No abstract

The effect of palladium, mixed palladium±magnesium and magnesium modi®ers on the determination of arsenic, antimony and bismuth was tested. It was found that palladium modi®er works correctly only in nitric acid solution. If the sample solution contains hydrochloric acid then palladium becomes a strong interferent and causes signi®cant losses of the analyte. For arsenic and antimony, but not for bismuth, this shortcoming may be eliminated by use of mixed palladium±magnesium or magnesium modi®er. Magnesium modi®er was found to be superior to the mixed modi®er since it is able to eliminate also the negative effects of perchloric acid and of the iron group elements. It is, however, completely ineffective in relation to bismuth when used individually or in a mixture with palladium. Palladium may be used as a modi®er for the determination of antimony and bismuth in hydrochloric acid solution only when it is preliminarily reduced to the metal form. The mechanism of the modi®er activity is discussed.

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The behaviour of selenium and tellurium dissolved in nitric, hydrochloric or perchloric acid and in their mixtures was tested during the atomization process in a graphite tube with a platform. Palladium, magnesium nitrate and their mixture were used as the modi®ers. It was found that palladium is a good modi®er for selenium only in pure nitric or hydrochloric acid solutions. In perchloric acid and in all mixed media, selenium in the presence of palladium is lost almost completely during the evaporation and drying of the sample. Magnesium nitrate used as modi®er is superior to palladium since it thermally stabilizes selenium in all the media investigated up to 1200 ³C. A different situation was found for tellurium. Both modi®ers protect it in all solutions against losses during the ®rst stages of the atomization process; however, magnesium stabilizes it only to 800 ³C whereas palladium is effective up to 1200 ³C. If a mixture of both modi®ers is used in the determination of selenium and tellurium, then its activity is identical with the activity of the component of the mixture that is the more effective when the components are applied individually as modi®er. No effects suggesting a joint action of both components were found. The mechanism of activity of the modi®ers tested is discussed.

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