When an electron beam of sufficient energy interacts with a sample target it generates X-rays, as well as derivative electrons (e.g. secondary, back-scattered, auger). A wavelength-dispersive spectrometer uses the characteristic X-rays generated by individual elements to enable quantitative analyses (down to trace element levels) to be measured at spot sizes as small as a few micrometers. WDS can also be used to create element X-ray compositional maps over a broader area by means of rastering the beam. Together, these capabilities provide fundamental quantitative compositional information for a wide variety of solid materials. This technique is complementary to energy-dispersive spectroscopy (EDS) in that WDS spectrometers have significantly higher spectral resolution and enhanced quantitative potential. Many SEM and EPMA instruments have EDS systems mounted to the column, and an EPMA typically has an array of several WDS spectrometers for simultaneous measurement of multiple elements. In typical EPMA applications, EDS is used for quick elemental scans to find out what a material contains, and WDS is then used to acquire precise chemical analyses of selected phases.