摘要：

Low-temperature ashing of organic samples with oxygen plasma has been currently carried out within the glow discharge region of a plasma chamber operated by an external electrode system. However, ion chromatographic analysis of the residual ash showed that samples containing NaCl or NaBr yielded sifnigicant low recoveries of halogenide as well as oxyhalogenide as a byproduct. This was interpreted to be due to energetic electrons and ions on the sample material. Therefore, a new plasma chamber design consisting of a glass bell jar and a modified internal electrode system was tested for milder oxidation. In this version, sample boats could be situated within a cylindrical sample container that was placed on the lower electrode and electrostatically shielded by wire mesh to eliminate electrons and ions. The results showed higher recoveries of halogenides were obtained with the electrostatic shielding than without it. However, some oxyhalogenides were still found as byproducts. Finally, carbon dioxide plasma was used in place of oxygen plasma to oxidize the organic samples. Quantitative recoveries of chloride or bromide could be obtained, eliminating any detectable signals of oxyhalogenides in the ion chromatogram. X-Ray photoelectron spectroscopy also proved the absence of oxyhalogenides. It was apparent that the use of carbon dioxide plasma for the low-temperature ashing was superior to that of oxygen plasma in terms of quantitative recovery of slightly volatile inorganic components. Such gentle oxidation might be due to the sole presence of atomic oxygen in carbon dioxide plasma whereas in oxygen plasma, ordinary molecular oxygen might also participate in the oxidation process.

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