Kinetics of selenium atomization in electrothermal atomization atomic absorption spectrometry (ETA-AAS). Part 2: selenium with palladium modifiers

The kinetics of the atomization process of selenium with prereduced and unreduced palladium nitrate modifiers were investigated. It was found that stabilization, in both forms, occurred by principally physical processes, as opposed to compound formation. For the unreduced modifier, it was shown that higher pyrolysis temperatures resulted in a higher activation energy of atomization and that the selenium vapour-surface interaction was increased. The importance of the second high temperature step in the stabilization mechanism was stressed, and an additional conditioning step in the furnace program was proposed for the unreduced palladium modifier. The reaction order for the unreduced modifier was near first order (1.29) with an activation energy of 330 kJ mol⁻¹ and a frequency factor in the order of 1 × 10⁹. For the reduced palladium modifier, a reduction temperature of 500°C–700°C was shown to be most effective. The reduced palladium modifier showed second order kinetics and the activation energy of 500 kJ mol⁻¹, was nearly 50% higher than that of the unreduced form. This and the large frequency factor (ca. 1 × 10¹⁵) indicated strong surface interactions, thus providing an explanation to the better stabilization properties observed for the reduced form of the modifier.