Portugaliae
Electrochimica Acta

The Polarographie characteristics of the NKI I) ion in presence of the four aminoalcohols monoethanolamine, N-methylethanolamine, N-ethylethanolamine and N,N-dimethylethanolamine are reported. In general, half-wave potentials for the complexes are more positive than for the aquo-ion, and shift towards more negative values as the concentration of ligand increases. Transfer coefficients, <*c, electrode reactions rates and activation energies were determined for the reduction of the complexes. Differences between the reduction mechanism of the various NKI I)- aminoalcohol complexes are pointed out.

The voltammetric behaviour (d.c. and d.p.v.) of the pesticides Fenthion and Fenitrothion on a glassy carbon electrode is described. Fenthion is oxidized at + i.20 V (vs Ag/AgCl) but Fenitrothion is reduced at - 0.60 V. Both electroanalytical responses can be used for the determination of the two pesticides with detection limits of 1.36 and 0.46 uM, respectively.

The polarographic behaviour of Co(II) in Britton-Robinson media is studied by Kalousek's polarographic methods. The experimental contribution at the study of the reduction of Co(II) and re-oxidation of Co(0), mechanism which takes place on the d.m.e.is discussed. The na^ and na^ values correspond to processes where monoelectronic transfer steps are coupled with chemical-physical steps.

Differential pulse polarography and anodic stripping voltammetry can be used directly in suspensions without pre-filtration; heavy metals like copper(II) and lead(II) adsorbed on hydrous oxides such as silica and ct-goethite are not being released during the time scale of the techniques and are thus not sensed by these techniques. In samples with colloids and organics such as EDTA and NTA in the presence of heavy metals, when the complexes are non-labile but electro-chemically reducible at a more negative potential, one can determine the ligand concentration and the binding capacity of the colloid from the voltammetric measurements of individual batches with different amounts of cations like copper(II) and lead(II). From the differential pulse measurements of solutions with heavy metals and the organic ligands EDTA and NTA, it is possible to know directly the amount of metal bound to each one of the ligands and the free cation. This can also be determined by anodic stripping voltammetry at different deposition potentials.

The synthesis and the differential pulse polarographic analysis of ten 6-acyl-2(3)-benzoxazolone derivatives are presented. pH 3.00 Britton-Robinson buffer was found to be.the best supporting electrolyte. The electrochemical determination is based on the reduction of carbonyl group present in all molecules. Linear response was observed from 0.2-2 to 25-65 mg.L depending on the molecules.

The Electrochemical behaviour of mild steel in equimolar carbonate/bicarbonate solutions was investigated by means of cyclic voltammetry. In the pre-passive region the presence of three anodic peaks (peak I, II and III) indicated the participation of Fe(0), Fe(II) and Fe(III) in the electrochemical processes. The participation of carbonate/bicarbonate species in this region was detected by X-Rays diffraction. At potentials > + 0.800 V (SCE) the transpassive region begins with a sharp increase in current giving place to a novel peak preceding oxygen evolution. This peak is associated to Fe(VI) species, also being observed by the authors in the absence of carbonate/bicarbonate for solutions of NaOH with pH > 11.06. The reduction peaks detected in the reverse scan (peaks VI, VIII and IX) correspond to the anodic peaks V, III and II respectively. This characterization was made by sweep reversal studies. A subsequent chemical reaction is thought to be coupled to the electrochemical processes taking place in the transpassive region. The present research work aims to contribute determination of the mechanism in the transpassive Further work related to the characterization transpassive peak is in progress.

Studies of passive film on AISI 304 stainless steel in alkaline medium (pH = 9.2) with and without Cl~ addition were carried out by using photoelectrochemical and impedance techniques. For the band gap energy of the oxide film values of 2.65 - 2.75 eV were estimated and for the flat potentials values between -430 and -530mV (SCE) were calculated. The variation of the capacitance of the film with the potential of its formation was also studied.

The ability of certain polymers to complex with a variety of salts and form electrolytes has been known for more than a decade. These polymer electrolytes can be manufactured in thin films with moderate conductivity, have a broad voltage stability window and form a deformable, stable interface with many electrode materials. As a result of these properties polymer electrolytes offer unique advantages in solid state batteries. Several aspects of the preparation and performance of these electrolytes are discussed in this article.

A brief critical review is given on the methods usually adopted in processing atmospheric corrosion data. Kinetics of atmospheric corrosion of iron in a marine environment (Sines) are found to follow a linear bilogarithmic relationship, reliable enough to provide good estimates of total losses – as well as corrosion rates - up to 10 years. Keywords: atmospheric corrosion kinetics; iron; marine environment; outliers; linear bilogarithmic law.

