Voltammetric currents for any ligand-to-metal concentration ratio in fully labile metal-macromolecular complexation. Easy computations, analytical properties of the currents and graphical method to estimate the stability constant
Monné Esquerda, Josep
Mas i Pujadas, Francesc
MetadataShow full item record
In order to enable a wider use of voltammetric methods in speciation analysis, it is convenient not to be restricted by ligand excess conditions. This work assumes labile ideal complexation of a metal ion by a ligand, planar electrode, no electrodic adsorption and equal diffusion coefficients for the complex and the ligand, but very different from the metal ion. It is shown that the system of non-linear equations describing the diffusion of the species in a potentiostatic experiment for any ligand to metal ratio can be reduced to only one ordinary differential equation by means of a change of variable. Standard numerical methods can then be used in the computation of the solution with a great saving of computational time and resources in comparison with other existing methods. Some properties of the currents are also proved: (i) Cottrellian behaviour for any current in normal pulse polarography (NPP) and for limiting currents in reverse pulse polarography (RPP), (ii) the dependence of the normalised limiting current (φ) on just three parameters, and (iii) the equality of limiting NPP and RPP currents. The normalised current for high stability constant values depends on just two parameters, one of which is the ratio of total metal/total ligand concentrations, and can be found from an implicit algebraic equation. A new representation for the normalised limiting currents is suggested: the iso-φ diagram, which for each ratio of diffusion coefficients, ε, describes the currents for any stability constant in a unique drawing. A new graphical procedure arising from this diagram is suggested and then applied to data corresponding to Zn/poly(methacrylic) acid at pH 6 and fixed ionic strength.
Is part ofJournal of Electroanalytical Chemistry, 1999, vol. 472, num. 1, p. 42-52
European research projects
Showing items related by title, author, creator and subject.
Complexation isotherms in metal speciation studies at trace concentration levels. Voltammetric techniques in environmental samples Garcés, Josep Lluís; Mas i Pujadas, Francesc; Cecília Averós, Joan; Companys Ferran, Encarnació; Galceran Nogués, Josep; Salvador Turégano, José; Puy Llorens, Jaume (Royal Society of Chemistry (Gran Bretanya), 2002)Is any complexation isotherm valid to analyse macromolecular binding of trace metal ions in environmental samples? To answer this question, a detailed study of the behaviour of some usual complexation isotherms with different ...
Evaluation of the Koutecký-Koryta approximation for voltammetric currents generated by metal complex systems with various labilities Leeuwen, Herman P. van; Puy Llorens, Jaume; Galceran i Nogués, Josep; Cecilia Averós, Joan (Elsevier, 2002)The voltammetric response of metal complex systems with various labilities is analyzed by rigorous numerical simulation with the Finite Element Method of the time-dependent concentration profiles of the different species. ...
Electrostatic and specific binding to macromolecular ligands: a general analytical expression for the Donnan volume Companys Ferran, Encarnació; Garcés, Josep Lluís; Salvador, José; Galceran i Nogués, Josep; Puy Llorens, Jaume; Mas i Pujadas, Francesc (Elsevier, 2007)The dependence of the apparent acid dissociation constant of charged polyacids on the ionic strength and on the degree of dissociation is analysed in terms of the Donnan model. We introduce a new approximate analytical ...