General theory of cathodic and anodic stripping voltammetry at solid electrodes: mathematical modeling and numerical simulations.

Theory is presented to describe the voltammetric signals associated with the stripping phase of stripping voltammetry at solid electrodes. Three mathematical models are considered, and the importance of the hemispherical diffusion associated with electrochemical dissolution of particles in the micrometer range is investigated. Model A considers a "monolayer" system where the coverage at a specific point cannot exceed a maximum value. Model B considers a thin layer of metal or metal oxide, but in contrast to model A, the maximum surface coverage is not restricted. Model C represents the stripping of a "thick layer" where the deposition is also unrestricted.

A new method for the study of processes at the liquid-liquid interface using an array of microdroplets on a au electrode.

We report the fabrication of partially blocked gold electrodes, with regularly and hexagonally spaced inert hydrophobic blocks on their surface. The hydrophobic blocks, with diameters of 5 mum, are used to support liquid 5-nonyl-salicylaldoxime (Acorga-P50) droplets on the surface. By voltametrically monitoring the transport-controlled reduction rate of Cu(II) (in pH 5 solution) at the unblocked part of the gold surface it is possible to deduce, via simulation, the parameters controlling the rate of uptake of Cu(II) at the droplet-aqueous solution interface as the droplet "fills up" with Cu(II). Experimentally, it is recorded that the reduction current increases until the droplet is filled completely; after this, there is no further noticeable effect of the droplet coating. A rigorous theoretical analysis of the transients permits the deduction of partition coefficients between the aqueous solution and the organic-droplet phase and of diffusion coefficients within the droplet. The partition coefficient for Cu(II) between water and 5-nonyl-salicylaldoxime was found to be 200 at 25 degrees C and the diffusion coefficient of Cu(II) inside the organic phase was determined to be 5 x 10(-11) cm2 s(-1).

Voltammetric sizing of a sphere.

The size of a glass sphere positioned in the center of a microdisk electrode is determined by using a simple electrochemical procedure and is confirmed, additionally, by a microscopical measurement of the sphere at the time of the electrochemical measurement. The cyclic voltammetric response of the naked electrode and of the electrode with the sphere positioned in its center is recorded over a wide range of scan rates (0.002-1.5 V s(-1)). The size of the sphere is then determined by comparison of the experimental voltammogram with simulations for each individual scan rate.

Mathematical modelling and simulation of adsorption processes at spherical microparticles.

A model for the adsorption process at spherical microparticles under transient diffusion conditions has been developed and solved using numerical simulation. This model allowed us to demonstrate that the system is controlled by two main dimensionless parameters: the adsorption rate constant ka' and the saturation parameter beta. Analytical models for the adsorption process at spherical microparticles under steady-state mass transport conditions have been derived. These models use previously developed empirical relationships for the calculation of the mass transfer coefficient (kc). The properties of the system were studied for both the case where mass transport is described by diffusion only and the case where it is the result of a coupled diffusion/convection process. These mathematical tools were then used to analyse the results obtained for the uptake of CuII by glassy carbon powder modified with the monomer L-cysteine methyl ester and to extract a minimum value for the adsorption rate constant which was found to be of the order of 10(-4) cm s(-1).