Fast heated ballast furnace atomizer for atomic absorption spectrometry Part 1. Theoretical evaluation of atomization efficiency

Abstract

The term ‘ballast’ was introduced in electrothermal atomic absorption spectrometry as an alternative to ‘platform’ in order to describe a compact body (e.g., cylinder) of refractory material loosely located on the bottom of a tube furnace atomizer. In the furnace furnished with ballast, the sample location is not critical, that is, the solution to be analyzed can be injected on the top of the ballast or on the wall next to it. The thermal behavior of the ballast furnace is similar to that of a platform tube atomizer. When the temperature of the tube rapidly rises, the temperature of ballast lags behind. Therefore, if the sample is vaporized from the tube wall, its vapor first undergoes condensation on the colder ballast and then re-evaporation into the absorption volume. Instant gas temperature in the absorption volume depends on heat transfer from both tube wall and ballast. Compared with the flat or concave platform, a compact ballast of similar mass to the platform should have less impact on gas temperatures because of the smaller surface area. Both sample re-evaporation and a higher gas temperature should cause reduction of spectral and chemical interferences. In this work the model of heat and mass transfer is applied to describe the vaporization and atomization of analyte in the tube-, platform- and ballast furnaces. The introduction of the empirical parameters quantifying atomization degree and vaporization rate as a function of temperature permits a comparison between the theoretical efficiencies of the atomizers that differ by size, configuration and heating rate. In particular, theoretical performances are compared using physical parameters of a Quantum Z.ETA longitudinally heated tube (Cortech, Russia) (heating rate 10 K ms⁻¹), furnished with a ballast made of graphite or Ta, and a regular transverse heated THGA atomizer (PerkinElmer) with concave platform (heating rate 2 K ms⁻¹). According to the calculations, a rapidly heated ballast furnace provides more favorable conditions for atomization than a platform tube atomizer. An increase in heating rate allows a reduction in the size of the ballast, which helps eliminate its negative impact on gas temperature in the absorption volume.