Portugaliae
Electrochimica Acta

Potentiometric measurements have been performed, at 25 °C, in cells of the type: Reference electrode 10mol/dm-3 KCl x g d m albumin (20

The functioning of a DNA-modified glassy carbon electrode was evaluated using the electrochemical system ferricyanide/ferricyanide, after different electrode conditioning in the absence or presence of the free bases adenine and guanine, and at different applied potentials. The results were compared with those obtained at the bare glassy carbon electrode

Square wave voltammetry at microdisk gold electrodes modified with a mercury film was used to quantify nickel levels in kidney samples of mice previously treated with a solution containing those species. Comparison of the results obtained by electrochemical techniques and atomic absorption spectrometry indicates that microelectrodes are a reliable quantitative technique and greatly enhances the working conditions.

Conventional gold electrode, gold, and mercury coated microelectrodes were used to study the electrochemical behaviour of iron species in osteoblast-like cell cultures medium. Gold microelectrodes, with or without surface modification, have shown to be useful tools for in vitro qualitative and quantitative analysis of iron ions released from stainless steel in biological systems.

The influence of the temperature and the electrolyte concentration on an alkaline Fuel Cell has been studied through the variation of the current density and the potential of the cell. As anode has been utilized a palladium membrane and as cathode, a carbon-tetrafluoroethylene-perovskit porous electrode. The electrolyte used is aqueous KOH.

In this work, an UV-vis spectrophotometer technique adapted to "in-situ" absorption-reflection experiments is presented. Visible spectra at different oxidation potentials for Polypyrrole/Polyvinylsulphonate composite controlled in 0.1 M LÍCIO4 water solution were performed. The evolution of the visible-absorption spectra in the oxidized and reduced states as a function of the number of cycles of the coloration/decoloration was followed.

A bilayer structure polypyrrole-flexible and inactive polymer has been constructed to transform molecular strain in macroscopic movement during electrochemical oxidation/reduction process of polypyrrole film. With the aim of optimizing bilayer movement, the rate (rad.s-1) of those electrochemomechanical movements for a same described angle (90°), the consumed electrical charge (mC) and electrical energy (mJ) under different electrical conditions and with different bilayer dimensions has been studied. The obtained results shown an increasing of both movement rate and consumed electrical energy per mass unit at increasing applied current per mass unit (mA.mg-1). Hower the electrical charge consumed remain constant. Also the bilayer dimensions have not influence on movement rate and on consumed electrical charge or energy per mass unit. However, for a constant consumed electrical charge per mass unit the angle traveled remains constant varying bilayer dimensions.

Square wave stripping voltammetry at wall-jet mercury thin film electrodes in continuous flow has been investigated, with particular attention to the anodic stripping voltammetry of zinc, cadmium, lead and copper, and the adsorptive stripping voltammetry of cobalt and nickel via the formation of complexes with nioxime ligand. Advantages of square wave voltammetry with respect to differential pulse voltammetry in the determination step and to batch determination without continuous flow are demonstrated. Nanomolar detection limits are found. Optimisation of experimental procedures is discussed.

The electrochemical reduction of fluoxetine was studied using a hanging mercury drop electrode in different buffer solutions up to pH 13 and with concentrations of fluoxetine varying from 1.0xl0"6M to 5.0x10"5 M_- A very strong adsorption of fluoxetine on the electrode was observed and the shape of the cyclic voltammograms suggests that in these conditions it corresponds to a quasi-reversible system for adsorbed species. The results obtained for the electrochemical quantification of fluoxetine in five pharmacological formulations existing in the Portuguese market were compared.

Thiourea is a promising non-cyanide lixiviant for gold hydrometallurgy. However, its high consumption due to degradation has hindered thiourea from commercial application. Thiourea oxidation is discussed and the role of sodium sulphite as a reductant in controlling the degradation of thiourea is investigated.

The electrochemical reactions of 0.01 M CH3CH2OH and 0.01 M HCOOH on platinum in 0.1 M HC104 were studied by means of Differential Electrochemical Mass Spectrometry (DEMS). Ethanol can be oxidized to C02 and ethanol, whereas formic acid produces only C02. Electroreduction products (ethane and methane) were observed only for ethanol. The competition reactions between ethanol and formic acid were studied when both compounds are present simultaneously in the bulk of the solution (0.01 M CH3CH2OH + 0.01 M HCOOH). Using isotope labelled H13COOH it was possible to distinguish the contribution of ethanol and formic acid: formic acid oxidizes to i3C02 (m/z = 45) whereas ethanol produces 12C02 (m/z = 44). It was observed that the reactivity of ethanol is similar to that found without formic acid in the solution, whereas the production of C02 from formic acid was diminished about 50%.

