Effect of Carbon Dioxide and Hydrogen on Nonmetal Emission Intensities in a Helium Microwave-Induced Plasma

Abstract

The effect of the introduction of carbon dioxide and hydrogen on nonmetal atomic and ionic line intensities in a helium microwave-induced plasma is discussed. The addition of these gases is found to diminish the excitation properties of the 150-W He plasma. While the plasma excitation temperature, ionization temperature, and electron number density are not significantly affected by the introduction of these gases, decreases in the emission intensities of atomic and ionic analyte transitions of S, P, Cl, Br, and I are noted with the higher-energy ionic transitions being more greatly affected. A correlation between the energy of the excited state and the depressing effect of CO₂ is found by examining the signals of atomic and ionic transitions of Cl. The greater signal depression of the higher-energy nonmetal transitions is found to be consistent with charge transfer theory. These findings emphasize the importance of analyte line selection when a He plasma is being employed for the purpose of element-specific detection of nonmetals in supercritical fluid chromatography.