Portugaliae
Electrochimica Acta

The potentialities and limitations of electrochemical methods in the study of trace metal speciation in natural waters will be focused, as well as the factors influencing the voltammetric signal, with a special emphasis on the diffusion coefficient of labile macromolecular systems. Some applications of voltammetric techniques to the speciation of trace metals in natural samples are presented, namely with humic matter, estuary and seawaters.

A procedure for the quantitative analysis of mixtures of acids, based in the treatment of data of potentiometric pH titrations by multivariate chemometric calibration methods, is presented. Experimentally, the procedure consists in the titration of a set of mixtures of acids similar to the sample, but with known concentration of the components, which constitute the calibration set. A two step data analysis procedure is used for the development of calibration models: (i) the raw titration curves are adjusted to a polynomial equation of the fifth degree and the inverted titration curves are obtained (volume as function of the pH); (ii) the inverted titration curves are used to develop calibration models, using multivariate chemometric methods like partial least squares and artificial neural networks which can deal with some non-linearity in the basic inverted model. The results showed that adequate predictions of the concentration of the acids of the mixture are obtained.

The incorporation of metals in organic conducting polymers by electroless deposition is demonstrated for Ni-P on electropolymerized polyaniline films. The creation of starting catalytic conditions for effective nickel electroless deposition is discussed and the influence of the electropolymerization conditions on the metal particles dispersion is analysed. Nickel electroless deposition has been carried out on polymer films built up to various thicknesses in order to produce several metallic contents and / or different sized Ni-P particles. The so-obtained modified electrodes have been characterised including its redox behaviour.

The electrochemical behaviour of Vitamin BI2 derivatives with cobalt (III) complex and containing an alkyl chain with a peripherical pyrrole group is analysed by cyclic voltammetry. Adsorption of the derivatives under oxidised and reduced forms appears to allow the oxidation of the pyrrole group with concomitant polymer film formation. The length of the alkyl chain has been seen to play an important role on the polymer properties namely on its conductivity and thus on the possibility of thickening the film. Although a relatively high potential is required for the adequate monomer oxidation the electropolymerization of these new monomers can be envisaged for modified electrodes preparation.

Estudou-se a influência do ião Fe2' na biocorrosão de um aço macio, na presença e na ausência de bactérias redutoras de sulfato (SRB). Os estudos foram realizados por voltametria cíclica, curvas de polarização de estado quasi-estacionário e perda de massa. Os resultados indicaram que o aço é mais susceptível à corrosão quando o ião Fe2+ está presente no meio.

The performance of an ion selective electrode array (ISEAR), designed for the determination of benzoate in the presence of iodide, constituted by all-solid-state electrodes with Aliquat 336 S or tetraocrylammonium salts immobilised in PVC membranes, is described. The response of the ISEAR to both ions was obtained by two treatments: (i) calculation by non-linear least squares (NLS) of the parameters of a model based on the Nikolskii-Eisenmann equation; and (ii) principal components regression (PCR). The results are compared and discussed. Results obtained in the determination of benzoate in pharmaceutical formulations containing iodide are included.

This session intends to celebrate the 5t n anniversary of the Portuguese Electrochemical Society by presenting an account on the establishment of the electrochemistry as a science and on its development at the Portuguese Universities, as well as a reference on the role of that society on the evolution of this science within the Portuguese scientific community. The former aspects will be presented by the invited speakers, whereas the latter are considered now, in the opening of the session.