Determination of cerium, gadolinium, dysprosium, erbium, and ytterbium

Concentrations of cerium, gadolinium, dysprosium, erbium, and ytterbium in thorium dioxides were measured by the isotope dilution methods. The electromagnetically enriched isotopes of these elements (140Ce, 155Gd, 164Dy, 167Er, 173Yb) were used as spike isotopes. After dissolution of the samples, known quantities of the spike solutions were added respectively, and rare earth elements were separated from the samples by thiocyanate-tri-n-butyl phosphate extraction and further divided into two groups (LaEu and GdLu) by reversed-phase chromatography. The isotopic compositions of the elements in the two groups were measured by a surface ionization type mass spectrometer (CEC 21-702B), and the concentrations of cerium, gadolinium, dysprosium, erbium, and ytterbium were calculated.