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 electrothermal atomic absorption spectrometry were investigated. Palladium nitrate proved to be superior to palladium chloride for selenium only in pure solutions. In the presence of a chloride matrix, these two chemical modifiers are of similar and rather low effectiveness, whereas ammonium dioxalatopalladate(II), colloidal palladium and a mixture of palladium nitrate and diammonium hydrogen citrate mere found to be more effective. Using these latter modifiers, the chloride matrix does not prevent the formation of metallic palladium at relatively low temperatures. However, maximum modification efficiency was obtained with pre-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 interfere in the determination of 2 ng of selenium. The relatively low effectiveness of colloidal palladium, which was Stabilized with a polymer compound, could be explained by the formation and partial loss of volatile organoselenium compounds. Also, the surface of colloidal palladium is screened off by the polymer causing a rather low accessibility for selenium species.