Quantitative Electron-probe Microanalysis and WDS Background Measurement

The accuracy of electron-probe microanalysis (EPMA) by wavelength-dispersive spectrometry (WDS) depends critically on spectrometer alignment, specimen positioning, pulse-height (PHA) discrimination, and deadtime correction, but also on the accurate measurement of characteristic x-ray intensities (i.e., “peak”) and continuum (i.e., “background”) which form the k-ratio that is converted by correction algorithms to yield concentration. Using pure elements, oxides, and end-member silicate minerals as primary standards minimizes errors in the selection of WDS background offsets for calibration, whereas the diverse element inventory of samples presents possible interferences for either peak or background due to n th -order diffracted lines from these elements. The use of WDS wavelength scans acquired (using elevated probe current and long count times) on pure elements, primary and secondary standards, and selected samples is valuable in identifying background offsets and assessing the analytical setup. Analysis of secondary standards helps identify systematic errors and is mandatory for quality control.