Investigation of the Interaction of Gadolinium with Several Organic Ligands and Humic Acid by Ligand Competition Using 4-(2-Pyridylazo)-Resorcinol (PAR)

Spencer Steinberg,Luis Becerra-Hernandez,Vernon Hodge

doi:10.3390/environments7090069

Spencer Steinberg, Luis Becerra-Hernandez + Show 1 more

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https://doi.org/10.3390/environments7090069

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Journal: Environments	Publication Date: Sep 3, 2020
Citations: 2	License type: CC BY 4.0

Affiliation: University of Nevada, Las Vegas

Abstract

Gd3+ forms a strongly colored complex with 4-(2-pyridylazo)-resorcinol (PAR) in aqueous solutions. We characterized the Gd3+-PAR complex in order to use it as a probe of Gd3+ speciation in the presence of environmentally relevant ligands. The formation of the Gd3+-PAR complex was investigated from pH 5 to 8 in the presence of excess PAR. The absorbance of the Gd3+-PAR complex dramatically increased from pH 5 to 8 and application of the method of continuous variation indicates that the complex was primarily 1:2 Gd(PAR)2 at pH 8. Stability constants for Gd3+ with other ligands can be quantified by competitive displacement of the PAR ligand. To establish the viability of this approach, we measured the stability constants between Gd3+ and several organic acids and carbonate. Our measurements show reasonable agreement with the literature values. We used the competitive displacement approach to establish that humic acids can competitively displace PAR from the Gd(PAR)2 complex.

Highlights

Due to the use of Gd3+ in magnetic resonance imaging and manufacturing, large quantities of gadolinium have been released into the environment [1,2,3]
Most of the measurements were conducted at pH 8, where the response was 3+ concentration the absorbance favorable at 510 nm with total indicates that these conditions and hydrolysis wasGd not extensive due to the presence of PAR
We have demonstrated that through a competitive ligand methodology using PAR, it is possible to measure stability constants for various ligands of potential environmental importance

Summary

Introduction

Due to the use of Gd3+ in magnetic resonance imaging and manufacturing, large quantities of gadolinium have been released into the environment [1,2,3]. Gd3+ can be extremely toxic under some circumstances, and an investigation of its chemistry in the environment is warranted. The goal of this work was to develop a method that can probe the interaction of Gd3+ with environmentally important ligands including organic acids and humic materials. It is important to gauge the impact of potentially competitive side reactions such as hydrolysis on the formation of the PAR complex. These experiments were conducted with Gd3+ at micro-molar (uM) concentrations

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