Applications of a two-step atomizer and related techniques for investigating the processes of sample evaporation and atomization in electrothermal atomic absorption spectrometry

Abstract

A review of the results obtained with special experimental apparatus developed for the investigation of high-temperature processes taking place in the course of atomizing analytes are presented and discussed. The 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. Using 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 atomizer consists of a sample vaporizer and a tube furnace that can be heated to, and held at, a pre-set temperature. The temperature of the vaporizer is controlled automatically by analytical signal feedback. The evaporation 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 inert and hydrogen atmospheres are presented. Molecular spectra of the halides 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 containing oxygen impurities is clarified. An unknown spectrum, probably belonging to AlO molecules, was observed. An explanation of the results obtained, based on Langmuir's theory of evaporation, and developed for the experimental conditions of electrothermal atomic absorption spectrometry, is put forward. The thermodynamic criteria to predict the behaviour of an element in the presence of a reagent are suggested. Calculations of the vapour composition of the oxides of Cd, Zn, Pb, In, Tl, Ga, 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.