APPLICATIONS OF A 2-STEP ATOMIZER AND RELATED TECHNIQUES FOR INVESTIGATING THE PROCESSES OF SAMPLE EVAPORATION AND ATOMIZATION IN ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

A review of the results obtained with special experimental apparatus d eveloped for the investigation of high-temperature processes taking pl ace in the course of atomizing analytes are presented and discussed. T he apparatus provides the means for monitoring the evaporation process of elements from various matrices and the interaction of metals with substrate materials and gases within the atmosphere of the furnace. Us ing molecular vapour absorption spectra the composition of vapours in the analytical zone can be identified. Basic elements of the apparatus include a two-channel spectrometer and a two-step atomizer. The atomi zer consists of a sample vaporizer and a tube furnace that can be heat ed to, and held at, a pre-set temperature. The temperature of the vapo rizer is controlled automatically by analytical signal feedback. The e vaporation characteristics of Ag, Au, Bi, Cd, Co, Cu, Ga, Ge, Pb, Sn, Te, Tl and Zn in the presence of halide and oxygen containing matrices and Ag, Bi, Cd, Co, Ga, In, Mn, Pb, Sb, Sn, Te, Tl and Zn in both ine rt and hydrogen atmospheres are presented. Molecular spectra of the ha lides of Ga, In, Tl, Mg, Ag and oxides of Ga and Al are specified. The atomization mechanism of In, Ga and Al in an inert atmosphere contain ing oxygen impurities is clarified. An unknown spectrum, probably belo nging to AlO molecules, was observed. An explanation of the results ob tained, based on Langmuir's theory of evaporation, and developed for t he experimental conditions of electrothermal atomic absorption spectro metry, is put forward. The thermodynamic criteria to predict the behav iour of an element in the presence of a reagent are suggested. Calcula tions of the vapour composition of the oxides of Cd, Zn, Pb, In, TI, G a, Ge, Ba and Al in the presence of oxygen in the protective gas, were made. Suggestions are made for ways in which the instrument could be further developed.