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

Abstract

Competitive ligand exchange–adsorptive stripping voltammetry (CLE–AdSV) measures speciation of a metal M via a bulk exchange reaction with an adsorptive ligand L ad 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. The upper border of the kinetic detection window is defined by the requirement of equilibration before accumulation of the complex ML ad 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 ML ad and an excess of L ad over M. The adsorption of the surface-active complex ML ad is of a transient nature in the initial stage of the accumulation period, before the diffusive adsorption process approaches a steady-state nature.