DETERMINATION OF THE TEMPERATURE OF THE GRAPHITE PROBE SURFACE IN GRAPHITE PROBE FURNACE ATOMIC-ABSORPTION SPECTROMETRY

An apparatus for determining the temperature of a graphite probe in gr aphite probe furnace atomic absorption spectrometry has been developed and tested. By measuring the change in the reflection of a laser beam from various pure metals which are deposited on the probe surface at the usual location for sample deposition, it has been found that the h eating of the graphite probe surface occurs in two stages. When the pr obe is inserted into a pulse-heated, commercial graphite furnace after it has been heated to a steady-state temperature, the probe surface i s initially rapidly heated by the radiation from the heated graphite t ube wall, and thereafter the probe maintains that steady-state tempera ture for a short time. For a given graphite probe, the heating rate at the initial stage and the corresponding steady-state temperature at t he final stage are mainly determined by the final tube wall temperatur e; the steady-state temperature of the probe is considerably lower tha n the final tube wall temperature because of thermal conduction by the probe to that part of its body which is lying outside the tube wall. The higher the final tube wall temperature, the higher is the heating rate of the probe at the initial stage, the higher is its steady-state temperature at the final stage, and the less is the difference betwee n the final tube wall temperature and the steady-state temperature of the probe surface. The heating rate of the probe surface at 1600 K is 180 Ks(-1), whereas at 2300 K it is 3600 K s(-1); the differences betw een the probe surface and tube wall temperatures at the former tempera ture is 700 K, whereas at the latter temperature it is 250 K.