A microwave-induced plasma has been sustained with the use of nitrogen as the nebulizer and plasma supporting gas. A concentric tube torch was constructed so the plasma could be easily ignited and maintained. This new plasma emission source has a flame-like appearance and extends 10 cm beyond the cavity, at an applied power of 250 W. The nitrogen plasma readily accepts aerosol samples and is compatible with sample introduced from a conventional nebulizer system. The radial (side-on) optical viewing configuration was found to have lower background emission than the more commonly employed axial (end-on) configuration. Optimum operating conditions were established from the effects of applied power, flow rate, and signal-to-background noise on the intensity of both atom and ion transitions. A discussion of the background spectral features and the analytical potential of this new source is presented.
R. D. Deutsch and G. M. Hieftje, "Development of a Microwave-Induced Nitrogen Discharge at Atmospheric Pressure (MINDAP)," Appl. Spectrosc. 39, 214-222 (1985)