Role of Discharge Parameters and Limiting Orifice Diameter in Radio-Frequency Glow Discharge-Atomic Absorption Spectrophotometry (rf-GD-AAS)

Abstract

Studies are performed to evaluate the roles of discharge power and pressure as well as limiting orifice diameter on the production of free, gas-phase atoms with a radio-frequency glow discharge-atomic absorption spectrophotometry (rf-GD-AAS) atomizer. Results indicate that nominal pressures of ∼4 Torr Ar are optimal for conductive samples, whereas a pressure of ∼1 Torr is desired for nonconductive sample types. As might be expected, absorbance signals increase with increases in discharge power to a level of ∼30 W, though trade-offs between ablation rates and source stability exist at higher levels. Completely opposite to the bulk atomization characteristics, large limiting orifice diameters yield higher absorbances. Plasma stabilization times are seen to be on the order of 20 s after initiation of the plasma for conductive and nonconductive sample types. Despite limitations imposed by the current optical instrumentation, it is believed that rf powering in GD-AAS is a viable alternative to conventional dc-powered sources, with the advantage of direct analysis of nonconductive sample types.