Study of CanUO2(CO3)3(4−2n)− complexes using CE-ICP-MS with polyetheretherketone (PEEK) capillaries

Abstract

The formation constants of Ca_nUO₂(CO₃)₃^(4−2n)− complexes were determined directly using capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS) in 0.1 M NaCl and at room temperature. Instead of conventional fused silica, polyetheretherketone (PEEK), a neutral organic material, was used as the capillary material to avoid interactions between uranyl and silica. Since PEEK is not optically transparent, a macrocyclic neutral complex, Ga-NOTA, was used to measure the electroosmotic flux directly by ICP-MS. The impact of the Joule effect was evaluated to control the temperature during electrophoresis. To alter the reversible interaction that arose from continuous use, a two-mode electrophoresis strategy was adopted. The observed mobilities of the samples showed a satisfactory correlation with the theoretical charge calculated from previous data (C. Shang and P. E. Reiller, Dalton Trans., 2020, 49, 466–481). The successive formation constants obtained in this work, log₁₀ K(CaUO₂(CO₃)₃²⁻) = 5.28 ± 0.39 and log₁₀ K(Ca₂UO₂(CO₃)₃(aq)) = 8.46 ± 0.67 in 0.1 M NaCl, were extrapolated to infinite dilution using the Davies equation, yielding log₁₀ β°(CaUO₂(CO₃)₃²⁻) = 27.12 ± 0.39 and log₁₀ β°(Ca₂UO₂(CO₃)₃(aq)) = 30.30 ± 0.67. These values are in excellent agreement with Shang and Reiller (C. Shang and P. E. Reiller, Dalton Trans., 2020, 49, 466–481). This further verifies the thermodynamic data available for these species and validates PEEK-based capillary electrophoresis for the measurement of thermodynamic constants of inorganic complexes in alkaline media.