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Spatial characteristics of a furnace atomization plasma excitation spectometry source

University of British Columbia

Furnace atomization plasma excitation spectrometry (FAPES) is a relatively new atomic emission elemental analysis technique. In FAPES, a radio frequency (r.f.) plasma is created inside the cuvette of a graphite furnace atomizer by applying r.f. power to an electrode placed inside, and coaxial with, the atomization chamber of the cuvette. The plasma provides the energy to excite analyte atoms which then emit the light measured as the analytical signal. In the research reported in this thesis, the spatial structure of this plasma was studied using spectroscopic techniques. Spatially resolved OH and N[sup + over sub 2] molecular and Pb(l) excitation temperature measurements showed that there is a significant thermal gradient in the source with higher temperatures adjacent to the center electrode and cuvette wall. Spatially resolved absorption and emission profiles of an ln(l) line were measured to determine the spatial distributions of ground and excited states in the plasma. The emission profiles contained three concentric emission maxima; the most intense was adjacent to the center electrode, another was adjacent to the cuvette wall, and the third was separated from these maxima by two emission minima. These maxima and minima did not appear in the absorption profiles thus must be due to plasma excitation processes. Spatially resolved magnesium ionization measurements showed that the zones adjacent to the graphite cuvette and center electrode have the highest degree of ionization which causes a decrease in the atomic emission signal at higher r.f. powers. As the pressure in the source was decreased, the emission maxima adjacent to the center electrode and adjacent to the cuvette wall moved away from the graphite surfaces creating dark spaces. These observations suggest that the FAPES source operates as an atmospheric pressure r.f. glow discharge. Two concentric negative glows, adjacent to the cuvette wall and center electrode, are seen where there are maxima in both ionic and atomic emission intensities. Moving away from these glows there are then two Faraday dark spaces. The emission maximum between these is the positive column which exhibits relatively weak ionic emission. Furthermore, cathode dark spaces appear adjacent to each electrode as the pressure is decreased from atmospheric.

Thesis/Dissertation

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2009-02-20

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http://hdl.handle.net/2429/4827

Chemistry

University of British Columbia

UBCV

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