Influence of anion-induced adsorption on half-wave potentials and other polarographic characteristics

Previously observed differences between accepted and apparent polarographic stability constants for some systems containing adsorbable ligands have been confirmed by d.c. and a.c. polarography. The same discrepancy is not observed with amalgam potentiometry. This behaviour is believed to result from anion-induced adsorption of the depolarizer and at least partial subsequent reduction in the adsorbed state. Both the d.c. and a.c. polarographic behaviour of such systems has been shown to be characterized by subtle departures from normal Nernstian behaviour although not in the sense usually attributed to kinetic irreversibility. Detailed study of the lead(II)-bromide and-iodide and some thallium(I) systems are reported. Maxima, depletion and other unusual effects also attributable to specific adsorption of the depolarizer are evident.