Tellurium (Te) stable isotope measurements have the potential to serve as tracers of Te mobility and redox conditions in modern and ancient environments. Here, we present a method to measure Te isotope ratios by MC-ICP-MS utilizing a hydride generation system to efficiently deliver Te to the plasma, in combination with a 120 Te– 124 Te double spike. This approach allows for precise δ 130 Te/ 126 Te (2 σ : 0.09‰) measurements while using less than 8.75 ng of natural Te. Although hydride generation methods usually produce higher sensitivity than more conventional methods, for Te, the sensitivity is similar, on our instrument, to that achieved using a desolvating nebulizer. Nonetheless, hydride generation has an advantageous ability to exclude interfering elements such as Ba and allow analysis of samples without chemical separation of Te in some cases. We also demonstrate successfully a modified ion exchange procedure to separate various matrix components and isobaric interferences from Te in natural sediments. Analyses of multiple digestions of USGS standard reference materials, mine tailings, ancient sediments, and soils utilizing this approach show the largest spread in terrestrial Te isotopic composition to date (δ 130 Te/ 126 Te ∼ 1.21‰) and a lack of detectable mass-independent fractionation.
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High precision analysis of stable potassium (K) isotopes by the collision cell MC-ICP-MS “Sapphire” and a correction method for concentration mismatch
Stable potassium (K) isotopes (41K/39K) have shown great promise as novel chemical tracers for a wide range of bio-, geo-, and cosmo-chemical processes, but high precision stable K isotope analysis remains a challenge for plasma source mass spectrometry due to intense argon-related interferences produced directly from argon plasma. Here we provide an assessment on the analytical figures of merit of a new generation collision-cell equipped multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS), Sapphire from Nu Instruments, for K isotope analysis based on our extensive tests over a duration of ~8 months. Because use of helium and hydrogen as collision/reaction gases can reduce argon-related interferences to negligible levels at optimal flow rates, the collision-cell mode can operate at low mass resolution during K isotope analysis, providing >2 orders of magnitude higher K sensitivity (>1000 V per μg mL-1 K), as compared to the widely used “cold plasma” method, and the capability for direct 40K measurement. One challenge of the collision/reaction cell analysis on Sapphire is its higher susceptibility to matrix effects, requiring effective sample purification prior to analysis. Also, the collision-cell mode on Sapphire shows a pronounced effect associated with concentration (or ion intensity) mismatch between the sample and the bracketing standard during analysis, and this effect may not be fully eliminated through conventional concentration matching practice. Instead, we developed a correction method for this concentration/ion intensity mismatch effect. Our method reduces the burden to the operator and increases sample throughput. This method allows for accurate K isotope analysis with an intermediate precision of ≤0.05 ‰ (2SD) to be routinely achieved using the collision cell on Sapphire, representing a major advance to stable K isotope analysis.
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- Award ID(s):
- 1946945
- NSF-PAR ID:
- 10323842
- Date Published:
- Journal Name:
- Journal of Analytical Atomic Spectrometry
- ISSN:
- 0267-9477
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2JA00078D
