Sequential separation of light rare-earth elements, thorium and uranium by miniaturized extraction chromatography: Application to isotopic analyses of silicate rocks

A new method for the concomitant separation of the light rare-earth elements (LREEs), thorium and uranium is described, and applied to the determination of Nd-143/Nd-144 ratios, and concentrations of Sm, Nd, Th and U in silicate rocks, using isotope dilution and thermal ionization mass spectrometry. The proposed scheme is based on two recently introduced extraction chromatographic materials, referred to as TRU.Spec (TRansUranic-element Specific) and Ln.Spec. For most geological samples, the TRU.Spec 'resin' affords a straightforward separation of LREE, U and Th with high yield, good purity and satisfactory blank levels, on a single small (0.25 mi) column. Only Fe3+ was found to have detrimental effects on the LREE yields. For iron-rich samples, this troublesome interference was overcome by pretreatment on a shea cation exchange column. Besides, a tandem column arrangement with the Ln.Spec 'resin' enables the isolation of neodymium and samarium from bulk rock solutions be made in a single run. The validity of the method is illustrated by the measurement of Sm, Nd, Th and U concentrations along with Nd-143/Nd-144 ratios in 15 international standard reference materials.