid derivatives was analyzed. The highest FRAP values of SDS-AA2G and SDS-EAC systems (0.17 and 2.71 mmol Fe2+/g, respectively) were at SDS concentration of 0.40 mM and were much higher than the ones of pure ascorbic acid derivatives. Based on the surface tension isotherms and Szyszkowski's equation, it was found that for the tested SDS/ascorbic acid, ascorbyl glucoside and 3-O-ethyl ascorbic acid systems, the CMC values were: 3.85, 2.54 and 3.31 mmol/dm3. There was also an influence on the values of the adsorption parameters, i.e. the surface excess at the saturated interface, the minimum molecular area in the adsorption layer at the saturated interface and the Gibbs free energy of adsorption. Moreover, in most of the analyzed cases, the tested systems had better wetting properties, which resulted in lower values of the contact angle than in the case of pure SDS solution.