Influence of adsorption on calibration curves in normal pulse polarography

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.