Implementation of a chemical equilibrium constraint in the multivariate curve resolution of voltammograms from systems with successive metal complexes

Abstract

A multivariate curve resolution (MCR) method, using a constrained alternating least squares (ALS) procedure with a new chemical equilibrium constraint, was applied to differential-pulse polarograms of successive metal complexes. This new restriction imposes the fulfillment of a chemical model defined by a set of stability constants that are optimised along the iterative ALS procedure. The reliability of the method was tested with simulated data and with polarograms measured for the systems Zn(II) + glutathione and Cd(II) + 1,10-phenanthroline. These systems respectively yield two and three successive and electroactive complexes, which are inert from the electrochemical point of view, that is, the complexes virtually do not dissociate during the measurement. Although the presence of electrode adsorption could induce overestimation of some concentrations and losses of linearity between concentrations and signals, the results showed that the proposed method can yield satisfactory estimations of the stability constants in this kind of system. The performance of the new method is compared with the performances obtained using MCR-ALS without the equilibrium constraint and using traditional curve fitting least-squares approaches.

Rank annihilation factor analysis for spectrophotometric study of complex formation equilibria

“…Hard-soft-modeling equals or overcomes the performance of hard-and soft-modeling in any case. The potential usefulness of the novel methodology in kinetics and equilibrium studies is reported by some researchers [19,32,34].…”

“…Several softand hard-modeling algorithms have been developed that analyze bilinear data obtained from chemical systems. Examples include kinetics, equilibrium studies and chromatography [19][20][21][22]. Soft-modeling methods range from very general approaches with minimal demands on the structure of data, such as EFA [23], HELP [24], SIMPLISMA [25] and ALS [26], to methods which rely on trilinearity, such as PARAFAC [27], GRAM [28] or TLD [29].…”

Target transform fitting in a voltammetric study of metal complexation

“…In spite of the fact that in most cases electroanalytical data are not totally linear with respect to the bulk concentration of species; studies have shown that under certain conditions, i.e. inert complexation systems in electrochemical point of view (those which association-dissociation rates of the complexes is slower compared with the time scale of the measurement), analyzing such data matrices by ordinary linear chemometric techniques can produce acceptable results close to those obtained by means of the rigorous electrochemical model [5].…”

“…1). It is reported that the currents produced by many of ligands are not linear with respect to the free ligand concentration [5]. The non-linear contribution of L in data was taken into account by changing the original simulated concentration pro- ).…”

“…They developed multivariate curve resolution with alternating least squares (MCR-ALS) as a soft-model data analysis method to resolve successive complexation systems and reported overall formation constants for species which were formed [2,[5][6][7].…”