Evaluation of an air microwave-induced plasma as an analytical atomic emission source
Urh, John Joseph
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In the past several years, chemists have examined the use of argon, helium and nitrogen plasmas for elemental analysis. This thesis describes the development and analytical behavior of a system which maintains an atmospheric pressure air microwave-induced plasma (AirMIP). Utilizing a 500-watt microwave generator and an internally tuned Beenakker cavity, the system contains air and nitrogen plasmas in a novel torch assembly similar to that of the inductively coupled plasma. With both molecular gas plasmas, the system provides intense elemental emission from pneumatically nebulized solutions. The analytical characteristics of several representative elements were examined with the AirMIP. Parameters examined include calibration curve linearity, emission intensity at several emission lines for each element and detection limits. Also, common analytical interferences (easily ionizable elements, complexing anions, etc.) were characterized. The spectral temperature of the AirMIP and the N2MIP were determined to be approximately 5900 K and 5800 K, respectively. However, the AirMIP exhibits strong correlations between analyte metal-oxygen bond dissociation energies and analytical signal intensity. Data implied that elements with high metal-oxygen bond strengths were poorly atomized.