Dynamic aspects of metal speciation by competitive ligand exchange–adsorptive stripping voltammetry (CLE–AdSV)

Competitive ligand exchange–adsorptive stripping voltammetry (CLE–AdSV) measures speciation of a metal M via a bulk exchange reaction with an adsorptive ligand Lad followed by electrochemical detection of the adsorbed metal complex. Thermodynamic aspects of the detection window of the technique are well understood. Here, we analyse the kinetic aspects including those involved with the adsorptive accumulation step. per border of the kinetic detection window is defined by the requirement of equilibration before accumulation of the complex MLad at the electrode surface. Analysis of the exchange step demonstrates that complexes with sample ligands that remain unaffected by the exchange step are generally nonlabile and do not contribute to the AdSV signal. Any residual free metal, however, does contribute to the accumulation process, but this contribution will be negligible in the usual situation of a sufficiently strong complex MLad and an excess of Lad over M. The adsorption of the surface-active complex MLad is of a transient nature in the initial stage of the accumulation period, before the diffusive adsorption process approaches a steady-state nature.