Measuring the isotopic composition of trace elements in zircon: application to radiogenic molybdenum

TL;DR

This paper presents advanced techniques for measuring trace molybdenum isotopic compositions in zircon, overcoming interference issues, and achieving high precision with minimal sample quantities, useful for studying nuclear decays in geological samples.

Contribution

Developed improved digestion, separation, and data analysis methods for precise Mo isotope measurement in zircon using MC-ICPMS, with enhanced efficiency and lower detection limits.

Findings

Achieved <0.1 permil precision on Mo isotopes with <50 ng Mo recovered.

Reduced zirconium interference by over 9 orders of magnitude.

Demonstrated applicability to other atomic species in trace analysis.

Abstract

Techniques have been developed to measure the isotopic composition of trace elements from matrices predominantly consisting of interfering isotopes. These techniques have been applied to measuring mass-independent fractionation of molybdenum in ancient zircon samples due to nuclear decays. Improvements to the digestion of large zircon samples and the ion exchange chemistry required to separate trace molybdenum from zirconium silicate are presented. The efficacy of TEVA ion exchange resin as a replacement for anion resin to improve separation efficiency and chemistry blank was studied. An algorithm was established to improve background, interference and mass bias corrections for the data analysis of Mo by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). This enabled the isotopic composition measurement of $<$50 ng of Mo recovered from 500 mg ZrSiO$_4$ by reducing the Zr content by $>$9 orders of magnitude while retaining 63% of the Mo. With 5 ng of Zr still remaining, novel data analysis techniques enabled $<$0.1 permil precision on each Mo isotope. The relevance of this technique to extracting other atomic species is also discussed.