Interferences and Matrix Effects on Iron Isotopic Composition Measurements by 57Fe-58Fe Double-Spike Multi-Collector Inductively Coupled Plasma Mass Spectrometry; the Importance of Calcium and Aluminum Interferences

F Lacan,R Freydier,J Chmeleff,L Artigue,J K Klar,C Pradoux

doi:10.3389/fenvc.2021.692025

Abstract

Multi-collector inductively coupled plasma mass spectrometers (MC-ICPMS) are widely used for Fe isotope measurements. The latter may be perturbed by interferences (notably from Cr and Ni) and matrix effects (notably from major elements), caused by elements remaining in the samples after purification. We quantified some of these perturbations and our ability to correct them whenever possible, using Thermo Neptune and Neptune Plus MC-ICPMS with a 57-58Fe double-spike mass bias correction. 54Cr and 58Ni isobaric interference corrections were found to be extremely efficient up to Cr/Fe=0.12 and Ni/Fe=0.04 (g/g natural Fe). Matrix effects were found negligible up to at least Na/Fe=175, Mg/Fe=10, K/Fe=1.5, and Mo/Fe=75 (g/g natural Fe). 28Si2+ interference was found negligible up to Si/Fe=50. Finally, we found that calcium and aluminum could cause significant interferences (e.g., 40Ca16O and 27Al2+), for Ca/Fe ≥ 2.5 and Al/Fe ≥ 2.5. The perturbation intensity relative to the Ca/Fe ratio was found dependent on the measurement conditions (plateau width). While working with samples with potentially high calcium or aluminum contents (such as calcite minerals or tests, bones and teeth, or marine samples and crustal rocks), we recommend to carefully take into account Ca and Al while tuning the instrument and checking the measurement accuracy with isotopic standards (i.e., doping the isotopic standard with Ca and Al levels comparable to those of the samples).

Highlights

Iron isotopic compositions are nowadays widely used in Earth and planetary sciences, environmental research, and in biological and medical research (Beard and Johnson, 2004; Abadie et al, 2017; Albarède et al, 2017; Dauphas et al, 2017)
While samples are usually purified before Fe isotopic composition MC-ICPMS analysis, some elements may remain in the purified samples at significant concentrations, in some circumstances
We have tested the effect of the following perturbations on the accuracy of the Fe isotopic composition measurement with a Neptune and a Neptune Plus MC-ICPMS, using a 58Fe-57Fe double-spike mass bias correction:

Summary

Introduction

Iron isotopic compositions are nowadays widely used in Earth and planetary sciences, environmental research, and in biological and medical research (Beard and Johnson, 2004; Abadie et al, 2017; Albarède et al, 2017; Dauphas et al, 2017). The present work presents for the first time a study of the impact of Cr, Ni, Ca, Si, and Al interferences and Na, Mg, Ca, K, and Mo matrix effects on iron isotope measurements using Thermo-Scientific Neptune and Neptune Plus MC-ICPMS with desolvation and a mass bias correction with a 57Fe-58Fe double-spike.

Results

Conclusion