Spatially resolved absorbance profiles detailing the selenium vaporisation process in electrothermal atomisers

Abstract

Selenium vaporisation was studied under a variety of conditions using time and spatially resolved absorbance data. The effects of added Ni (as a matrix modifier), O₂ in the gas phase and O₂ chemisorbed on the surface are reported. Conventional pyrolytic graphite coated furnaces, Mo- and Zr-coated furnaces and Ta-lined furnaces were studied. The uniform spatial distribution supports the postulate of Se formation by gas-phase dissociation of SeO or SeO₂. Even with Ni, SeO₂ appears to be released with Se formed in the gas phase. Most Se-graphite interactions are weak with Se uniformly distributed across the furnace. Molybdenum- and Zr-coated furnaces do not show any significant effect on the Se signal. However, Se appears to adsorb to the Ta liner in the absence of a significant O₂ concentrations, thereby producing broadened peaks and non-uniform spatial distributions. Arrhenius plots show little difference in the “apparent activation energy” with added Ni, but they do increase from ca. 40 to 90 kcal with chemisorbed oxygen on the graphite. The largest analytical signal results with chemisorbed oxygen on the graphite and Ni added to the sample. Tantalum-lined furnaces produced maximum peak areas for the systems studied. Mechanisms are discussed.