Portugaliae
Electrochimica Acta

Insulin-zinc suspensions are more electroactive on the hanging mercury drop electrode (hmde) when the protein is in amorphous state. Reduction and reoxidation of disulphide bridges depend on the Zn(II) present in buffer solutions. The influence of the insulin adsorption on the reduction process of zinc at the hmde, can be explained by variation oi the exchange- current, density with a change in the surface fraction covered by the protein on the electrode.

Prussian blue (PB) has been electrodeposited on ITO-glass coated electrode. Electrochromism effect, stability of the film against continued ciclation of potential and influence of nitrate and chloride ions has been studied.

A critical review of the ca.. 100 papers in which ion-selective electrodes (ISEs) are used as detectors in flow-injection analysis (FIA) systems is presented, with the purpose of identifying systematic patterns of utilization. Three points, the insertion of the ISEs in F IA systems, the characteristics of F IA systems in which ISEs are used, and their analytical applications, are considered in turn.

Modern theory of ionic solutions depends upon information on a variety of experimental methods for a realistic adjustment of parameters. Hamiltonian models yield reliable equations for various solution properties with a unique set of basic parameters resulting from fits of different appropriate experiments, thus permitting the simulation of the properties of other electrolyte solutions for which data are not available. In this way knowledge-based data bases provide the property profiles of electrolyte solutions for applied research and technology. A survey is given of the information on structure and dynamics of electrolyte solutions obtained from high frequency permittivity measurements and of chemical models at McMillan-Mayer level permitting the calculation of electrolyte solution properties. The interplay of thermodynamic, transport, spectroscopic, kinetic and computer simulation methods is stressed. Illustrative examples are quoted.

The principle of fast techniques in direct electrochemistry is presented, and the domain of their applicability is examined on the basis of classical theories. In this process two series of factors are identified which limit the method. In the one hand, ohmic drop, capacitive phenomena and coupling of diffuse and diffusion layers are intrinsic factors. They lead to built-in limitations of the time scale range of the method. These limits cannot be trespassed without the necessity of introducing severe modifications of the available theories of molecular electrochemistry. On the other hand, other limitations exist which are only due to the present technology, and are therefore expected to be broken in the future.

An electroanalytical study of the cytarabine reduction process at a dropping mercury electrode in aqueous supporting electrolyte solution using direct current polarographic technique has been carried out. The optimum parameters were found as 1000 dyne.cnr2 pressure on the mercury reservoir, Is drop time, 4 mV.s"1 scan rate and 5.50-6.60 pH range. The reversibility of the reduction on the mercury electrode was ascertained as quasi-reversible and the polarographic current was mainly diffusion controlled. The results obtained by DC, SIAP and DP polarography allowed a method developed for the determination of cytarabine in the lxlO-4 - 5xl04 mol.L"1 concentration range. Good results were obtained by applying the DC polarographic technique to the determination of cytarabine in a pharmaceutical preparation.

The experimental conclusions on the chemical-kinetic process of the chemical plating on ABS surface, one of the plastics materials more widely used, are presented, describing each step of the process

In the anodic methanol oxidation in aqueous sulphuric acid on smooth R-electrodes using the chronopotentyometric method, oscillations of potential in the V=V(t)-curves have been observed. The evolution of such potential oscillations with the value of the current impulse imposed on the electrodes has been discussed and a reaction mechanism of the methanol oxidation has been proposed in accordance with the experimental results

The corrosion products formed on weathering steel and pure iron exposed to a wet-dry cycled SO2~atmosphere have been studied by means of reflection (CEMS) and transmission Mossbauer spectroscopy and X-ray diffraction. After 48 days of exposure, rusts of both materials exhibit different morphologies. FeS03.3H20, FeS04.nH20 and amorphous ferric oxyhydroxides (probably ferrihydrite and/or a-FeOOH of small particle size) are the constituents of both rusts. The main differences between the corrosion products of both materials are related with the concentration of Fe2* species and the crystallinity and/or particle size of ferric oxyhydroxides. The presence of Fe?+ species in 48 day-old rusts is attributed to the effect of the wet-dry cycling conditions.

The effect o-f the imidazoles I-III (1) on the deposition velocity o-f cooper on phenolic and epoxy resins has been studied. It is shown that these substances affect the stability of the cooper electroless baths in the temperature interval 25-52 ºC.

In solution containing chloride anions, the pitting corrosion can be obtained when the electrode potential exceeds a certain critical value (Ep). The initiation of pitting corrosion has been considered as a rare even both in space and time and consequently, it can be treated as a statistical phenomenon (1-4). The pitting corrosion of. 304 stainless steel (304 SS) in a strong buffered chloride ions containing medium has been studied by using the potentiodynamic and potentiostatic techniques complemented with scanning electron microscopy observations.