Precise isotopic measurements of sub-nanogram Nd of standard reference material by thermal ionization mass spectrometry using the NdO+ technique

摘要

The Sm-Nd isotopic system, one of the important techniques for dating and geochemical tracing, has been widely used in geosciences. Precise and accurate measurements of Nd isotopic ratios are more difficult to achieve for microsamples that contain less than 50 ng Nd, when routine Nd+ technique is applied on thermal ionization mass spectrometer (TIMS). Compared to Nd+ technique, the NdO+ technique, owing to more efficient ionization, is a better choice for high precision measurements of Nd isotopic ratios of micro- or low-content samples. This study presents measurement results of sub-nanogram size samples of standard reference solution and rock-powder using NdO+ technique on the latest TIMS (GV product IsoProbe-T). Sixteen rock-powder references and four reference solutions were measured both by NdO+ and Nd+ techniques for an evaluation of accuracy and precision of measurements obtained by the NdO+ technique. Results show that analytical precision and reproducibility of NdO+ measurements of sub-nanogram Nd is comparable with those obtained by the Nd+ measurements of samples containing 200 ng Nd. Internal precision of the Nd-143/Nd-144 ratios achieved with both techniques is better than 0.003%. Our results show that the microsample NdO+ technique is a very promising method for high resolution Sm-Nd geochronology and isotopic tracing. (C) 2007 Elsevier B.V. All rights reserved.