Absorbance vs. time curves at high heating rates in electrothermal atomic absorption spectroscopy

The absorbance vs. time curves that can be obtained in electrothermal atomic absorption spectroscopy with special atomizers and high heating rates can show a very steep increase of the signal from the baseline at the beginning of the atomization step, followed by a more or less extended flat region and by an exponential decay. This type of curve can be mathematically described by simple equations if rather drastic assumptions are made, i.e. if the atom supply is a delta function, if the absorbing species are homogeneously distributed in a plane at the center of a container of constant cross-section, and if the atom removal occurs only by diffusion. In this paper, some experimental curves are presented which are in satisfactory agreement with the theoretical model, thus supporting the claim that, with our atomization system and power supply, the existence of the flat region is indeed justified. With a new atomizer, specifically designed, it is possible to measure the diffusion coefficient of atoms in a gas at high temperature. However, for accurate measurements, the model must be refined and better measurements of the temperature of the atomizer must be obtained.