Quantitative analyses by combined energy and wavelength dispersive spectrometry: The best of both worlds

Abstract

This paper focuses on the ability of an electron probe microanalyzer (EPMA) or a scanning electron microscope (SEM) equipped with wavelength and energy dispersive spectrometers (WDS and EDS) to use both these detectors for their standard-based quantitative X-ray analysis to yield precise and accurate compositions. This approach can be extremely useful to improve the analytical capabilities at the micron-scale, notably to: reduce the total analysis time,improve the precision and accuracy on minor and trace elements in beam sensitive materials,improve the accuracy by choosing WDS analysis for elements suffering from a poor peak-to-background ratio and low count rate on EDS (e.g., trace elements, light elements) or of a strong interference by EDS,permit the post-analysis quantification of an unsuspected element,enable a lifeline to salvage quantitative data after a WDS hardware failure or a change in the environment affecting one or more WDS (i.e., room temperature),or a combination of the above, and possibly more.First, we evaluate the reliability of EDS versus WDS data in geological samples on our EPMA and SEM instruments. A general silicate analysis setup is designed to prove that identical results can be obtained for major and minor elements down to ∼0.5 wt% in a variety of common rock-forming minerals. In the second step, the analysis of natural and synthetic glass by classical WDS-only EPMA analysis versus EDS on an SEM, the latter being appreciated for both its standard-based and standardless options. Finally, two real-case applications of combined EDS-WDS analysis are presented: (1) halogens and few minor to trace elements analysis in apatite, such as S, Ce, Si, Na, Fe, Mg, and Mn at low current and high resolution (≤ 10 nA, 2 to 10 μm beam size) and Ca and P analyzed by EDS, and (2) trace analysis of P-in-olivine (and other elements such as Cr and Al) at high current (≥ 200 nA) and focused beam with Si, Fe, Mg, and Mn by EDS.