SEM/WDS – An Affordable Alternative to EPMA

  • AMMS SEPTEMBER 2019 Publication

    Stephen M. Seddio1 and Sarah N. Valencia2,3

    1. Thermo Fisher Scientific, Fitchburg, Wisconsin, USA.
    2. University of Maryland, Department of Astronomy, College Park, Maryland 20742, USA.
    3. NASA Goddard Space Flight Center, Planetary Geology, Geophysics, and Geochemistry Laboratory, Greenbelt, Maryland 20771, USA.

    The electron microprobe has long been the stalwart tool of mineralogical and petrographic investigation using WDS (wavelength-dispersive spectroscopy), electron imaging, and EDS (energy dispersive spectroscopy). EPMA (electron-probe microanalysis) is a particularly useful analytical technique for the study of planetary and geological materials given its broad analytical range (i.e., B – Pu) and non-destructive nature.

    Scanning electron microscopes (SEM) are much more common, owing to their relatively low cost, but are typically associated only with imaging and perhaps some microanalysis using EDS which may lack some of the analytical rigor typically associated with WDS. However, modern SEM-based X-ray microanalysis systems are able to achieve EPMA-like analysis using standards-based EDS. Additionally, modern X-ray microanalysis systems enable WDS analysis to be performed in an SEM. Here, we compare quantitative WDS analyses of pigeonite, ferroaugite, and pyroxferroite in lunar meteorite NWA (Northwest Africa) 2727 acquired using an electron microprobe and an SEM with results showing that the SEM/WDS system produces data comparable to an EPMA at a much lower cost.