Optimum conditions for polarographic studies of mixed‐ligand complex formation

Abstract

Some characteristics of bi-ligand systems, important for the design and performance of studies on mixed-ligand complex formation, are given. The problem of the optimum ligand concentration is discussed using published results. In the experimental work the concentration range of the stronger complexant (at a constant level of the weaker) seems to be critical. The measurements should start under conditions where the increase in the half-wave potential shift (with respect to the situation in the presence of only the weaker ligand) is virtually absent and finish at concentrations where it is pronounced. Small changes at the beginning reflect the 'contribution' of ternary species to the composite signal, whereas the big shifts at higher concentrations are mainly produced by simple species with only a minor contribution from mixed-ligand complexes.

ΔEp vs. pH Plot as a Source of Information in Polarographic Studies of Kinetically Labile Metal Complexes at a Constant Ligand to Metal Ratio

“…Only in situations in which complexation with OH À starts at pH values at which virtually complete (first) ligand is present in its deprotonated form the system behaves as if one complexant is kept at a constant level whereas concentration of the other is gradually increased. Under such conditions, previously described treatment [3,4,6] could perhaps be applied at higher pH values after calculation of b p constants from the experimental points corresponding to more acidic solutions (before the second rising part of the curve) and their introduction in the corresponding program. An example is presented in Figure 10 where peak potential shift as a function of pH is given for Cd 2 -Ac À -OH À system at several different concentrations of the total dissolved acetate.…”

Voltammetric determination of trace mercury in concentrated chloride media using polymer-film electrodes modified with polyammonium macrocyclic receptors

“…Then, plots of DE p vs. log[Cl 2 ] must provide a straight line with slope 2.303RTy/mnF. For our purposes, however it is convenient to introduce, following Zelic, 43 the difference between the peak potential shifts of solutions containing a constant amount of the macrocyclic ligand and increasing concentrations of Cl 2 , and Cl 2 solutions in the absence of macrocyclic ligand. The values of these new potential shift, D(DE p ), must verify:…”

An analysis of distinguishing composite dissolved metal–ligand systems measurable by stripping voltammetry

“…In contrast, theoretical calculations based on the knowledge of simpler systems, analyses of factors affecting the recognition of ternary complexes, and the reviews about particular ligand's behaviour in the environment (e.g. [48][49][50][51][52]) can be found. Mixed metal-ligand complexes were studied in order to improve the sensitivity of the voltammetry as electroanalytical method by multiple enhancement of metal-mixed ligands complexes adsorption onto mercury drop electrode and formation of metal-mixed ligands-surface complex, known as synergetic adsorption [53][54][55].…”