JRP CALL information
Supported By

European Commission

Short description of the work

The work at this second visit involved collecting experimental data for the estimation of complexation constants using capillary electrophoresis inductively coupled plasma mass spectrometry (CE-ICP-MS). Traditional methods of determining complexation constants involve potentiometry, spectrophotometry, solvent extraction, and calorimetry. These methods can be time consuming, labor intensive, and require work with larger quantities of materials than CE-ICP-MS. Efforts are being made to find additional techniques for determining these values while minimizing time and reducing material usage and hazardous and/or radioactive waste generation. Doing so helps to improve safety while also minimizing costs. CE-ICP-MS can provide estimates of complexation constants very quickly and uses minimal sample volumes. CE-ICP-MS can be used to relate electrophoretic mobilities of the metal-ligand complexes with ligand concentration; the electrophoretic mobilities can then be used to estimate relevant complexation constants.
For this second visit, we investigated the complexation constants between 2-hydroxy-2-methylbutyric acid (HMBA) and acetic acid, and actinides of various oxidation states. We also investigated the impact of solvent composition on these complexation constants. The solvent media explored were composed of water and methanol. CE-ICP-MS allows for the rapid, simultaneous detection of elements in solution matrices, such as the 10% and 30% (v/v) methanol media used in these experiments. The actinides used in the experiments were curium (III), plutonium (IV), neptunium (V), and uranium (VI).
In fully aqueous media, we were able to determine that mobilities of the actinides decreased with an increasing concentration of the ligand. This behavior indicates that the speciation of the each actinide is changing as the mobility is dependent on both the size and charge of the analyte. As the ligand concentration is increased, the prevalence of higher order species is increased, which in turn decreases the charge on the overall actinide-ligand complex as well as increasing the size of the complex. This same trend was also present in the mixed solvent media.
The main goal of this work is to use the experimental data collected at INE to estimate complexation constants in this mixed aqueous-methanol system. Experiments with varying ligand concentrations were repeated in aqueous solvent systems that included 10% and 30% methanol. The impact of methanol on complexation was investigated for both acetate and HMBA. The experimental results are currently being evaluated for the estimation of the stability constants, and will be reported in peer reviewed manuscripts in the future.

Main visitor contact data
Name: Kevin Bennett
Organisation: Washington State University

JRP Identification
JRP nr: TALI-C03-04
JRP title: Rapid Estimation of Actinide Complexation Constants in Mixed Solvent Media
JRP scope: Scope 1: Actinide separation chemistry

Visited Associated Pooled Facility
Visited APF during the stay: KIT-INE - Laboratories
Name of the APF Contact Person: Thorsten Schäfer

Other APF and organisation involved in the JRP
Other organisations involved: Washington State University (Dr. Sue Clark)
Other APF involved in the project:

Description of the work done at the associated pooled facility
Start date of the stay: 6/8/2015
End date of the stay: 7/24/2015
Quantity of access: 35
Access Unit: Days