Comparative Measurement of Gas Temperature in a Graphite Atomizer by a Two-line Method of Iron and Nickel Spectral Lines in Graphite Furnace Atomic Absorption Spectrometry

Abstract

The gas temperature of atomospheric gas in a graphite atomizer was measured during an atomization stage in graphite furnace atomic absorption spectrometry (GF-AAS), by using a two-line method under the assumption of Boltzmann distribution. Iron and nickel were chosen as the probe elements to compare the gas temperatures obtained with different pairs of spectral lines. The atomic absorptions of two iron atomic lines and those of two nickel atomic lines were simultaneously monitored to obtain their absorbances for the temperature determination. Their gas temperatures were lower than the wall temperature which was monitored by the conventional temperature control for GF-AAS. Furthermore, the temporal variations at the atomizing stage were different between the iron lines and the nickel lines: the maximum peak of the nickel gas temperature appeared to be more delayed and broadly than that of the iron gas temperature. This result could be attributed to the fact that nickel species began to be atomized a little behind iron species, probably because it was more difficult to reduce nickel oxide with graphite carbon than an iron oxide when these oxide species would be formed at the charring stage. A graphite furnace varies the temperature during the atomizing-duration time and also the distribution becomes inhomogeneous at different portions; therefore, the gas temperature would provide overall information along the optical path of incident radiation, when the probe elements diffuse in the furnace. The two-line method enables variations not only in the gas temperature but in the atomizing of probe elements to be directly determined, due to the ability of remote sensing and rapid response.