Determination of U(IV) and U(VI) by ion chromatography–inductively coupled plasma mass spectrometry and its application to kinetic studies

The ions normally formed by actinides in aqueous solutions by the oxidation states III–VI are M3+, M4+, MO2+ and MO22+, respectively. Oxidation state representatives such as Am3+, Th4+, NpO2+ and UO22+, which resist oxidation state changes, were used to investigate a method to separate the oxidised species (MO2+ and MO22+) from the reduced species (M3+ and M4+). With this method the hexavalent state of uranium could be separated from the tetravalent state of uranium in aqueous media in less than 8 min. Uranium concentrations down to 10−9 M could be analysed without changing the redox composition during the separation. The oxidation kinetics of the tetravalent uranium for different hydrochloric acid concentrations was investigated. The measurements showed good agreement with values found in the literature, although the uranium concentrations were one million times lower.