A SPECTROSCOPIC METHOD FOR THE EVALUATION OF THE SUBSTANTIVITY OF N-LAUROYL SARCOSINATE TO HUMAN SKIN

Substantivity is an important property of ingredients in cosmetic form ulations. This paper describes a novel analytical technique for the st udy of adsorption of sarcosinate surfactants on live human skin. The p erdeutero analogue of lauroyl sarcosinate was chosen as the model for the surfactant. The skin after contact with the deutero surfactant was rinsed and examined by ATR-infrared spectroscopy. The presence of spe ctral bands at frequencies characteristic of C-D bonds provides eviden ce for the adsorption of the surfactant on skin. It is shown that the surfactant adsorbs at 10-mu g/cm(2) levels and that the pH of the surf actant solution has a significant impact on its substantivity. The ana lytical method described in this paper may be useful for the investiga tion of the sorption of other materials on skin and other substrates.