Soft modelling approach applied to voltammetric data: study of electrochemically labile metal-glycine complexes

The systems Cd2+-glycine and Pb2+-glycine, which form successive electroche mically labile complexes, were studied by several polarographic techniques: differential pulse, normal pulse and reverse pulse polarography. The volta mmetric data were analysed by both the classical DeFord-Hume method (a hard modelling approach) and by a multivariate curve resolution method based on different factor analysis techniques (a soft modelling approach). The resu lts have been compared with each other and also with those from the literat ure. It was found that while for labile complexes the necessary (for factor analysis techniques) condition of linearity of the current with respect to the concentrations is not always completely fulfilled, the results obtaine d by the two approaches are very similar. This suggests that for these syst ems the fraction of non-linearity of the signals is small and can be neglec ted. Thus, the proposed soft modelling approach also provided good estimati ons of the complexation parameters, and is suitable for use as a complement ary tool on the study of systems with successive labile complexes. (C) 2001 Elsevier Science B.V. All rights reserved.