| An evaluation of the particle beam/hollow cathode glow discharge atomic emission spectroscopy (PB-HC-AES) system as an element-specific detector for both liquid chromatographic eluents and dry particulates is described. In the case of liquid analysis, a high-efficiency thermoconcentric nebulizer is used to introduce analyte particles into a heated hollow cathode glow discharge (GD) source for subsequent vaporization, atomization, and excitation. Due to the reduced pressure of the GD source analysis of both metals and atmospheric elements is possible, allowing for empirical formula determinations by calculation of emission response ratios for each element. This was demonstrated through analysis of amino acids and organometallic compounds, where detection limits in the single-to-sub-ppm range were obtained. Implementation of chromatographic separations displayed good correlation between ultraviolet absorbance and atomic emission detection modes.; The direct introduction of particulate matter into a GD atomic emission spectrometry source is accomplished by vacuum action through a narrow stainless steel tube. Particles passing through the aerodynamic momentum separator impinge on the heated (∼200--250°C) surface of the GD plasma volume and are flash vaporized. The resultant atoms/molecules are subjected to excitation/ionization collisions within the low-pressure (0.5--5 Torr He) plasma, producing characteristic photon emission. Limits of detection were on the order of tens of ng for sample masses of ∼50 mug of NIST SRM 1648 Urban Particulate Matter. Sampling of electrostatically-precipitated particles from silicon substrates was also investigated by applying piezoceramic vibrations for particulate removal.; Optimization of the PB-HC-AES system in terms of cathode diameter and temperature was also performed. The effects of current and discharge gas (He) pressure on emission responses were evaluated in flow injection mode for a series of fixed-length (25 mm) cylindrical hollow cathodes having inner diameters of 2, 3, 5, and 7 mm, with optimal responses obtained with the 3-mm i. d. cathode. The effects of vaporization temperature and analyte particle size were investigated by monitoring Cu emission intensity for a series of Cu salts as well as by examining collected particles by scanning electron microscopy. Results indicated an optimum vaporization temperature of 200--300°C, with increased analyte emission intensities achieved through introduction of smaller-sized particles. |
