Portugaliae
Electrochimica Acta

The large and systematic change in cell potential (AE ) resulting from the addition of 0-l%m/m acetic acid to a mixture of ethyl or methyl acetates -20%v/v ethanol, or methanol, containing 1x10 -13 tetraethylammonium fluoride (TEAP) as background electrolyte, using fluoride electrode and calomel reference electrode filled with lithium chloride .provides a new graphical method for the rapid determination of acetic acid in ethyl or methyl acetates. Reading obtained by direct potentiometry show good reproducibility. The method is characterized by accuracy and simplicity of operation and compares favorably with the gas chromatographic method.

The interfacial region between a glassy carbon electrode and tetrabutylammonium electrolytes (halide, perchlorate and tetrafluoro - borate) in N,N-dimethylformamide has been studied using impedance techniques at varying electrolyte concentration (0.01M -í 0.20M) in the potential range 0.0 -> -2.0V vs . SCE. The spectra ca n be divided into a concentration independent low frequency part «100Hz) which is the same f o r all these electrolytes and a high frequency part depending on electrolyte and its concentration but not dc potential. Comparison is made with spectra obtained in aqueous solution. The results are discussed in terms of the physical properties of the solvent, electrolyte, glassy carbon, and the structure of the interfacial region. The low frequency feature is ascribed to electrolyte/electrode interaction s and electrode porosit, and the high frequency feature to processes involving the electrolyte anion. Keywords: glassy carbon electrode, electrode/electrolyte interface, DMF, impedance, tetrabutylammonium salts.

A general study on current reversal chronopotentiometry at spherical electrodes (as are the hanging mercury drop electrode or the static mercury drop electrode) is carried out. The effects of amalgam formation, insolubility of reaction product a n d electrode curvature on the potential l time function s are presented. The value of the ratio o f/t 2 (where f is the transition time in the reverse step and t 2 is the previous electrolysis time) can be used as diagnostic criterion to detect amalgamation or insoluble product formation. Methods to determine kinetic parameters and the formal standard potential of the electroactive couple in all the possible behaviors of the reduced species are proposed.

A simple differential pulse polarographic (DPP) method has been developed for the determination of Pipemidic acid. The Britton Robinson (BR) buffer of DH 2.07 was used as supporting electrolyte. The peak potential occurs at -809 V (SCE). The differential pulse polarographic peak height varies linearly with the concentration of pipemidic acid over the range—8.26 x 10B- — 7.41 x 10-5 M. The precision of the proposed method is excellent with relative standard deviation around 0.83% at a concentration of 6.54 x 10-6 M. Keywords: Pipemidic acid , differential pulse polarographic analysis.

Electrochemistry is on the threshold of a new era of expansion as information from novel spectroelectrochemical techniques is brought to bear on the faradaic processes taking place at electrodes. In this paper, the bases of two important techniques, ellipsometry and in situ FTIR reflectance spectroscopy, are described, and their application to a number of problems is reviewed. The first problem investigated is the adsorption and orientation of molecules on surfaces. Applications of the two techniques to problems of electrochemical promotion and polymer precursors are described. The second problem covered is the mechanism of oxidation of methanol on dispersed platinum catalysts. The evidence will be reviewed for the importance of oxide poisoning in practical systems. Data from FTIR, X-Ray Photoelectron spectroscopy and Moessbauer spectroscopy will then be summarised and the possible mechanisms for ruthenium promotion of platinum discussed in the light of the evidence. Finally, the problem of the growth of electroactive polymers on surfaces, is addressed, taking as example the growth and potential cycling of Prussian Blue films on platinum.

Basic concepts used to express the effects of temperature on the response of ion-selective electrodes (ISEs) are reviewed. A summary of results obtained in a project In progress for studying the Influence of the temperature on the response of ISEs is presented. Data have been obtained both for crystalline membrane electrodes and PYC membrane (mobile carrier) "all-solid-state" electrodes vith supports made of conductive epoxies, as veil as for crystalline membrane commercial electrodes and for PYC membrane electrodes vith internal solution. Special attention has been given to procedures to shift the isopotential point concentration to the operational concentration range of the epoxy based electrodes. It vas found that this can be implemented even for "all-solid-state" crystalline membrane electrodes, by changing the nature of the conductive epoxy used as support for application of the membrane, vhich influences the response characteristics of the electrodes.

Recent advances in the use of solid electrodes in electroanalysis are reviewed and future directions indicated, focussing particularly on hydrodynamic and pulse techniques and new electrode materials.

