Food and Drug Administration, 850 Third Ave., Brooklyn, N. Y. 11232 In conventional atomic absorption spectrophotometry a solution of the sample is introduced into the flame as an aerosol by means of a nebulizer. However, commercial nebulizers are only about 5 % efficient in forming fine droplets suitable for

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Selenium was determined by cathodic stripping voltammetry in a 1 mol l-1 HCl acid solution containing added CuII. In this medium, selenium was preconcentrated on the hanging mercury drop electrode and stripped cathodically in differential-pulse mode. After a deposition period of 1 min, 0.2 ng ml-1 of selenium could be detected. The method was applied to the analysis of food supplements. Total selenium was determined after digestion of the sample with HNO3-HClO4 and reduction to the electroactive SeIV by heating with HCl. Inorganic selenium (i.e., selenite and selenate) was similarly determined after extraction with dilute sodium hydroxide solution and clean-up on activated carbon. Representative over-the-counter preparations have been analysed.

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