Atomic Line Profiles in Hollow Cathode Lamps and a Glow Discharge Atomizer Determined by Fourier Transform Spectroscopy

Abstract

In an attempt to understand the implications of using glow discharge atomizers in atomic absorption spectrometry (AAS), line profiles and kinetic (Doppler) temperatures were measured in commercial hollow cathode lamps and a laboratory-constructed, jet-assisted dc glow discharge atomizer using a high-resolution Bomem Fourier transform spectrometer. Line profiles were measured in the hollow cathode lamps as current was increased from 1 to 30 mA for three resonance atomic lines (Mg 285.21 nm, Al 308.22 nm, and Pb 283.31 nm) having distinctly different hyperfine structure. Although the Al 308.22-nm line was largely unaffected by self-absorption as the lamp current was increased, the Pb 283.31-nm and Mg 285.21-nm lines exhibited pronounced self-absorption broadening at relatively low lamp currents. Kinetic temperatures in the hollow cathode lamps ranged from 320 ± 20 K at low lamp currents to 840 ± 20 K at high currents. With the use of the Ar(I) 415.86-nm line from the argon discharge gas as a thermometric species, kinetic temperatures of 460 ± 20 K to 620 ± 20 K were measured in the glow discharge atomizer under typical analytical operating conditions. These low atomizer gas temperatures imply that the sensitivity and linear dynamic range of analytical calibration curves will be more strongly affected by the lamp current of the primary radiation source and the spectral properties of the analysis line in glow discharge AAS than in flame or furnace AAS, and that operation at low lamp current is essential for optimal analytical performance. The degrees to which the linear dynamic range and the slope of the analytical calibration curve would be affected by the hyperfine structure of the analysis line, the extent of self-absorption in the hollow cathode lamp, the hollow cathode kinetic temperature, and the glow discharge kinetic temperature are considered separately for each atomic line investigated. The kinetic temperatures in the hollow cathode lamps and the glow discharge atomizer were so close that it was possible to obtain absorption line profiles for the three resonance atomic lines in the glow discharge atomizer with the use of hollow cathode lamps as primary radiation sources, i.e., without the necessity of using a continuum source of radiation.