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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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