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Chromatography purification of Rb for accurate isotopic analysis by MC-ICPMS: a comparison between AMP-PAN, cation-exchange, and Sr resins

Nie, Nicole X. and Dauphas, Nicolas and Hopp, Timo and Hu, Justin Y. and Zhang, Zhe J. and Yokochi, Reika and Ireland, Thomas J. and Tissot, François L. H. (2021) Chromatography purification of Rb for accurate isotopic analysis by MC-ICPMS: a comparison between AMP-PAN, cation-exchange, and Sr resins. Journal of Analytical Atomic Spectrometry, 36 (12). pp. 2588-2602. ISSN 0267-9477. doi:10.1039/d1ja00268f. https://resolver.caltech.edu/CaltechAUTHORS:20211015-162630777

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Abstract

The isotopic compositions of alkali metal elements are powerful tracers of various geological processes. Coupled K and Rb isotopic studies can potentially yield new clues on the mechanisms responsible for the depletions in moderately volatile elements in planetary objects, global surface geochemical cycles, and mechanistic aspects of water–rock interactions. Rubidium isotopic studies have however been hampered by difficulties in purifying Rb from rocks, notably due to its similar chemical behavior to K. Here we characterize the properties of three different types of resins (AMP-PAN resin; AG50W-X8 and AG50W-X12 cation-exchange resins; Sr resin) for Rb and K purification. We show that AMP-PAN resin and Sr resin can readily separate Rb from K and other matrix elements. However, AMP-PAN resin has a high Rb blank (∼80 ng) and is cumbersome to use, which limits its applicability. For cation resins, we test the effects of column length, acid molarity, temperature, pressure drop (flow rate), and resin cross-linkage on the Rb separation using a Fluoropolymer Pneumatic Liquid Chromatography (FPLC) unit built in our laboratory. Increasing column length or resin cross-linkage has a positive effect on the separation, while increasing acid molarity, temperature, or pressure drop (flow rate) has negative impacts. Gravity-driven cation-exchange resin columns fail to cleanly separate Rb from K, but an AG50W-X12 resin column of 150 cm length and 0.16 cm inner diameter installed on a FPLC unit can cleanly separate Rb from K. We separated Rb from synthetic and natural rock samples using three different purification schemes designed based on the three types of resins, and measured the Rb isotopic compositions of the Rb separates by MC-ICPMS. The three methods yielded consistent results, demonstrating the efficacy of our Rb separation and the accuracy of our Rb isotopic analyses. The Rb isotopic compositions of several geostandards were analyzed (BCR-2, BHVO-2, BE-N, AGV-2, GS-N, G-3, and G-A), which can be used in future studies for ground-truthing methodologies used for studying natural samples. Among the three methods, the Sr resin method is the most straightforward for purifying Rb and K simultaneously, and measuring their isotopic compositions in natural samples.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1039/d1ja00268fDOIArticle
ORCID:
AuthorORCID
Nie, Nicole X.0000-0003-1828-5377
Dauphas, Nicolas0000-0002-1330-2038
Hopp, Timo0000-0002-4056-5431
Hu, Justin Y.0000-0002-3705-8148
Yokochi, Reika0000-0002-8756-142X
Tissot, François L. H.0000-0001-6622-2907
Additional Information:© The Royal Society of Chemistry 2021. Submitted 29 Jul 2021. Accepted 06 Oct 2021. First published 06 Oct 2021. This work was supported by a NASA NESSF fellowship (NNX15AQ97H), a Carnegie postdoctoral fellowship, and a Carnegie Postdoc × Postdoc (P2) seed grant to NXN, NASA grants NNX17AE86G, NNX17AE87G, 80NSSC17K0744, 80NSSC20K0821, and NSF grant EAR-2001098 to ND. There are no conflicts to declare.
Funders:
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX15AQ97H
Carnegie Institution for ScienceUNSPECIFIED
NASANNX17AE86G
NASANNX17AE87G
NASA80NSSC17K0744
NASA80NSSC20K0821
NSFEAR-2001098
Issue or Number:12
DOI:10.1039/d1ja00268f
Record Number:CaltechAUTHORS:20211015-162630777
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20211015-162630777
Official Citation:Chromatography purification of Rb for accurate isotopic analysis by MC-ICPMS: a comparison between AMP-PAN, cation-exchange, and Sr resins. J. Anal. At. Spectrom., 2021, 36, 2588-2602; DOI: 10.1039/d1ja00268f
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111465
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:18 Oct 2021 17:55
Last Modified:01 Dec 2021 22:18

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