Browsing by Subject "Analytical theory"

Now showing 1 - 3 of 3
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    Analytical theory for ion transfer-electron transfer coupled reactions at redox layer/thick film-modified electrodes
    (Elsevier, 2020-02) Laborda, Eduardo; González Sánchez, Joaquín; Molina, Angela; Química Física
    Electrodes modified by liquid films or plasticized polymeric membranes containing a redox species offer valuable alternatives for the study of ion transfers and bimolecular electron transfers at liquid|liquid interfaces with conventional electrode arrangements and stable interfaces. The ion-to-electron (or electron-to-electron) transducer affects the electrochemical signal, complicating the accurate analysis of experimental data. This can be reduced through the use of an electrode surface-attached redox species of well-defined electrochemical behaviour. As will be demonstrated, the voltammetry of these systems show significant deviations with respect to individual charge transfers, which must be considered for appropriate diagnosis and quantitative analysis. For this, a simple analytical theory is presented here, deducing mathematical expressions for the current-potential response, as well as for the potential difference at the two polarized interfaces, the surface excess of the redox species and the ion interfacial concentrations.
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    Guidelines for the voltammetric study of electrode reactions with coupled chemical kinetics at an arbitrary electrode geometry
    (ACS Publications, 2019-04-02) López Tenés, Manuela; Laborda Ochando, Eduardo; Molina Gómez, Ángela; Compton, Richard G.; Química Física
    A powerful, unified, and simplifying mathematical approach for the theoretical treatment of first-order chemical kinetics coupled to interfacial charge transfers at electrodes of arbitrary geometry and size, both uniformly accessible and nonuniformly accessible to the electroactive species, is presented. The general CEC mechanism at spherical and disc electrodes is considered to test the validity and benefits of such an approach, based on the application of the so-called kinetic steady state, that enables the reduction of the multivariable problem of kinetic-diffusive differential equations to a single variable problem of a diffusion-only differential equation. This is solved both analytically and numerically, showing how this approach leads to general, simple, and efficient solutions for the study of the influence of coupled chemical kinetics on the voltammetric response. The voltammetry of the CEC mechanism is analyzed as a function of the kinetics and thermodynamics of the preceding and subsequent chemical reactions and of the electrode size (from macroelectrodes to ultramicroelectrodes) and shape (spherical and disc). Comparison with the responses of the CE, EC, and E mechanisms is included, proposing diagnosis criteria and procedures for quantitative analysis of experimental data.
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    Theoretical treatment of ion transfers in two polarisable interface systems when the analyte has access to both interfaces.
    (American Chemical Society (ACS), 2018) Olmos Martínez, José Manuel; Molina Gómez, María de los Ángeles; Laborda Ochando, Eduardo; Millán-Barrios, Enrique; Ortuño Sánchez-Pedreño, Joaquín Ángel; Química Analítica
    A new theory is presented to tackle the study of transfer processes of hydrophilic ions in two polarisable interface systems when the analyte is initially present in both aqueous phases. The treatment is applied to macrointerfaces (linear diffusion) and microholes (highly convergent diffusion), obtaining analytical equations for the current response in any voltammetric technique. The novel equations predict two signals in the current-potential curves that are symmetric when the compositions of the aqueous phases are identical while asymmetries appear otherwise. The theoretical results show good agreement with the experimental behaviour of the “double transfer voltammograms” reported by Dryfe et al. in cyclic voltammetry (CV) (Anal. Chem. 2013, 86, 435-442) as well as with cyclic square wave voltammetry (cSWV) experiments here performed. The theoretical treatment is also extended to the situation where the target ion is lipophylic and it is initially present in the organic phase. The theory predicts an opposite effect of the lipophilicity of the ion on the shape of the voltammograms, which is validated experimentally via both CV and cSWV. For the above two cases, simple and manageable expressions and diagnosis criteria are derived for the qualitative and quantitative study of ions lipophilicity. The formal ion-transfer potentials can be easily quantified from the separation between the two signals making use of explicit analytical equations.