Estimation of the possibility of controlling the temperature of an electrothermal atomizer by the signals of the element absorption

Abstract

The current system of the temperature control for the electrothermal atomizer (ETA) used in atomic absorption spectrometers for simultaneous multielement analysis, is unable to provide high characteristics of the analysis when the calibration of the built-in optical pyrometer becomes irrelevant due to the natural wear of graphite cells upon operation. As the control of the ETA efficiency using an external calibrated pyrometer is laborious, it is advisable to use the dependence of temperature on the time of appearance of atomic vapors of elements. We have studied the possibility of controlling the temperature of graphite cells in the electrothermal atomizer of a multielement atomic absorption spectrometer with a continuous spectrum source by the time dependence of absorption signals of chemical elements. The correctness of the calibration was checked by recording the absorption signals of a sample containing chemical elements of different volatility with subsequent evaluation of the time and the corresponding temperature of the appearance of atomic vapors of the elements. The obtained temperatures of the appearance of atomic vapors of Al, Cd, In, Mn, Ni, Pb and V ranged within 640 – 1940°C. When the heating rate is changed by a factor of more than 3, the vapor appearance temperature for the selected elements differs by less than 5%. Using a deliberate change in the calibration of the built-in optical pyrometer, we have simulated a situation in which the relevance of the calibration was lost, e.g., due to the wear of a graphite cell. The experiment revealed a shift of the correlation graph between the actual and measured temperatures of the appearance of vapors of elements in the case of incorrect calibration of the feedback pyrometer in the coordinates «Real temperatures» — «Measured temperatures». The method presented in the study can be used to check the correctness of the calibration of the built-in pyrometer and to determine the necessity of replacing a worn graphite cell.