A new mathematical algorithm is proposed to correct the progressive potential shift of some voltammetric signals that decrease the linearity of the data. The corrected data matrix can be further analysed by Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) and the vector including the potential shift corrections can be fitted to specific equations such as that by DeFord-Hume. A detailed discussion is given on the different cases of potential shift correction, and, in some of them, mathematical simulation is made or experimental systems [Cd(ii)-glutathione and Zn(ii)-glycine] are analysed.
The combined use of differential pulse polarography (DPP), circular dichroism (CD) and multivariate curve resolution by alternating least squares (MCR-ALS), with potential shift correction for data analysis, provides valuable information on the complexation of Pb(ii) by the phytochelatin (gamma-Glu-Cys)(3)-Gly (PC(3)). All data confirm the formation of the predominant 1 : 1 Pb-PC(3) complex. However, in the presence of an excess of Pb(ii), the same complex seems to be present but with some modification in its structure. This is suggested by the shift towards more negative potentials of the DPP signal, and by a dramatic change in CD spectra. This evolution seems to be more related to a conformational change of the complex than with a modification of the electrochemical process kinetics.
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