Premium
Voltammetry as a Virtual Potentiometric Sensor in Modelling of a Metal/Ligand System and Refinement of Stability Constants. Part 2
Author(s) -
Cukrowski Ignacy,
Zhang Jian Min,
van Aswegen Anton
Publication year - 2004
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200490194
Subject(s) - potentiometric titration , chemistry , picolinic acid , polarography , ligand (biochemistry) , titration , stability constants of complexes , ionic strength , electroanalytical method , analytical chemistry (journal) , inorganic chemistry , metal , acid–base titration , base (topology) , electrode , chromatography , aqueous solution , organic chemistry , mathematical analysis , mathematics , biochemistry , receptor
Abstract A mathematical conversion of data from nonequilibrium and dynamic voltammetric techniques (direct‐current‐sampled (DC) and differential‐pulse (DP) polarography) into potentiometric, free‐metal‐ion sensor‐type data is described and employed in the study of Bi III complexes with the ligand picolinic acid (=pyridine‐2‐carboxylic acid) (labile and dynamic metal/ligand system). A novel procedure that allows evaluation of experimental data collected at very low pH values (acid‐base titration) is proposed. Software ESTA dedicated to potentiometry was successfully employed in the refinement operations performed with virtual potentiometric (VP) data obtained from DC and DP polarography, the latter being performed at fixed pH (ligand titration) as well as at fixed [L T ]/[M T ] ratio (acid‐base titration). It was possible to refine stability constants either separately from VP‐DC or VP‐DP, or simultaneously from any combination of VP‐DC and VP‐DP obtained from ligand and/or acid‐base titrations. The concept of VP‐DC or VP‐DP is employed for the first time in the study of an unknown Bi III /picolinic acid/OH system, and numerous documented and possible advantages are discussed. Five complexes of bismuth, ML, ML 2 , ML 3 , ML 4 , and ML 3 (OH) and their stability constants (as log β ) 7.48±0.01, 13.94±0.01, 18.10±0.04, 20.47±0.25, and 26.65±0.03, respectively, are reported at 0.5 M (Na,H)NO 3 ionic strength and T 298 K. The proposed procedure can be easily utilized also by non‐electrochemists who are interested in, e.g. , ligand‐design strategies.