X-Ray fluorescence spectrometry

X-ray fluorescence spectrometry is used for elemental analysis based on the detection of emitted X-ray radiation from excited atoms. X-rays are short wavelength electromagnetic radiation, a conventional x-ray spectrometer generally utilizes the region of about 0.1 --> 11 nm. This technique is a two-step process that begins with the removal of an inner shell electron of an atom. The resulting vacancy is filled by an outer shell electron. The second step is the transition from the outer shell electron orbital to an inner shell electron orbital. This transition is accompanied by emission of an X-ray photon. The energy of the fluorescent photon is characteristic of the element and is equal to the energy difference between the two electron energy levels. Thus the energy of the fluorescent photon provides qualitative information concerning the elements’ identity. The number or intensity of fluorescent photons is characteristic of the amount or concentration of the elements present. The emission process is similar to other fluorescent measurement techniques. The photon energies are designated (anachronistically) as K, L, or M X-rays depending on the energy level being filled. A K shell (lowest energy, closest to the nucleus) vacancy filled by an L level electron (2nd lowest in energy, one level higher than K shell) results in the emission of a Kα X-ray. There are as many possible X-ray lines, or peaks, as there are inner shell electrons, so things can get complicated very quickly. However K lines are the most analytically useful as they are the most intense. K lines are used for elemental analysis of Na -> Ce. Above Ce in atomic number the K lines are so energetic that the current generation of X-ray detectors cannot detect them. The less intense L and sometimes M lines are used to detect elements throughout the rest of the periodic table. X-ray fluorescence instruments are either energy dispersive x-ray fluorescence (EDXRF) or wavelength dispersive (WDXRF) spectrometers. In either case a source of X-rays is required. In a WDXRF instrument an X-ray monochromator is used prior to the X-rays impinging on the sample. An EDXRF instrument does not possess a monochromator. These multichannel instruments measure all of the emitted X-rays simultaneously, thus EDXRF has the Felgett