"Major" and "minor" experimental parameters that can influence the catalytic activity of a polycrystalline Pt electrode, in an acid aqueous medium, are emphasized. Typical results, demonstrating such effects are presented. It is also shown that cyclic voltammetry is a powerful technique, for activation and control of the state of the working Pt surface and also for control of impurities in the base electrolyte solution. However, the aim of this paper is to give some advices to all those that have to work with Pt. for the purpose of comparing catalytic activity, induced by different means.

Measurements of the differential capacity of a Hg electrode in contact with six aqueous solutions of urea were made using a computer controlled system which sampled 75 times during the drop life. The parameters of the adsorption isotherm are determined under appropriate thermodynamic conditions. The results indicate that urea adsorbs much less strongly than thiourea.

Ideally a lithium ion-selective electrode should detect 0.1mM lithium in the presence of about 150mH sodium as well as the usual blood components. About 40 cyclic and acyclic ionophores have been examined potentiometrically. PVC electrodes with three such ionophores have been evaluated for the analysis of real sera using a micro conduit flow injection technique. Each of the sensors suffered serious interferences from unidentified serum components.

A bromide selective electrode based on mercury salts applied to a support of electrically conductive epoxy has been prepared and tested. A 2:1 (by weight) mixture of mercurous bromide and mercuric sulphide was used as sensor. Response characteristics to bromide and mercurous ion were determined by standard procedures, showing that the electrode responds to bromide as a second kind electrode. The electrode shows a better performance than the PHI 91300 Graphic Controls commercial electrode, which uses the same type of sensor.

Mean ionic activity coefficients of tetraethyl-ammonium(TEA) Perchlorate in aqueous solutions have been calculated from the effect of the TEA salt on the perchloric acid activity coefficients. Acid activity coefficients have been determined by measuring the emf of a concentration cell. Parameters º, ^ and Cø in Pitzer's equations have also been calculated for a series of substituted ammonium salts using both previously reported data and our TEA Perchlorate values. . Keywords: activity coefficients, tetraethylammonium perchlorate, electrochemical cell measurements.

The polarographic behaviour of clobazam was investigated over a wide pH range. Different types of peaks were obtained depending on the pH. Characterization of the electroactive process included an examination of the degree of reversibility, electrocapillary curves, influence of surfactant agents and the effect on the peak current of pulse amplitude, ionic strength, drop time, temperature and clobazam concentration. A method for the determination of clobazam, with a detection limit of 46x10"7 M and a relative standard deviation of 0.97% is proposed.

The transfer of electrons across the electrode-solution interface has long been the subject of much research, not only from a fundamental point of view, but also because of its importance in electrocatalysis and other reactions of industrial interest. Electron transfer is very often coupled with preceding or following chemical reactions, so that elucidation of the full reaction mechanism and kinetics is more complex. With the advent of hydrodynamic electrodes and, more recently, greatly improved ways of analysing electrical transients, significant developments in the study of electrode kinetics have occurred. These advances will be surveyed and future prospects indicated.

The surface concentration effect of the metal ion during the stripping step of ASV, in a complexing medium, is discussed in terms of determination of stability constants, from the results for Pb(II) + TETA system. Subsequently, stability constants of Cd(II) + carboxy-phenyliminodiacetic acid, phenylmethyliminodiacetic acid, pyridine-2,6-dicarboxylic acid and pyridine-2-carboxylic acid have been determined and the values compared with those obtained by other techniques.

Potassium Ion Selective Electrode with a PVC Membrane Applied to a Conductive Epoxy Support. A new technique for the construction of "all solid state" PVC membrane electrodes which consists of direct formation of the membrane on a support of silver loaded conductive epoxy is described. The response characteristics of a potassium electrode with the Corning 47731 7 sensor prepared by this technique are presented. The electrode shows performance similar to the conventional (with internal solution) electrode with the same sensor, but longer durability. The advantages and shortcomings of the present construction technique over the procedures previously described for the assembly of PVC membrane electrodes (of conventional or "coated-wire" types) are discussed.

ABSTRACT Green solutions of [CuL(H20)] [ClO4]2.H20 (L=C30H24N6; structure below) in acetonitrile slowly become red. The process can be followed by cyclic voltammetry and differential pulse polarography. An initial reversible one-electron redox process vanishes with time; concurrently another appears, at more negative potentials. This behaviour will be described and discussed. KEYWORDS: colour change in solution; cyclic voltammetry; differential pulse polarography