Problems and Solutions when Quantifying Nitrogen in Silicate and Oxide Minerals and Glasses Using Electron Probe Microanalysis

Abstract

With growing interest in the Earth's deep nitrogen cycle, electron probe microanalysis is increasingly used to quantify nitrogen in minerals and glasses. However, measuring nitrogen by electron microprobe comes with challenges, including beam sensitivity and differences in peak and background shapes between sample and reference materials. This study provides a robust analytical protocol to addresses these issues. We gathered mineral and glass reference materials with known nitrogen mass fractions from previous work, and synthesised additional glasses with nitrogen quantified independently by gas-source mass spectrometry. Our method uses nitrides as calibration materials because of their beam stability and high nitrogen mass fraction. We assess peak shapes to implement an area-peak factor correction, and account for curved backgrounds using a four-point background correction. Importantly, we describe how to estimate uncertainties on both background and area-peak factor corrections, which is required to assess detection limits but has been largely overlooked in previous studies. Our method yields nitrogen mass fractions within uncertainty for five out of seven reference materials, with two exceptions highlighting the need for further refinement. We provide Python code for applying the corrections and calculating uncertainties, allowing our method to be implemented by any researcher with access to an electron microprobe laboratory.