The relationship between the energy and wavelength is described by the Planck equation: The energy is released in the form of electromagnetic radiation and defines the wavelength of the transition. When electrons return to the stable ground state, energy is emitted and that energy is equal to the difference in the energies between the ground and excited states. The residence time of the unstable excited state is very short, in the order of 10 −8 s. The state of excitation is unstable and decays rapidly. When energy (either thermal, resulting from collision, or radiational, resulting from the absorption of electromagnetic radiation) is applied to an atom and is sufficient to lift an electron from a shell with energy E i to one with E j, the atom is said to be in the excited state. When all the electrons are present in the orbitals, the atoms are in the most stable form (the ground state). Every atom has a certain number of electron orbitals, and each electron orbital has a particular energy level. In the Bohr model, the atom is depicted as a nucleus surrounded by discrete electron orbits, each associated with energy of the order hν. Simulated interference allows spectral lines to be selected for various materials. In order to facilitate spectral line selection in ICP-AES, numerous spectral line atlases are now available which list the best analytical lines and the potential interferences due to coincidences from major and minor constituents. However, spectral lines are emitted by ICP sources that are not emitted by DC arcs and sparks. Other lists are available for spectral lines located in the vacuum UV.Īlthough the relative intensities of spectral lines in the ICP differ from those observed in the DC arc and AC spark, the published tables are invaluable for the selection of analyte lines in ICP sources, and the identification of spectral interferences in the spectrometer bandwidths. The values of the upper and lower energy transitions are listed. The database is accessible over the Internet ( ) and can be searched using either lines or energy levels. The National Institute of Standards and Technology (NIST) Atomic Spectra Database contains ∼72000 spectral lines with intensities observed in a copper arc. The Massachusetts Institute of Technology (MIT) Wavelength Tables list 110000 spectral lines, and the intensities quoted are those observed in DC arcs or alternating current (AC) sparks. In classical emission spectrometry, there are numerous listings of spectral lines. Twyman, in Encyclopedia of Analytical Science (Second Edition), 2005 Line Selection
0 kommentar(er)
