Scanned stripping chronopotentiometry of metal complexes: lability diagnosis and stability computation

A method is presented for analyzing the dynamic speciation features of metal complexes based on stripping chronopotentiometry at a scanned deposition potential (SSCP). The shift in the SSCP half-wave deposition potential, ΔEd,1/2, is straightforwardly related to the complex stability, K, irrespective of the degree of lability; the limiting wave height, τ*, quantifies the metal species accumulated in the electrode and thus depends on both the lability and mass transport properties of the metal complex species in solution. For complexes with a lower diffusion coefficient than the free metal ion, K calculated from ΔEd,1/2 will be the same as that derived from the relative τ* values so long as the system is fully labile. Discrepancies between ΔEd,1/2-derived and τ*-derived K values indicate loss of lability. We show that this approach is a sensitive indicator of lability, as illustrated by analysis of cadmium and lead binding by carboxylated nanospheres.