Determination of dissolved inorganic selenium(IV) and selenium(VI) species in natural waters by hydride generation atomic absorption spectrometry

A method is described for the determination of dissolved total inorganic selenium and dissolved selenium(IV) species in natural waters. Reduction of selenium(IV) in the sample with sodium tetrahydroborate(III) results in the evolution of hydrogen selenide. This gas is pre-concentrated in a cryogenic trap, re-volatilised and atomised in an electrically heated quartz furnace aligned in the light beam of an atomic absorption spectrometer. Selenium(VI) species are determined after a pre-reduction with hydrochloric acid. The technique can be employed for the analysis of samples containing between 0.2 and 5 ng of selenium. It is directly applicable over the concentration range 10–200 ng l–1 of selenium but higher concentrations can be determined following suitable dilution. The over-all detection limit of the method is ca. 3 ng l–1 of selenium.