Analysis of polymeric quaternary ammonium salts as found in cosmetics by metachromatic polyelectrolyte titration

Abstract

Metachromatic polyelectrolyte titration was investigated as a means of analyzing polymeric quaternary ammonium salts (polyquaterniums) of relatively low charge density used as ingredients in cosmetics. They are of possible toxicological concern, but little is known of their environmental fate and behavior. With o-toluidine blue as the indicator, determination of the concentration of a range of polyquaterniums of commercial importance and cosmetic origin was possible. Using a visual endpoint, normalities as low as 3 × 10−5 N could be determined, while with a spectrophotometric endpoint, the technique was effective to approximately 3 × 10−6 N. The concentrations (g L−1) to which these normalities correspond depend on the charge density of the polymer. Polyquaterniums are frequently used in association with anionic surfactants in cosmetic formulations and the presence of an anionic surfactant even in excess did not affect results although the color change was less stable. Titration in the presence of prepared humic acid was also possible.