Voltammetry as Virtual Potentiometric Sensor in Modelling of a Metal/Ligand System and Refinement of Stability Constants. Part 5

Abstract

The concept of virtual potential (employed here in modelling operations), a unique experimental setup designed and built in our laboratories, and new regression equations derived for nonlinear fitting of quasi‐reversible direct‐current polarograms were combined with the existing rigorous treatment and refinement of polarographic data to establish reliable metal/ligand models and accurate stability constants for the lead(II)/glycine/OH− and lead(II)/sarcosine/OH− systems (sarcosine = N‐methylglycine). In the case of glycine, the complexes [M(HL)], [ML], [ML2], and [ML3] were identified, and their stability constants (as log β) were established to be 10.51 ± 0.06, 4.58 ± 0.02, 7.19 ± 0.10, and 9.27 ± 0.02, respectively, the complex [ML3] being reported here for the first time (Table 2). The system with sarcosine involving [M(HL)], [ML], [ML2], [ML3], and [ML2(OH)2], with the stability constants (as log β) 11.01 ± 0.04, 4.18 ± 0.03, 7.23 ± 0.03, 9.1 ± 0.3, and 15.97 ± 0.07, respectively, is reported for the first time (Table 3). The log K1 value for PbII with sarcosine is a fraction of a log unit smaller when compared with the PbII complex with glycine, in agreement with the literature data for CuII, NiII, and ZnII showing the same trend for these two ligands. The proposed nonlinear curve‐fitting operations expand the applicability of polarography to study reliably and conveniently quasi‐reversible, on the polarographic time scale, metal/ligand systems (systems with involved heterogeneous kinetics).

A Novel Approach to Monitoring of the Diffusion Junction Potential in Speciation Studies by Polarography Under very Acidic Conditions. Part I: The Reversible Cd(II)‐Picolinic Acid System

“…Polarographic experiments were carried out using an automated setup described previously [14]. A jacketed titration vessel was used and the temperature maintained at 25.0 ± 0.1 o C u s i n g a w a t e r b a t h w i t h a L a b c o n CPE100 temperature controller and the temperature of the sample solutions were monitored using a Metrohm thermocouple.…”

Adsorption of domoic acid to marine sediments and clays

“…Many amino acids are also excellent ligands for transition metals (stability constants on the order of 10 8 -10 12 ). [21][22][23][24][25][26][27] The coincidence of these properties makes it difficult to predict the adsorptive behavior of amino acids in complex environmental systems, where their behavior may be governed by direct adsorption to surfaces or by the adsorption of a transition metal-amino acid complex. 23,[28][29][30][31] In this study, we have determined K d for domoic acid with several different marine particulates and clays, including Gulf of Mexico sediment, Bread and Butter Creek sediment (Georgetown, SC, USA), Santa Barbara Basin sediment, kaolinite, kaolin, montmorillonite, and diatomaceous earth.…”