Copper is an essential element to all living organisms. It takes part in a range of biological processes, from electron transport to oxidation of a range of substrates [1,2], As an essential element and because of the ability to form complexes with organic substances, copper is virtually present in all living tissues [3], Despite its essentiality copper is also toxic . In some cases, the gap between the concentration levels where copper is essential or toxic is very narrow [4], This and the low concentration of copper found in the environment make it necessary to use very sensitive analytical procedures for its determination.

Stainless steel has been commonly used as a biomaterial, particulary for orthopeadic applications. Recent developments; have introduced not only other metallic alloys but also ceramic coated stainless steel to improve wear and corrosion resistance. In this work results are presented on the study of pitting corrosion of A^O^-coated and uncoated stainless steel. A significant decrease in the passivation current, was found for the coated samples

The application of Electro-Modulated Infrared Reflectance Spectroscopy (EMIRS) to electrocatalysis is illustrated by several typical examples such as the electrooxidation of formic acid at rhodium, the self-poisoning of platinum electrode, the elucidation of the electrocatalytic behaviour of polycrystalline platinum for the oxidation of methanol, the effect of Pb and Cd adatoms on the electrocatalytic activity of Rh electrodes for formic acid oxidation, and the adsorption of ethanol and of carbon dioxide at a platinum electrode.

Oxygen electroreduction is a slow reaction and, therefore, to obtain electric currents high enough for practical applications, a catalyst is needed. For this purpose many materials have been scrutinized, and surface modification of some of them to achieve higher catalytic efficiencies have been attempted. A comprehensive reference is first made to the several classes of materials tested so far. Then the techniques that have been applied to the study of oxygen electroreduction are reviewed, with some emphasis being given to the analysis of the electrochemical data. The application of these techniques are finally illustrated with a detailed discussion of the electroreduction of oxygen on pure and modified surfaces of carbon and gold.

Compounds containing the group [Mo(NO)]3+ are redox-active. Incorporation into tris(3,5-dimethylpyrazolyl)borato L*) systems, eg. [MoL*(NO)XY] where X, Y = halide, alkoxide, aryloxide, amide anilide, thiolate, etc. affords a variety of species which undergo one-electron reduction. The factors influencing this behaviour are described. Attachment of the molybdenum redox centre to macrocyclic polyethers and the effect of added cation is discussed. The group {MoL*(NO)X} can be attached to the periphery of tetra-aryl porphyrins, and the electrochemistry and photochemistry of the extra-ring metallated species is reported. A series of ferrocenyl compounds, [(i75-C5H5Fe(i75C5H4C6H4E{ML*(NO)X}]; trans-[(T?5-C5H5Fe(Tj5C5H4C6H4Z=ZC6H4E{ML*(NO)X}], where Z = CH or H, E = O or NH, M = Mo or W; X = CI or I) have been prepared, their electrochemistry investigated and several compounds identified as having non-linear optical (Secondary Harmonic Generation) properties.

Metallothioneins (MT) are sulphydryl-rich, small molecular weight proteins which form complexes with heavy metals such as cadmium, copper, mercury and zinc. Functions attributed to MT include detoxification, storage and regulation of metals. Their induction may signify exposure to excessive concentrations of metal ions in cells. Consequently, the potential value of these relatively specific biochemical indicators of metal contamination would seem to be obvious. To date however, the full value of MT as a monitoring tool has rarely been demonstrated, partly due to difficulties in determining protein concentrations. In this study differential pulse polarography has been used, together with the Brdicka electrolyte, to measure directly the levels of MT in marine organisms. The quantitative sulphydryl-specific Polarographie procedure described, is.based on the linear relationship between the height of the second of two Polarographie waves (following cobalt reduction) and the protein concentration. At room temperature, using the operating conditions described, the linear detection range was 5 - 300 ^g MT 1 , based on rabbit liver MT standard. Levels of MT-like proteins are reported for a variety of marine molluscs, collected at sites in Portugal and the United Kingdom, and range from 1.69 - 21.3 mg/g (dry weight), depending on the species and tissue analysed. The technique is clearly sensitive enough to be of value in future environmental effects assessments.

Parmi les substances neuroleptiques possédant en commun un hétéracycle central à 7 atmos avec un groupaient amidine semi-cyclique nous avons choisi le Lo:-:apine. Loxapine a été étudié pour le tecnique de polarography impuIsionel1e, extrêmement sensible, a diferent valeurs de pH et à une concentration constant. Le potential de pic dans le marge de pH étudié oscille entre 906 mV et 1240 mV.