Phosphonate complexes. Part 5. An improved multiparametric refinement program, MUCOMP, for complex formation studies from potentiometric data

Abstract

A new version of the refinement program MUCOMP is described. The stability constants of the complex species as well as the parameters liable to comport systematic errors (total concentration of main components and of impurities, and electrodes characteristics) are adjusted so as to minimize the weighted error-square sum of the added volume, the partial derivatives with respect to the unknown parameters being evaluated analytically. A generalized Newton–Raphson method is employed for the simultaneous calculation of the free concentrations and of the added volume. To deal with carbonate-contaminated reagents and the subsequent carbon dioxide evolution which occurs during titrations under nitrogen flow, an appropriate function for carbon dioxide departure is introduced in the proton balance and the corresponding equilibrium defect is taken into account in the weighting procedure.