Interference-free electron probe micro-analysis of bromine in halogen-bearing minerals and glasses: high-resolution measurements and quantitative elemental mapping

Abstract

Previous attempts to measure Br in minerals and glasses via electron probe micro-analyzers (EPMA) required interference corrections via calibration curves in order to account for Al X-ray overlap with the Br L_β X-ray signal. We present a new approach for using EPMA for Br quantification in halogen-bearing minerals and glasses by measuring the interference-free Br K_α X-ray signal (11.909 keV), using a lithium fluoride (LiF) diffracting crystal. A set of Br-doped glasses as well as Cl- and Br-bearing scapolite-group minerals that were previously characterized by SIMS, INAA, LAICPMS, EPMA, and the Noble Gas Method, is compared to new EPMA measurements. Bromine concentrations in the tested samples range from ∼10 to ∼3500 μg g⁻¹ and our study shows that estimated limit of quantifications of ∼120 μg g⁻¹ Br and ∼15 μg g⁻¹ of Cl can be reached. In addition, we show that this new approach permits the acquisition of quantitative Cl and Br maps in minerals, which provide high-resolution insights into crustal fluid properties.