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Calibration curves built up from normal pulse polarography limiting currents are discussed. The following basic assumption is made: labile metal macromolecule complexation, induced adsorption and reversible electrochemical reduction. Nonlinear plots are obtained, either from homogeneous complexation (if ligand is not in excess) or from non-linear adsorption regimes. In the latter case, an analytical expression for the current under strong adsorption, saturation and excess ligand conditions is reported. Moreover, differences on the time dependence of limiting currents under Langmuirian and Henry regimes are also discussed. Non-ligand excess results show that adsorption leads to erroneous equivalence points in titration plots.

A semi-empirical expression is proposed for the normal pulse polarographic wave of the reduction of a metal ion in a labile metal-polyelectrolyte system, in the presence of an excess of ligand, and includes both the polyelectrolytic ligand adsorption and the induced adsorption of the metal ion. This expression avoids the need to know the values of the adsorption isotherms of both the complex and the polyelectrolytic ligand as well as their time and potential dependences. A non-linear fitting procedure is performed in order to obtain the parameters of the semi-empirical expression, from which an approximate value of the stability constant of the complex can be estimated. The accuracy of this semi-empirical expression is tested by simulated curves, and it is applied to experimental results for the Cd(II)-polymethacrylate complex, in order to obtain the stability constant of the complex from experimental data in the presence of adsorption phenomena.

A theoretical model is developed for describing the reduction, by normal-pulse polarography, of a metal ion in the presence of a macromolecular ligand, including both the ligand adsorption and the induced adsorption of the metal ion. The following basic assumptions are made: reversible charge transfer at a stationary planar electrode (static mecury drop electrode); labile complex; large excess of ligand compared with the total metal concentration; Langmuirian adsorption for both the ligand and complex species; and diffusion coefficients for ligand and complex species very different from that of the free metal. The mathematical approach is based on transforming the system of differential equations with their boundary conditions into an integral equation which has been solved numerically. A simple procedure to obtain stability constants and adsorption parameters simultaneously from the experimental data is described. This model has been used to reproduce some experimental data from the Cd(II)—polymethacrylate system.