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

Abstract This paper focuses on the ability of electron probe microanalyzer (EPMA) or scanning electron microscope (SEM) to yield precise and accurate compositions using wavelength- and energy-dispersive spectrometers (WDS and EDS) for standards-based quantitative X-ray analysis. This approach can be extremely useful to improve analytical capabilities at the micrometer-scale, notably to: (1) reduce the total analysis time; (2) improve the precision and accuracy on minor and trace elements in beam sensitive materials; (3) 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; (4) permit the post-analysis quantification of an unsuspected element; (5) 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); (6) yield a combination of the above, and possibly more. First, we evaluate the reliability of EDS vs. 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 various common rock-forming minerals. In the second step, we compare the analysis of natural and synthetic glass by classical WDS-only EPMA analysis vs. EDS on an SEM, the latter being appreciated for both its standards-based and standardless options. Finally, two real-case applications of combined EDS-WDS analysis are presented: (1) halogens and a few minor to trace elements analysis in apatite (e.g., 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.