A Study of Metal Speciation Using a Two-Stage Electrothermal Atomizer. Laser Infrared Fluorescence as a Gc Detector.

Abstract

A. A two-stage atomic absorption atomizer has been designed and built. It consisted of a molybdenum tube atomizer maintained at high temperatures (2200(DEGREES)C for example) and a molybdenum tube vaporizer which was gradually heated from room temperature up to high temperatures. A sample was placed within the latter section when it was cool, and while the former was heated. Subsequently, the vaporization section was gradually heated and the evolved gases were entrained by the carrier gas through the atomization section and into the optical lightpath. Atomic absorption versus temperature curves were obtained for Pb, Zn and Cd compounds. The resultant data were similar in many respects to those obtained by conventional thermal analysis but at much lower concentrations (or about 10('-8) g). Low temperature peaks were observed using the two-stage atomizer indicating atomization of salts volatilized at low temperatures. A similar study with a PE(.)403 graphite furnace revealed no low temperature peaks, presumably because atomization of low temperatures was not achieved. Solutions of lead halides gave peaks corresponding to the vaporized lead halide as well as to the oxide. Similar results were also observed with cadmium solutions. These gave an indication of the form of the metal compounds that was being volatilized from each solution. Lead in air particulates appeared to be present as the oxide and other unidentified forms. This preliminary study indicated that the technique shows high potential for speciation of metal salts at low concentrations. B. Following encouraging work on remote sensing of atmospheric pollutants using laser induced IR fluorescence, the phenomenon was studied as an in situ GC detector. Results showed that collision deactivation on the walls of the detector greatly reduced fluorescence intensity. This essentially vitiated the uses of this technique as a sensitive, continuous flow GC detector.