Towards improving the electroanalytical speciation analysis of indium

Abstract

The geochemical fate of indium in natural waters is still poorly understood, while recent studies have pointed out a growing input of this trivalent element in the environment as a result of its utilisation in the manufacturing of high-technology products. Reliable and easy-handling analytical tools for indium speciation analysis are, then, required. In this work, we report the possibility of measuring the total and free indium concentrations in solution using two complementary electroanalytical techniques, SCP (Stripping chronopotentiometry) and AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) implemented with the TMF/RDE (Thin Mercury Film/Rotating Disk Electrode). Nanomolar limits of detection, i.e. 0.5 nM for SCP and 0.1 nM for AGNES, were obtained for both techniques in the experimental conditions used in this work and can be further improved enduring longer experiment times. We also verified that AGNES was able (i) to provide robust speciation data with the known In-oxalate systems and (ii) to elaborate indium binding isotherms in presence of humic acids extending over 4 decades of free indium concentrations. The development of electroanalytical techniques for indium speciation opens up new routes for using indium as a potential tracer for biogeochemical processes of trivalent elements in aquifers, e.g. metal binding to colloidal phases, adsorption onto (bio) surfaces, etc.

This work has been supported by the French National Research Agency through the national program “Investissements d’avenir” with the reference ANR-10-LABX-21-01/LABEX RESSOURCES21. We thank the contribution of Jérémy Gloux, Paco Iglesias and Mirella Dammous from University of Lorraine in the preliminary experimental work. Funding from the Spanish Ministry of Economy, Industry and Competitiveness MINECO, project CTM2016-78798 (EC, PPV, JG) is acknowledged. PPV thanks Generalitat de Catalunya for a doctoral FI-AGAUR fellowship.