One of the strongest analytical qualities of energy-dispersive x-ray fluorescence (EDXRF) is the wide range of analyte elements that can be detected and analyzed. Historically, the technique has covered all the elements from sodium (Z=11) and above. A useful measure of specific spectrometer performance is analyte sensitivity. X-ray spectrometric sensitivity is usually expressed in terms of minimum detectable amount of analyte or rate of change of analyte line intensity with change in amount of analyte. Many factors affect analyte sensitivity in EDXRF. These include excitation conditions, specimen conditions, system geometry, atmosphere, detector and readout conditions, and of course the specific analyte line. Typically, EDXRF sensitivity is very good, and low ppm concentrations of analytes are routinely analyzed–until one encounters the light elements.