Measurement of metals Using DGT:impact of ionic strength and kinetics of dissociation of complexes in the resin domain

Puy, Jaume and Galceran, Josep and Cruz-González, Sara and David, Calin A. and Uribe, Ramiro and Lin, Chun and Zhang, Hao and Davison, William (2014) Measurement of metals Using DGT:impact of ionic strength and kinetics of dissociation of complexes in the resin domain. Analytical Chemistry, 86 (15). pp. 7740-7748. ISSN 0003-2700

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Abstract

As the measurement of metals by DGT (diffusion gradients in thin films) in low salinity media has been controversial, a thorough study of the impact of ionic strength (I) is timely. DGT accumulations of Cd, Co, and Ni in the presence of NTA at pH 7.5 with I in the range from 10–4 to 0.5 M were obtained. An observed decrease in the metal accumulation as the ionic strength of the system decreased is partially explained by the electrostatic repulsion between the negatively charged resin domain and the dominant negatively charged complex species M–NTA. This electrostatic effect reduces the complex penetration into the resin domain, especially for nonlabile complexes, which do not fully dissociate in the gel domain. Analytical expressions, based on the Donnan model, were able to quantify these electrostatic effects. Additionally, the data indicate that the kinetic dissociation constant of M–NTA complexes in the resin layer is higher than Eigen predictions, suggesting a ligand-assisted dissociation mechanism. As the ionic strength decreases, the rate of reaction in the resin layer decreases due to the repulsion between the negatively charged resin sites and the complex species. This decrease contributes to the decrease in metal accumulation. These novel, previously unconsidered, effects of ionic strength and the ligand-assisted dissociation mechanism in the resin domain will affect DGT measurements made in freshwaters and soils.

Item Type:
Journal Article
Journal or Publication Title:
Analytical Chemistry
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/1600/1602
Subjects:
ID Code:
82447
Deposited By:
Deposited On:
25 Oct 2016 13:14
Refereed?:
Yes
Published?:
Published
Last Modified:
04 Jun 2020 03:41