KINETIC CLASSIFICATION OF METAL-COMPLEXES IN ELECTROANALYTICAL SPECIATION

The application of electroanalytical methods to metal speciation studies requires the distinction between labile, quasi-labile and non-labile metal complexes. Quasi-labile behaviour is quantitatively defined in terms of the kinetic parameters of association/dissociation of the complex and the effective time of measurement. Normal pulse polarography with varying pulse duration is put forward as a suitable technique to detect quasi-lability and to account for it. The Cd2+/EDTA system at low pH is used to illustrate the new classification and to test the existing theoretical treatments of kinetic effects. In the general case where we have both labile and quasi-labile complexes, the Brinkman-Los equation for pulse polarographic kinetic currents appears to be more satisfactory than the classical reaction layer theory. Starting from the dependence of limiting current on pulse width, a reasonable estimation can be made of the bulk concentrations of both types of complexes. © 1979 Elsevier Sequoia S.A.