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j. Soc. Cosmet. Chem., 43, 259-273 (September/October 1992) Assessment of the substantivity of cationic quaternary compounds to hair by potentiometric titration using the surfactant electrode NGHI VAN NGUYEN, DAVID W. CANNELL, ROGER A. MATHEWS, and HANS H. Y. OEI, Redken Laboratories Inc., Research and Development Department, 6625 Variel Avenue, Canoga Park, CA 91303. Received February 7, 1992. Synopsis A new method to measure the sorption of cationic quaternary compounds by hair is reported. The method employs the potentiometric titration of cationic compounds, using a surfactant electrode as an endpoint indicator. Cationic uptake was determined from the difference of the cationic content in the solutions before and after the treatment of hair. By this method, the substantivity to bleached hair of mono- and poly- functional quaternary ammonium conditioning agents, as well as animal and botanical quaternary ammo- nium proteins, was measured as laurdimonium hydrolyzed wheat protein quaternium-26 stearalko- nium chloride cocodimonium hydrolyzed keratin protein. The results are consistent with previously published accounts: cationic uptake of quaternary compounds increases with increased solution concentra- tion, treatment time, temperature, and hair damage. INTRODUCTION Quaternary ammonium compounds have been widely used as hair conditioning agents in cosmetics. These compounds encompass cationic surfactants, cationic polyelectrolytes (polyquaternary polymers, copolymers), and cationic quaternary derivatives of hydro- lyzed proteins (animal, botanical). Deposition (substantivity) of these cationic com- pounds on hair can produce effects on fiber friction (i.e., wet and dry combing), stiffness, gloss, anti-static qualities, and strength (1). The substantivity of these cationic species to hair has been measured by various methods. These methods can be compli- cated, time-consuming, expensive, and non-quantitative. Light and electron microscopy have been used to visually evaluate the cosmetic effect of substantive proteins (2). Another non-quantitative method is the Rubine dye test in which the cationic uptake by hair is proportional to the intensity of the color developed after the reaction of an anionic dye and the adsorbed cationic compound (3). Some sophisticated means for the qualitative evaluation of the deposition of polymers and surfactants on the surface of hair include the use of the wetting force measurement 259