ELSEVIER Chemical Geology 129 (1996) 201-208 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON CHEMICAL GEOLOGY ,K‘““,Nc ISOTOPE GEOSCIENCE Separation of Ce from other rare-earth elements with application to Sm-Nd and La-Ce chronometry M. RehkAmper * ‘l, M. G’sirtner 2, S.J.G. Galer, S.L. Goldstein Mar-Planck-lnstitut~r Chemie, Abteilung Geochemie, Postfach 3060, D-55020 Mainz, Germany Received 21 August 1994; accepted 13 September 1995 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR Abstract The rare-earth element (REE) pairs Sm-Nd and La-Ce include three radioactive decay systems that are used in geo- and cosmochemistry for dating and tracer studies. Efficient chemical separation techniques are required prior to isotopic analysis of Ce and Nd. Matrix elements with low work functions must be removed from samples, since they can have a severe effect on ionization efficiency; isobars from other elements must also be eliminated in order to reduce interference corrections. These steps are particularly important for high-precision measurements, such as for 14’Nd/ IaNd or Ce isotope analyses. Here we report a simple but highly efficient two-phase micro-extraction technique for the separation of Ce from the other REE. The procedure involves oxidation of Ce3+ to Ce4+ using a solution of NaBrO, in nitric acid and extraction of the tetravalent species into an organic solvent containing HDEHP. The other lanthanides remain trivalent and are thus left in the aqueous nitric acid phase. The method is characterized by high elemental yields, excellent separation factors and low reagent blank contributions. The solvent extraction method has been successfully used for (1) cleaning of Nd from Ce contamination and (2) the isolation of Ce from other REE for mass spectrometry. Isotopic analyses of the extracted samples showed minimal isobaric interferences, demonstrating that the technique achieves separation factors superior to standard procedures. 1. Introduction The rare-earth elements (REE) La, Ce, Nd and Sm include three radiogenic decay systems that are particularly useful in geo- and cosmochronology and for geochemical tracer studies. Of these the l4 Sm- 143Nd a-decay scheme is most commonly used. The now-extinct primordial nuclide 14%rn o-decays to * Corresponding author, ’ Department of Geological Sciences, The University of Michi- gan, Ann Arbor, MI 48103-1063, USA. ’ Institut fiir Anorganische Chetnie, Universitst Bern, Freie Stra8e 3, CH-3012 Bern, !;witzerIand. 14*Nd with a half-life of 103 Ma, allowing the study of processes that took place in the early history of the solar system (Scheinin et al., 1974) and possibly the Earth (Goldstein and Galer, 1992; Harper and Jacobsen, 1992). Over the past few years, the 13*La- 13*Ce isotope system has gained increasing impor- tance in geochemistry (e.g., Tanaka and Masuda, 1982; Dickin, 1987; Makishima and Nakamura, 1991). Efficient chemical separation procedures are a necessity prior to most isotopic analyses by mass spectrometry. Firstly, the element of interest has to be separated from the geological matrix; secondly, isobars from other elements which interfere with the 0009-2541/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0009-2541(95)00143-3