Issue 7, 2024

High-precision stable isotope measurements of tungsten and molybdenum in single sample aliquots combined with optimized separation for mixed double spikes

Abstract

A key driver to develop stable tungsten (W) isotope geochemistry is its unique relationship with molybdenum (Mo). Here, we establish a combined double-spike (DS) method for W (180W–184W spike) and Mo (97Mo–100Mo spike) to perform simple, efficient, and robust isotope measurements of these two chemically analogous elements in single sample aliquots. Based on previous column chemistry, we optimized two-stage anion-exchange procedures to remove matrix elements, particularly the critical interference of Ta and Hf on 180W, and to collect sharply separated W and Mo fractions. The obtained recoveries are quantitative for both elements, and their purities are sufficiently high to achieve high-precision measurements comparable to previous DS measurements of individual elements. The reproducibility of our isotope measurements for in-house standard solutions (2SD) was ±0.02‰ for δ186W and ±0.03‰ for δ98Mo. We applied our method to 27 geological reference materials including 10 igneous rocks (AGV-2, JA-3, JR-1, JB-1, JB-1a, JB-2, JB-3, W-2a, TDB-1, and WGB-1), 9 sediments (Nod-A-1, Nod-P-1, JMn-1, JMS-1, JMS-2, CRM7302-a, HISS-1, MESS-4, and PAC-3), and 8 sedimentary and metasedimentary rocks (SDC-1, SDO-1, SBC-1, SCO-1, SCO-2, JSL-1, JSL-2, and IOC-1) to produce a comprehensive data set. The data set confirmed the accuracy of our measurements and expanded the reference materials available for interlaboratory comparisons of δ186W and δ98Mo. The data set also indicates potential pitfalls in sample preparations for particular sample types and shows several variations of W and Mo isotopes possibly related to low-/high-temperature geochemical processes. Our new method, plus the reference data set, will facilitate the development of stable isotope geochemistry for W and Mo.

Graphical abstract: High-precision stable isotope measurements of tungsten and molybdenum in single sample aliquots combined with optimized separation for mixed double spikes

Supplementary files

Article information

Article type
Paper
Submitted
17 fev 2024
Accepted
24 apr 2024
First published
30 apr 2024

J. Anal. At. Spectrom., 2024,39, 1759-1777

High-precision stable isotope measurements of tungsten and molybdenum in single sample aliquots combined with optimized separation for mixed double spikes

T. Kashiwabara, Y. Fukami, S. Kubo, A. Watakabe, M. Kurisu, S. Tokeshi, T. Iizuka and K. Suzuki, J. Anal. At. Spectrom., 2024, 39, 1759 DOI: 10.1039/D4JA00059E

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