Voltammetry as a Virtual Potentiometric Sensor in Modeling of a Metal‐Ligand System and Refinement of Stability Constants. Part 1. Polarographic and Glass Electrode Potentiometric Study of a Dynamic Cd‐Glycine System

Abstract

A mathematical conversion of data coming from nonequilibrium and dynamic voltammetric techniques (a direct current sampled (DC) and differential pulse (DP) polarography) into potentiometric sensor type of data is described and tested on a dynamic metal-ligand system. A combined experiment involving DCP, DPP and glass electrode potentiometry (GEP) was performed on a single solution sample containing a fixed [L T ] : [M T ] ratio (acid-base titration). Dedicated potentiometric software ESTA was successfully employed in the refinement operations performed on virtual potentiometric (VP) data obtained from DC and DP polarography. It was possible to refine stability constants either separately, from VP-DC or VP-DP, or simultaneously from any combination of VP-DC, VP-DP and GEP. The concept of VP-DC or VP-DP is reported for the first time and numerous documented and possible advantages are discussed. The proposed procedure can be easily utilized also by nonelectrochemists who are interested in, e.g., the ligand design strategies.

Measurements and Modeling To Determine the Reduction Potential of Uncomplexed Bi(III) in Nitrate Solutions for Application in Bi(III)-Ligand Equilibria Studies by Voltammetry

“…37,38 Since we wanted to work at moderate ionic strengths so that formation constants generated could have some application to the biological field, a nitrate background was chosen as the compromise between solubility of hydrolysis products and reversibility of the reduction process. The successful study of quasi-reversible systems had been previously been demonstrated, 39,40 however, as will be discussed, in this work it was found that the DC reduction waves could actually be considered as reversible when working in 0.25 -0.5 M nitrate solutions.…”

Voltammetry as a virtual potentiometric sensor in modelling of a metal–ligand system and refinement of stability constants. Part 4. An electrochemical study of NiII complexes with methylene diphosphonic acid

“…This implies that there is high likelihood that one might not be even aware about the presence of an error, hence E(M) must be determined with highest accuracy possible. It is however not always possible to attain an accurate E(M) value [23], or it might be unavailable from an experiment [19,21].…”

“…The change in the limiting diffusion current (I d ) can be as a result of the change in the diffusion coefficients of different labile metal complexes formed and/or due to the formation of polarographically inactive metal complexes. Cukrowski [19][20][21] has recently interpreted the expression below RT nF ln IðCÞ IðMÞ…”

“…The concept of virtual potential (E(virt)) was interpreted [19][20][21] as a thermodynamic potential of a virtual sensor or probe obtained from dynamic, non-equilibrium polarographic technique (each measurement, however, must be obtained after reaching a homogeneous equilibrium in the balk of a solution regardless of an experimental technique employed). This virtual potentiometric sensor must be sensitive to the change in the free metal ion concentration due to formation of metal complexes, but is metal ion non-specific due to the nature of a voltammetric experiment involving the reversible reduction of any polarographically active metal ion.…”

“…All the above-mentioned polarographic methods are characterised by a common requirement, namely, the need of potential E(M) at which uncomplexed metal ion is reduced. This is a severe limitation (parameter that carries a lot of uncertainty and is not always available from an experiment) that was eliminated by recently introduced a new concept of ''virtual'' potential [19][20][21]. Not only the need of E(M) was eliminated but also it was possible to employ ESTA in the refinement of non-equilibrium and dynamic data (after conversion to virtual potentials) either separately or together with real potentiometric data from GEP experiments.…”