Stripping chronopotentiometry at scanned deposition potential (SSCP). Part 8. Metal speciation analysis in gels

In case of a finite negative Donnan potential difference, ΨD, metal speciation in a gel is significantly altered as compared to that in the surrounding aqueous medium. For anionic gels (e.g., typical biogels), ΨD leads to enhanced concentrations of positively charged species within the gel, and reduced concentrations of negatively charged ones. Thus both the absolute concentrations and the ratios of species are altered. Stripping chronopotentiometry at scanned deposition potential is shown to provide a reliable measure of the stability and lability of metal species in gels. Results are reported for labile, quasilabile and inert metal–ligand systems. Failure to take into account the Donnan partitioning leads to erroneous interpretations on the distribution and lability of species within the gel phase. Translation of the speciation measured within the gel to that in the surrounding medium is involved for chemically heterogeneous systems, e.g., natural waters. The results are of importance for interpretation of analytical signals from gel-integrated sensors and for understanding the behaviour of the different metal species in biogels.