METHODS FOR HEATING CONTROL OF GRAPHITE TUBE IN ELECTROTHERMAL ATOMIZER OF ATOMIC-ABSORPTION SPECTROMETER

The research is devoted to the assessment of changes in the degree of blackness (emittance) and electrical resistance of graphite tubes in the electrothermal atomizer of an atomic absorption spectrometer as they wear out. A joint change of these parameters effects on the heating of the atomizer, and, consequently, on the absorption signals of the elements of the periodic table. The heating of the atomizer is controlled by feedback on the temperature, measured using a brightness pyrometer, the measurements of which depend on degree of blackness of the graphite cuvette. Evaluation of the change in the emissivity was carried out by measuring the temperature of the cuvette with a spectral pyrometer, the measurements of which are independent of the emissivity of the controlled object. The electrical resistance, which effects on the heating rate of the cuvette, was calculated after measuring the current and voltage between the contacts of the atomizer. According to the results of the research, we can say that the main contribution to the change in the heating parameters of graphite tubes as they wear out is made by the varying emissivity.