Free Eu3+ determination in natural waters
Résumé
The aim of this study was to develop an analytical method to determine free concentration of the rare earth element Europium in natural waters. Detection of Eu in solution using electroanalytical methods was performed by adsorptive cation stripping voltammetry after complexation with N-nitroso-N-phenylhydroxylamine (cupferron). Optimization of analytical parameters allowed us to detect nanomolar level of Eu(III) in solution.
To detect the amount of free Eu3+ in solution, we use the Donnan Membrane Technique (DMT) in which a natural solution (the “donor” side) is separated from a ligand-free (“acceptor”) solution by a cation-exchange membrane. This membrane allows only non-complexed cations to pass through it, and after a given equilibration time free metal concentration are equal in both sides. However, due to its high charge Eu3+ tends to get adsorbed onto the cation-exchange membrane. We analyzed solutions from different Eu3+ and Ca2+ (as background-ion) concentrations to determine physico-chemical conditions for which the method can be used. Results showed that 100 mM of Ca2+ prevented any adsorption of Eu from the solution. The optimized set-up was then used to determine Eu complexation in a Eu-fulvic acid solution.