Multivariate curve resolution analysis of voltammetric data obtained at different time windows:: study of the system Cd2+-nitrilotriacetic acid

The system Cd2+-nitrilotriacetic acid (NTA) has been studied by voltammetric techniques with different time windows (long drop time direct current polarography, differential pulse polarography and differential pulse anodic stripping voltammetry), in a way that, depending on the technique, the 1:1 complex behaves mainly labile or mainly inert. The corresponding signals have been treated by using two different approaches: hard modelling (i.e., the usual strategy in electrochemistry which requires a priori postulated models) and soft modelling (i.e., by means of purely mathematical data analysis using a family of factor analysis techniques). The results have been compared with each other and also with the values in the literature. It was found that soft modelling is especially accurate in the case of inert complexes, even when a small fraction of the complex dissociates during the voltammetric measurement. However, for systems that are closer to lability (i.e., with an important fraction of complex dissociation) soft modelling just provides rough estimations of the complexation parameters that, anyway, can be useful when a basis for the hard model approach is not available. (C) 1998 Elsevier Science B.V. All rights reserved.