title: Study of monoprotic acid-base equilibria in aqueous micellar solutions of nonionic surfactants using spectrophotometry and chemometrics.
abstract: Many studies have shown the distribution of solutes between aqueous phase and micellar pseudo-phase in aqueous micellar solutions. However, spectrophotometric studies of acid-base equilibria in these media do not confirm such distribution because of the collinearity between concentrations of chemical species in the two phases. The collinearity causes the number of detected species to be equal to the number of species in a homogenous solution that automatically misinterpreted as homogeneity of micellar solutions, therefore the collinearity is often neglected. This interpretation is in contradiction to the distribution theory in micellar media that must be avoided. Acid-base equilibrium of an indicator was studied in aqueous micellar solutions of a nonionic surfactant to address the collinearity using UV/Visible spectrophotometry. Simultaneous analysis (matrix augmentation) of the equilibrium and solvation data was applied to eliminate the collinearity from the equilibrium data. A model was then suggested for the equilibrium that was fitted to the augmented data to estimate distribution coefficients of the species between the two phases. Moreover, complete resolution of concentration and spectral profiles of species in each phase was achieved.
authors.affiliation: University of Copenhagen, Faculty of Science, Department of Food Science, Spectroscopy & Chemometrics Section, Rolighedsvej 30, DK-1958 Frederiksberg, Denmark. Electronic address: hamba@food.ku.dk.
authors.forename: Hamid
authors.initials: H
authors.lastname: Babamoradi
authors.affiliation: Institute for Advanced Studies in Basic Sciences (IASBS), Department of Chemistry, 45137-66731 Zanjan, Iran.
authors.forename: Hamid
authors.initials: H
authors.lastname: Abdollahi
keywords: Acid–base equilibria; Distribution coefficient; Matrix augmentation; Micelle; Rank deficiency; Spectrophotometry