Voltammetric Soft Modelling Approach for Systems with Both Electrochemically Labile and Inert Complexes: the Zn-Glycine Case

Abstract

A multivariate curve resolution method using alternating least squares (MCR-ALS) has been applied to the study of the Zn-glycine system by polarographic techniques. The electroanalytical behavior of this system does not allow the direct application of hard modelling methods, and makes it an ideal model system to be studied by soft modelling methods. Although the condition of linearity of the current data with respect to the concentrations is not totally fulfilled, the obtained results suggest that the system is reasonably well explained considering the formation of three successive complexes, the two first ones being electrochemically labile and the third one being inert. A satisfactory resolution was achieved if during the ALS optimization the unimodality constraint was only applied to some signals (those corresponding to the free metal ion and to the first two complexes), based on the observed morphology of the experimental voltammograms. Stability constants of these complexes have been estimated from the concentration profiles obtained in the ALS optimization. They have been satisfactorily compared with stability constants from the literature, suggesting that soft modelling provides good estimations of the complexation parameters, and that it is a very useful tool for cases where hard modelling can not be applied.