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 an d unreduced palladium nitrate modifiers were investigated. It was foun d that stabilization, in both forms, occurred by principally physical processes, as opposed to compound formation. For the unreduced modifie r, it was shown that higher pyrolysis temperatures resulted in a highe r activation energy of atomization and that the selenium vapour-surfac e interaction was increased. The importance of the second high tempera ture step in the stabilization mechanism was stressed, and an addition al conditioning step in the furnace program was proposed for the unred uced 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 x 10(9). For the reduced p alladium modifier, a reduction temperature of 500 degrees C-700 degree s C was shown to be most effective. The reduced palladium modifier sho wed 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 l arge frequency factor (ca. 1 x 10(15)) indicated strong surface intera ctions, thus providing an explanation to the better stabilization prop erties observed for the reduced form of the modifier. (C) 1998 Elsevie r Science B.V.