Selenium appears in the natural selenium cycle in the form of several organic and inorganic compounds. The biologically beneficial and detrimental effects of 'selenium' must be ascribed to particular selenium compounds. The identification and quantification of selenium compounds in biological and environmental samples is required for an understanding of the role of selenium. The highperformance liquid-chromatographic (HPLC) methods for the separation, identification and quantification of selenite, selenate, hydrogen selenide, methaneselenol, bis(organothi0) selenides, trimethylselenonium salts, selenoamino-acids, selenium derivatives of carbohydrates, selenoproteins, selenonucleosides and other miscellaneous selenium compounds are summarized (193 references) and pertinent detection modes discussed. Advantages and disadvantages of the methods are pointed out. The literature is covered since 1974, the year of the first publication in this field.

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A palladium-dispersed carbon paste electrode was used for the electrocatalytic reduction of hydrogen peroxide. After cycling the potential between 0.4 and -0.8V (vs. SCE) in pure dilute alkaline solution M NaOH), the resulting electrode surface exhibited stable and sensitive electrocatalytic response foir hydrogen peroxide. The involved catalytic mechanism was thoroughly investigated. The electrocatalytic effect was attributed to electrogenerated elemental palladium at the electrode surface. The catalytic reduction of hydrogen peroxide proceeds via the hydroxyl radical, OH * . Dissolved oxygen can also be catalytically reduced in a similar way to hydrogen peroxide.The height of the cathodic catalytic current peak, as obtained by linear sweep voltammetry (LSV) was directly proportional to the hydrogen peroxide concentration over a very wide concentration range (0.1-600mgL-'). The detection limit (30) was calculated as 5OpgL-I HzOZ.

Liquid chromatographs, coupled with graphite furnace atomic absorption spectrometers, have been widely used for the identification and quantification of trace element compounds. The quantification of the discontinuous signals from the spectrometer defining a chromatographic band is very much a matter of judgement and therefore prone to error. This paper describes a system which links a high-performance liquid chromatograph via a ‘Brinckman’ flowthrough cup to a Hitachi Zeeman graphite furnace atomic absorption spectrometer equipped with an autosampler. The introduction of aliquots from the column effluent and the analysis sequence is computer-controlled through a home-built interface. The signals from the spectrometer are passed through an analoguedigital converter and processed by selectable algorithms. The software offers a variety of options for processing the chromatographic data, such as data smoothing, Gaussian or spline interpolation, and trapezium or Simpson integration. This system was used to separate and determine selenite and selenate in aqueous solution with absolute detection limits (3 σ) of 23 ng Se for selenite and 16 ng Se for selenate. This system can be adapted to other spectrometers, provided that the required connections to the electronics can be made.