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.

High-speed spectral pyrometer based on a «Kolibri-2» spectrometer

The operation speed of commercially available spectral-ratio pyrometers and brightness pyrometers often appears insufficient for control of fast-changing temperature (e.g., in a graphite cell of an AES electrothermal atomizer, the rate temperature change is 104°C/sec). An advantage of spectral pyrometers is high speed and ability to measure the temperature of objects with unknown emissivity. The goal of this study is to develop a high-speed spectral pyrometer based on a «Kolibri-2» spectrometer with BLPP-2000 photodetector array that provides a wide working wavelength range 400 – 1050 nm, and minimum basic exposure time of 0.4 msec. The temperature was calculated by plotting the emission spectrum of the object in Wien coordinates (with allowance for calibration of the spectral pyrometer using radiation source of the known temperature) and measuring slope of the obtained graph. The relative error of temperature measurements on a spectral pyrometer estimated by comparing measurement results and data obtained with a calibrated Termokont-TN5S1M (Termokont company) single-channel pyrometer was not more than 1.5% in a temperature range of 1000 — 2400°C and higher, and rapidity up to 2500 measurements/sec. The results of measuring temperature of the graphite cell of the electrothermal atomizer using a spectral pyrometer during sample atomization at a rate of temperature change up to 10 000°C/sec are presented.

High-resolution continuum-source electrothermal atomic absorption spectrometer for simultaneous multi-element determination in the spectral range of 190–780 nm

We have built a prototype atomic absorption spectrometer with an electrothermal atomizer and continuum light source for simultaneous multi-element determination.