The fundamental and practical aspects are described for extracting ions from atmospheric pressure plasma sources into an analytical mass spectrometer. Methodologies and basic concepts of inductively coupled plasma mass spectrometry (ICP-MS) are emphasized in the discussion, including ion source, sampling interface, supersonic expansion, slumming process, ion optics and beam focusing, and vacuum considerations. Some new developments and innovative designs are introduced. The plasma extraction process in ICP-MS was investigated by Langmuir measurements in the region between the skimmer and first ion lens. Electron temperature (T{sub e}) is in the range 2000--11000 K and changes with probe position inside an aerosol …
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The fundamental and practical aspects are described for extracting ions from atmospheric pressure plasma sources into an analytical mass spectrometer. Methodologies and basic concepts of inductively coupled plasma mass spectrometry (ICP-MS) are emphasized in the discussion, including ion source, sampling interface, supersonic expansion, slumming process, ion optics and beam focusing, and vacuum considerations. Some new developments and innovative designs are introduced. The plasma extraction process in ICP-MS was investigated by Langmuir measurements in the region between the skimmer and first ion lens. Electron temperature (T{sub e}) is in the range 2000--11000 K and changes with probe position inside an aerosol gas flow. Electron density (n{sub e}) is in the range 10{sup 8}--10{sup 10} {sup {minus}cm }at the skimmer tip and drops abruptly to 10{sup 6}--10{sup 8} cm{sup {minus}3} near the skimmer tip and drops abruptly to 10{sup 6}--10{sup 8} cm{sup {minus}3} downstream further behind the skimmer. Electron density in the beam leaving the skimmer also depends on water loading and on the presence and mass of matrix elements. Axially resolved distributions of electron number-density and electron temperature were obtained to characterize the ion beam at a variety of plasma operating conditions. The electron density dropped by a factor of 101 along the centerline between the sampler and skimmer cones in the first stage and continued to drop by factors of 10{sup 4}--10{sup 5} downstream of skimmer to the entrance of ion lens. The electron density in the beam expansion behind sampler cone exhibited a 1/z{sup 2} intensity fall-off (z is the axial position). An second beam expansion originated from the skimmer entrance, and the beam flow underwent with another 1/z{sup 2} fall-off behind the skimmer. Skimmer interactions play an important role in plasma extraction in the ICP-MS instrument.
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Niu, Hongsen.Fundamental studies of the plasma extraction and ion beam formation processes in inductively coupled plasma mass spectrometry,
thesis or dissertation,
February 10, 1995;
Iowa.
(https://digital.library.unt.edu/ark:/67531/metadc624492/:
accessed April 24, 2024),
University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu;
crediting UNT Libraries Government Documents Department.