Investigation of the Electrophoretic Mobility of the Actinides Th, U, Np, Pu, and Am in Different Oxidation States

The electrophoretic mobilities (mu(e)) of the actinides Th and U-Am in different oxidation states (prepared in 1 M HCl and 1 M HClO4) have been determined by capillary electrophoresis (CE)-inductively coupled plasma mass spectrometry (ICPMS) using 1 M acetic acid as the background electrolyte, which has proven to provide an excellent setup for trace analysis at environmentally relevant concentrations (1 x 10(-9) M). The values are independent of the respective acid solution. The mu(e) of the Pu oxidation states +III to +VI have been measured. They agree with both the available literature data and the redox-stable analogues (Eu(III), Th(IV), Np(V), U(VI)) that have also been investigated. The trend in the mu(e) for the actinides U-Pu was found to be An(III) > An(VI) > An(V) > An(IV). The mu e values of Am(III) (mu(e)(Am(III)) = 3.86 x 10(-4) cm(2)/(Vs)), U(IV) (mu(e)(U(IV)) = 0.34 x 10(-4) cm(2)/(Vs)), and U(VI) (mu(e)(U(VI)) = 1.51 x 10(-4) cm(2)/(Vs)) have been measured for the first time under these experimental conditions. Furthermore, the measured mu(e) values show systematic trends that can be rationalized on the basis of the calculated species distribution of the actinides in 1 M acetic acid and the corresponding average effective charges (q(eff)).