Eletrodos de filmes finos de mercúrio modificados com Náfion foram investigados para análise de traços de metais em amostras ambientais de águas e efluentes, pela combinação das técnicas de análise por injeção de fluxo descontínuo e de voltamentria de onda quadrada com redissolução anódica. O método, envolvendo injeção de cerca de 50 microlitros de amostras sem tratamento prévio sobre o eletrodo detector, apresenta resposta rápida. O bloqueio e o envenenamento do eletrodo são mínimos, como mostram os estudos com componentes tensoativos. Foi realizada uma comparação entre substratos de carbono vítreo e de rede de microeletrodos de fibra de carbono, com este último apresentando um pequeno aumento de sensibilidade. Como aplicação foram analisadas amostras de água de rio e de efluentes industriais, coletadas e digeridas em meio ácido para a determinação de íons zinco, cádmio, chumbo e cobre.

A perspective on the teaching of electrochemistry for science and engineering students is discussed followed by the elements and components of a wide-ranging course that can be adapted to the needs of each science and/or engineering students and, indeed, the scientific community and society at large. For all, there is a pressing need to be able to reflect critically on the knowledge gained, so that in their future careers they are able to take scientific, political and economic decisions involving different aspects of electrochemistry in the best way, particularly regarding energy, materials, health, foods and environment.

Electrochemical impedance spectroscopy is finding increasing use in electrochemical sensors and biosensors, both in their characterisation, including during successive phases of sensor construction, and in application as a quantitative determination technique. Much of the published work continues to make little use of all the information that can be furnished by full physical modelling and analysis of the impedance spectra, and thus does not throw more than a superficial light on the processes occurring. Analysis is often restricted to estimating values of charge transfer resistances without interpretation and ignoring other electrical equivalent circuit components. In this article, the important basics of electrochemical impedance for electrochemical sensors and biosensors are presented, focussing on the necessary electrical circuit elements. This is followed by examples of its use in characterisation and in electroanalytical applications, at the same time demonstrating how fuller use can be made of the information obtained from complete modelling and analysis of the data in the spectra, the values of the circuit components and their physical meaning. The future outlook for electrochemical impedance in the sensing field is discussed.

The preparation and conditioning of DNA-modified electrodes, in which glassy carbon electrodes are covered by a thick film of double-stranded DNA and subsequently conditioned in acetate buffer, has been followed with Electrochemical Impedance Spectroscopy. Spectra were recorded at different values of applied potential in order to probe the alterations occurring in the modifier layer. The alterations in the EIS response parallel the changes in voltammetric response and show that the modifier layer is a good conductor and that the behaviour as a DNA-biosensor is essentially due to surface phenomena and interaction with single-stranded DNA in solution during conditioning.

The influence of different artificial body fluids on metallic corrosion, all containing chloride ion, was investigated by measurements of open circuit potential, polarisation curves and electrochemical impedance on high speed steel, chosen owing to its high rate of corrosion. Two types of electrolyte fluid were studied, the first similar to saliva and the second to plasmatic serum and experiments were carried out over a period of immersion of 4h. Electrolytes similar to saliva were artificial saliva with and without lactic acid, and Glandosane that contains sorbitol and Na- carboxymethylcellulose organic components. Similar to plasmatic serum were phosphate buffer saline (PBS) and Krebs-Ringer solution. It was found that the organic components in the fluids partially block the metal surface and reduce the corrosion rate. From the results obtained, an approximate order of corrosion rate was established as: Artificial saliva ~ Glandosane ~ Krebs- Ringer solution < Artificial saliva without lactic acid ~ PBS. It is demonstrated that the equivalence of these different body fluids as bathing solutions should not be assumed.

Batch injection analysis (BIA) enables the investigation of electrode reactions using extremely small volumes of analyte solution of 100 pL. The potentialities of amperometric and voltammetric detection have been examined by studying the oxidation of ferrocyanide and ascorbic acid at platinum electrodes and using sample volumes between 10 and 100 pL. The electrolysis efficiency as a function of injected volume has been addressed. Consecutive injections during a slow linear potential sweep permit the registering of a point-by-point pseudo-steady-state voltammetric curve and allow the measurement of thermodynamic and kinetic parameters as well as the determination of concentration. Cyclic voltammetry during or after injection can aid in mechanistic studies. The combination of BIA and square-wave voltammetry leads to a continuous voltammetric profile from a single injection using 100 p L calibration plots show a factor of 4 sensitivity increase relative to fixed-potential amperometric detection.

Electrochemical impedance spectroscopy has been used to study the electrochemical behaviour of ternary Mg60Ti10Si30 and Mg88Ti5Si7 alloy samples fabricated by mechanical alloying of the elemental powders in an argon atmosphere. The influence of different milling times up to 25 h and heat treatment on the electrochemical behaviour of the samples, after compacting under pressure into disks, has been investigated in 0.1 M Na2SO4 and 0.01 M NaCl electrolyte solutions. Complementary measurements of open circuit potential, polarisation curves, and surface and microstructural analysis have been carried out. The experimental results revealed that corrosion is greater for Mg88Ti5Si7 which contains free magnesium; however, in sulphate solution a protective oxide layer formed can reduce the corrosion rate. In Mg60Ti10Si30, heat treatment increases corrosion, which is explained through a greater tendency for pitting corrosion. Comparison is made between the electrochemical impedance data and the nanophase structure as well as with the electrochemical behaviour of other magnesium alloys.

An electrochemical study of corrosion of Tytin® dental amalgam was carried out in electrolytes similar to body fluids: artificial saliva with or without lactic acid, a polymer-containing product of the same composition as Glandosane® and in Krebs-Ringer solution. The electrochemical techniques of open circuit potential, polarisation curves, cyclic voltammetry and electrochemical impedance were employed as a function of immersion time to characterise the surface processes occurring and bring out the differences between the different solutions. The influence of pH was tested in solutions of artificial saliva with or without lactic acid. The results demonstrated the importance of the organic component on the rate of corrosion and of adsorption phenomena on the amalgam surface.

An electrochemical impedance study of the corrosion of Tytin dental amalgam was carried out in electrolytes similar to artificial saliva with or without lactic acid, and in standard inorganic artificial saliva with higher ionic concentration. Spectra were recorded in the presence and absence of dissolved oxygen to show the importance of the formation of oxide film and the adsorption of the organic component, as well as the exposed surface microstructure. The data, supported by open circuit potential and polarisation curve experiments, obtained in the presence and absence of dissolved oxygen are interpreted in the light of possible corrosion mechanisms.