On the determination of the critical micelle concentration by the pyrene 1:3 ratio method

The aim of this paper is to establish a simple and accurate approach to the treatment of pyrene 1:3 ratio data in the context of critical micelle concentration determination in surfactant solutions. The procedure we propose is based on the assumption that pyrene 1:3 ratio data are properly fitted by a Boltzmann-type sigmoid. From the fitting parameters we consider two singular points as possible candidates to determine the critical micelle concentration of the surfactant, adopting objective criteria for the election of one or the other point. With the purpose of supporting our contention, numerous specific examples are presented and discussed, including single ionic and nonionic surfactants, micellization of surfactants in the presence of additives, and several mixed-surfactant systems. In all the cases examined the experimental data were well fitted by a decreasing sigmoid of the Boltzmann type, and the proposed approach worked in an appropriate way, providing critical micelle concentration values in good agreement with those in the literature obtained using different methods. (C) 2003 Elsevier Science (USA). All rights reserved.