COMPARISON OF VARIOUS FORMS OF PALLADIUM USED AS CHEMICAL MODIFIERS FOR THE DETERMINATION OF SELENIUM BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

The efficiencies of various chemical modifiers based on palladium for the determination of selenium in the presence of sodium chloride by el ectrothermal atomic absorption spectrometry were investigated. Palladi um nitrate proved to be superior to palladium chloride for selenium on ly in pure solutions. In the presence of a chloride matrix, these two chemical modifiers are of similar and rather low effectiveness, wherea s ammonium dioxalatopalladate(II), colloidal palladium and a mixture o f palladium nitrate and diammonium hydrogen citrate mere found to be m ore effective. Using these latter modifiers, the chloride matrix does not prevent the formation of metallic palladium at relatively low temp eratures. However, maximum modification efficiency was obtained with p re-reduced (at 1000 degrees C) palladium. Using this form of palladium as a chemical modifier, up to 330 mu g of sodium chloride do not inte rfere in the determination of 2 ng of selenium. The relatively low eff ectiveness of colloidal palladium, which was Stabilized with a polymer compound, could be explained by the formation and partial loss of vol atile organoselenium compounds. Also, the surface of colloidal palladi um is screened off by the polymer causing a rather low accessibility f or selenium species.