Issue 3, 2024

(LA)-MC-ICPMS/MS measurement of Sr radiogenic isotope ratios

Abstract

A prefiltering system made up of a double-Wien filter and a collision/reaction cell is included with the new Neoma MC-ICPMS/MS to reduce spectral interferences and allow high-precision isotope analyses. In the present study, we challenge these capabilities for measuring Sr isotopes. We first test the effect of different combinations of magnetic and electrostatic field values in the double-Wien filter on the transmission of a bandpass window that includes Sr isotopes and their reaction products. We next scrutinize the spectrum of ion products resulting from the introduction of N2O or SF6 to remove on-line Rb which interferes with Sr on the 87-mass unit. While N2O is the preferred reaction gas when using ICPMS/MS, we found that it reacts with Sr to create expected Sr16O products, but also 14N- and, most probably, 18O-based interfering products. By contrast, the introduction of SF6 generates a more resolved spectrum of F-based products, notably because F is mono-isotopic, but leads to a 50% reduction in signal intensity. Care must, however, be taken to measure 88SrF+ in a mass range free of the 32S19F316O+ interference. We then measure the 87SrF/86SrF ratio first in raw solutions of a suite of geological reference materials without prior Sr extraction and second in sintered in-house materials and natural solid samples using laser ablation. In the solution mode, no RbF+ is detectable and the sensitivity is ∼50 V ppm−1 for 88SrF+. The accurate measurements of the 87SrF/86SrF ratio of the geological reference materials are achieved with an uncertainty of 70 ppm (±2 SD), which is comparable with that typically obtained using MC-ICPMS with prior Sr extraction. In the laser ablation mode, the performance without SF6 of the Neoma for measuring Sr isotopes in homogeneous materials is roughly equivalent to that of the Neptune MC-ICPMS. With SF6, the Neoma MS/MS exhibits a sensitivity of ∼8 mV ppm−1 (based on 88SrF) and the measurement of the 87SrF/86SrF ratio has a short-term external precision of ∼0.0015 (±2 SD). Finally, an analysis of a heterogeneous material (a fossil tooth) reveals more well-resolved spatial variations of the 87SrF/86SrF ratio than of the 87Sr/86Sr ratio, likely thanks to the absence of 87RbF+.

Graphical abstract: (LA)-MC-ICPMS/MS measurement of Sr radiogenic isotope ratios

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
20 Oct 2023
Accepted
18 Jan 2024
First published
25 Jan 2024

J. Anal. At. Spectrom., 2024,39, 879-887

(LA)-MC-ICPMS/MS measurement of Sr radiogenic isotope ratios

P. Télouk and V. Balter, J. Anal. At. Spectrom., 2024, 39, 879 DOI: 10.1039/D3JA00358B

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