An evaluation of a single-step extraction chromatography separation method for Sm-Nd isotope analysis of micro-samples of silicate rocks by high-sensitivity thermal ionization mass spectrometry

A single-step separation scheme is presented for Sm-Nd radiogenic isotope system on very small samples (1-3 mg) of silicate rock. This method is based on Eichrom (R) LN Spec chromatographic material and affords a straightforward separation of Sm-Nd from complex matrix with good purity and satisfactory blank levels, suitable for thermal ionization mass spectrometry (TIMS). This technique, characterized by high efficiency (single-step Sm-Nd separation) and high sensitivity (TIMS on NdO+ ion beam), is able to process rapidly (3-4 h), with low procedure blanks (<10 pg) and very small sample (1-3 mg). Replicate measurements by TIMS on Nd-143/Nd-144 ratios and Sm-Nd concentrations are presented for eleven international silicate rock reference materials, spanning a wide range of Sm-Nd contents and bulk compositions. The analytical results show a good agreement with recommended values within +/- 0.004% for the Nd-143/Nd-144 isotopic ratio and +/- 2% for Sm-Nd quantification at the 95% confidence level. It is noted that the uncertainty of this method is about 3 times larger than typical precision achievable with two-stage full separation followed by state-of-the-art conventional TIMS using Nd+ ion beams which require much larger amounts of Nd. Hence, our single-step separation followed by NdO+ ion beam technique is preferred to the analysis for microsamples. (C) 2011 Elsevier B.V. All rights reserved.