A novel extraction chromatography and MC-ICP-MS technique for rapid analysis of REE, Sc and Y: Revising CI-chondrite and Post-Archean Australian Shale (PAAS) abundances

Abstract

A new analytical protocol is introduced for rapid measurement of rare-earth elements (REE), Sc and Y in meteoritic and geological materials by multi-collection inductively coupled plasma mass spectrometry (MC-ICP-MS). A simple purification step was devised to reduce REE, Sc and Y abundances in commercial lithium metaborate (LiBO <inf>2</inf>) for low-blank flux fusion. Separation of the analytes from the rock matrix was achieved by using a single TODGA extraction chromatography step. A dynamic multi-collector cup configuration was developed to measure REE, Sc and Y using a desolvating nebulizer and standard-sample bracketing technique. To test the accuracy of this analytical protocol, we analyzed aliquots of USGS geological reference materials BHVO-1, BIR-1, BCR-2, PCC-1, W-2, G-2 and G-3, specifically selected to encompass a wide range of REE, Sc and Y concentrations and mineral compositions. Elemental abundances in reference materials are indistinguishable within analytical uncertainties from compilations of literature values analyzed by various ICP-MS techniques. The average external reproducibility on REE, Sc and Y concentrations (reported as RSD=100×standard deviation/average) was ~2% based on replicates of G-3. With the exception of PCC-1, which has low REE concentrations, adjustments for poly-atomic interferences and procedural blanks in the reference materials were negligible. In order to re-visit the terrestrial and cosmic abundances of REE, Sc and Y, aliquots of nine Post Archean Australian Shales (PAAS), Allende (CV-3), Tagish Lake (C2-ungrouped), Alais (CI1), Orgueil (CI1) and Ivuna (CI1) meteorites were measured using our new analytical procedure. The REE patterns of PAAS, normalized to the mean of CI-chondrites from this study, are smoother and show less dispersion compared with literature measurements. Eu/Eu ^*, σLREE/σHREE, and La/Sc ratios remain constant in these samples. The recommended PAAS composition based on these new measurements is (in μgg ^-1): Sc=15.89, Y=27.31, La=44.56, Ce=88.25, Pr=10.15, Nd=37.32, Sm=6.884, Eu=1.215, Gd=6.043, Tb=0.8914, Dy=5.325, Ho=1.052, Er=3.075, Tm=0.4510, Yb=3.012 and Lu=0.4386. The REE pattern in Allende is similar to group II-type Ca-Al-rich inclusions (CAIs) that typically show enrichment in light REE (LREE), depletion in heavy REE (HREE), and negative and positive anomalies for Eu and Tm, respectively. The REE in Tagish Lake and Alais do not show significant fractionations and closely resemble the relatively flat pattern observed in Orgueil. Based on eight high-precision multi-collection ICP-MS measurements of Orgueil (n=5), Ivuna (n=2) and Alais (n=1), we recommend a new CI-composition for REE, Sc and Y normalization and refine the cosmic abundances of these elements (in μgg ^-1): Sc=5.493, Y=1.395, La=0.2469, Ce=0.6321, Pr=0.0959, Nd=0.4854, Sm=0.1556, Eu=0.0599, Gd=0.2093, Tb=0.0378, Dy=0.2577, Ho=0.0554, Er=0.1667, Tm=0.0261, Yb=0.1694 and Lu=0.0256. © 2011 Elsevier B.V.