EPMA WDS Quality Assurance: Materials and Methods

The chief product of an analytical laboratory quality assurance (QA) program, ultimately, is confidenceconfidence that the analysis of any specimen sent to any laboratory participating in the program will be consistent, correct within tolerance, and interchangeable with equivalent analyses of related specimens performed by any other laboratory in the program. In order to maximize confidence, the QA tests and test materials must be chosen such that they evaluate the broadest possible range of instrument functionality. In the context of electron probe microanalysis (EPMA) wavelength dispersive spectroscopy (WDS), this means testing not only the stability of the electron gun and the function of the photon counters, but the functionality of every component of each wavelength spectrometer mounted to the system. This includes the numerous types of diffracting elements that disperse the X-rays, the mechanical components that flip the spectrometer from one diffractor to another, and the drive belts that scan the diffractor through a region of interest on the Rowland circle. Since these spectrometer components can fail independently of the others and many such failures will not be noticeable in all measurements, a complete QA test must include materials that generate X-ray lines that span the range of any diffractor used in WDS and methods to properly analyze it, thus generating the maximum information on the instrument’s function. From this information, instrument performance can be optimized, thereby obtaining maximum analytical confidence.