Actinide oxalate complexes formation as a function of temperature by capillary electrophoresis coupled with inductively coupled plasma mass spectrometry

Complexation of various actinides (U(VI), Np(V), Pu(V), Am(III)) by oxalato ligand was studied by capillary electrophoresis (ICPMS detection) in 0.1 mol L–1 NaClO4 ionic strength solutions at various temperatures (15, 25, 35, 45 and 55 ℃). For each solution a unique peak was observed as a result of a fast equilibrium between the free ions and the complexes (labile systems). The results confirmed the formation of the 1:1, 1:2 and 1:3 complexes for U(VI) and Am(III); the formation of the 1:1 and 1:2 complexes for Np(V) and the formation of only 1 complex for Pu(V). For each complex, the thermodynamic parameters (the Gibbs energy ΔrG(T), the molar entropy change ΔrS(T) and the molar enthalpy change ΔrH(T0)) were fitted to the experimental data. The effect of the ionic medium was treated using the specific ion interaction theory and the thermodynamic parameters at zero ionic strength were compared to previously published data.