Low-temperature transformations of sodium sulfate and sodium selenite in the presence of pre-reduced palladium modifier in graphite furnaces for electrothermal atomic absorption spectrometry

• Published in: Spectrochimica acta. Part B: Atomic spectroscopy 2001-08, Vol.56 (8), p.1387-1396
• Main Authors: Volynsky, Anatoly B., Stakheev, Alexandr Yu, Telegina, Natalia S., Senin, Valery G., Kustov, Leonid M., Wennrich, Rainer
• Format: Article
• Language: English
• Subjects: Electron microprobe analysis; Electrothermal atomic absorption spectrometry; Palladium modifier; Sodium selenite; Sodium sulfate; X-Ray photoelectron spectroscopy
• ISSN: 0584-8547; 1873-3565
• DOI: 10.1016/S0584-8547(01)00251-8

The low-temperature interaction (up to 550°C) of a pre-reduced palladium modifier with sodium sulfate and sodium selenite on the pyrolytic graphite platform was studied using X-ray photoelectron spectroscopy (XPS) and electron microprobe analysis. The equipment applied allowed the introduction of samples heated in an argon flow into the analytical chamber of the XPS spectrometer without contact with the air. Electron microprobe analysis showed that palladium and sulfur preferably occupy different areas on the platform surface. On the contrary, selenium from sodium selenite tends to occupy areas of the graphite surface covered with palladium. The most probable reason for this is the chemisorption of selenium (IV) on the palladium surface at the drying stage. No changes in the XPS spectra of metallic Pd and S 6+ were observed when Na 2SO 4 and Pd were heated together on the graphite platform in the range 100–550°C. The reduction of sodium selenite on the graphite surface already starts during drying. Pre-reduced palladium intensifies this process. The rate of the reduction is proportional to the amount of palladium, and in the presence of palladium at an atomic ratio of Pd/Se=7.5, the transformation of Se 4+ into Se 0 completes at 250°C.