MECHANISMS OF SELENIUM VAPORIZATION WITH PALLADIUM MODIFIERS USING ELECTROTHERMAL ATOMIZATION AND MASS-SPECTROMETRIC DETECTION

Mass spectrometric sampling of gaseous species that evolve from graphite flats and tubes that are pulse heated in vacuo and from graphite tubes that are pulse heated at 1 atm of pressure was employed in order to elucidate mechanisms controlling selenium electrothermal atomization. Investigations were performed (i) without modifier, (ii) with thermally reduced palladium modifier, and (iii) with nonreduced palladium modifier. Selenium oxides, carbides, hydroxides, dimer, free atom, and palladium were observed as a function of time and temperature during the atomization cycle. The reduced palladium modifier eliminated formation of the molecular selenium species except selenium monoxide. Both SeO and SeO2 were observed when the nonreduced palladium modifier was involved. In both cases, palladium forms a stoichiometric compound with selenium that retains the selenium until higher temperatures are reached.