HAL will be down for maintenance from Friday, June 10 at 4pm through Monday, June 13 at 9am. More information
Skip to Main content Skip to Navigation
Journal articles

Potassium isotopic composition of various samples using a dual-path collision cell-capable multiple-collector inductively coupled plasma mass spectrometer, Nu instruments Sapphire

Abstract : Mass-dependent K isotopic fractionations can be used to trace cosmochemical, geological, and biological processes such as evaporation/condensation, core formation, magmatic processes, weathering, and cellular metabolism. However, the application of stable K isotopes has been limited by major isobaric interferences from Ar, common on conventional multi-collector inductively-coupled-plasma mass-spectrometer (MC-ICP-MS), particularly for the low-K samples. Here, we present a set of high-precision K isotopic data acquired on terrestrial rocks, seawater, as well as a lunar meteorite using the recently released Nu Sapphire™ MC-ICP-MS that utilizes a collision cell to minimize Ar based interferences while maintaining remarkably high K sensitivity (≈ 2000 V/ppm). The influence of several parameters on the precision and accuracy of the K isotopic data has been evaluated, including total K concentration, K intensity mismatch between sample and standard, HNO3 molarity mismatch between sample and standard, and the presence of matrix elements. We found that the Nu Sapphire™ can be used to acquire precise and accurate data using as little as 125 ng of K, which represents an improvement by a factor 10 compared to what has been done on previous instruments. We present data for 23 previously analyzed samples; these data are highly consistent with literature values. On the other hand, accurate measurements are conditioned 1) to the close matching of sample and standard K intensities (a 1% mismatch creates a 0.02‰ offset on the 41K/39K ratio), and 2) to the absence of Ca (a Ca/K ratio of 1% creates a 0.069‰ offset on the 41K/39K ratio). In addition, Rb/K, Na/K, Ti/K and Cr/K ratio should also be maintained under 2.5% to avoid isotopic offset. We confirm the existence of significant mass-dependent K isotopic variations in terrestrial samples and that lunar rocks are isotopically heavier than terrestrial rocks. The incomparable sensitivity offered by the Nu Sapphire opens the possibility for high-precision K isotopic measurements across a wide range of samples for diverse applications.
Document type :
Journal articles
Complete list of metadata

https://hal-insu.archives-ouvertes.fr/insu-03353073
Contributor : Nathalie Pothier Connect in order to contact the contributor
Submitted on : Thursday, September 23, 2021 - 5:02:59 PM
Last modification on : Thursday, April 7, 2022 - 1:58:32 PM

Identifiers

Collections

Citation

Frédéric Moynier, Yan Hu, Kun Wang, Ye Zhao, Yvan Gérard, et al.. Potassium isotopic composition of various samples using a dual-path collision cell-capable multiple-collector inductively coupled plasma mass spectrometer, Nu instruments Sapphire. Chemical Geology, Elsevier, 2021, 571, pp.120144. ⟨10.1016/j.chemgeo.2021.120144⟩. ⟨insu-03353073⟩

Share

Metrics

Record views

13