Electro-oxidation and electroreduction reactions of acetylene adsorbates on gold were studied in 0.1 M HC104. It was found that acetylene forms chemisorbates in a wide potential range. On-line electrochemical mass spectrometry (DEMS) was used for the detection of the reaction products on porous polycrystalline gold electrodes. Only C02 was detected during the oxidation of the adsorbates, whereas acetylene and ethylene were identified as products of adsorbates reduction. The oxidation and reduction of the chemisorbates on single crystal faces display distinctive differences. The oxidation charge (Qox) required to oxidize acetylene adsorbed species completely to C02 depends on the adsorption potential (Uad). The shape of the curve Qox vs Uad is also affected by the structure of the gold surface.

In this work, Ni-P and Ni-P-Teflon electroless thin films were optically characterized by ellipsometry. The measured ellipsometric angles A and ¥ are used to calculate the dielectric constant spectra of these materials. Effective medium theories (Bruggeman and Maxwell-Garnett) have been employed to determine the quantity of Teflon particles in Ni-P-Teflon systems. To complement ellipsometric data, SEM/EDS and SIMS analysis have been used as well as AFM imaging.

A study of the chemistry of chromium in the passive film on Aluminium substrates after ion implantation, electrochemically grown in aqueous solutions of carbonate/bicarbonate with added chloride ions, was done by X-Ray Photoelectron Spectroscopy (XPS). The results confirmed that Cr^+ is responsible for passivation and also that pitting of Al-Cr alloys occurs when the concentration of Cr*+ in the film is reduced due to oxidization to the a more soluble species, Cr^+. Clearly, enrichment of the passive film in the solute element of the alloy is beneficial, but the pitting potential is chromium concentration dependent, exhibiting a maximum. Results will be discussed in terms of the ability of Cr to produce a more effective hydrolysis when compared to Aluminium ions.

It is proposed that the passivation region for Aluminium could be extended, outside the 4 to 9 pH range, by surface alloying with W and Ta, using ion implantation as a non-equilibrium alloying method. Extension into the acid region was achieved by surface alloying with W. This is justified in virtue of the thermodynamic stability of the solute oxide. As Tantalum exhibits passivation all across the pH range, it is reasonable to believe that passivity of Aluminium could be induced or at least greatly improved by alloying with W and Ta [1]. A fluence of 1.3E16 (W +Ta).cm"2 at different ion beam energies, (40 KeV and 150 KeV was used for surface alloying 99.999% purity Aluminium from Good Fellows Metals. The passivation of the produced implanted alloys was studied by voltammetry and impedance spectroscopy. Pre-passivated samples, in acid sulphate solutions were used in neutral 0.1M NaCl solutions. The pitting potential values are more active when polarizing without pre-exposure to acid solutions; this seems to support the idea that some Ta is lost in acid media by dissolution through the film, which is probably a mixture of Ta205 and AI2O3 in proportions that would depend on potential amongst other factors. A comparison with the values obtained using the same experimental conditions, but without pre-passivation of the sample, is made. According to the dc and ac electrochemical data the protective character of the Al implanted alloys is presumably due to the formation of a passive film containing probably a mixed oxide of Ta205 and AI2O3. The passivation model seems to agree with the solute rich interfase model [2-3], which requires that the solute forms a more protective passivating species than the Aluminium under occluded cells conditions.

The effect of perchlorate ions on the electrochemical behaviour of copper in near neutral solutions was studied using cyclic voltammetry. Results showed that perchlorate ions do not interfere with the formation of the duplex oxide film on copper in the potential range before breakdown. In fact, results seem to be in agreement with the passivation model for Cu in mild alkaline solutions. There is a solubilization of the film that gives place to Cu (I ) soluble species, that are collected at -0.875 V (SCE). Solubilization of the film acidifies the interface and precedes breakdown with nucleation and growth of pits. Soluble species of Cu (I) and Cu (n), related to breakdown, were detected in the cathodic cycle.