Stripping chronopotentiometry at scanned deposition potential (SSCP): Part 2. Determination of metal ion speciation parameters

Stripping chronopotentiometry at scanned deposition potential (SSCP) generates curves that are fundamentally different in form from classical polarographic waves. Still, despite their steeper slope and non-linear log plot, the shift in the SSCP half-wave deposition potential can be interpreted in a manner completely analogous to the DeFord–Hume treatment of polarographic waves. SSCP provides a reliable measure of metal speciation in the sample solution in the presence of simple ligands (i.e. those with non-distributed K and D values), even when there is relatively small ligand excess, and it is unaffected by induced metal adsorption. Data interpretation is not so straightforward for heterogeneous ligands: the presence of a range of metal complexes of slightly different stability and mobility flattens the SSCP wave as compared to the homogeneous case. The time dependent nature of the surface concentration of metal ion during deposition precludes straightforward rigorous interpretation of heterogeneous metal ion speciation.