Direct determination of dissolved selenium(IV) and selenium(VI) in sea-water by continuous flow hydride generation atomic fluorescence spectrometry

Highly sensitive and simple methods were developed for the direct determination of trace amounts of selenite and selenate in sea-water, For Se-IV determination, sea-water samples and reagent blank in 1.5 mol l(-1) HCl containing 2.0% m/v KH,PO,, as an interference eliminating reagent, are merged with 1.5% m/v NaBH4 in 0.5% m/v NaOH using flow rates of 22 and 2.0 mi min(-1), respectively, The selenium hydride produced is passed through a gas-liquid separator and a dryer tube using an argon carrier dow of 0.45 l min(-1), and Se is determined with a mini-hydrogen diffusion flame by a nondispersive atomic fluorescence spectrometer equipped with a Se boosted discharge hollow cathode lamp, For total Se determination, samples are acidified (1.5 moi l(-1)) and treated with NaBr (4.0% m/v) by heating at 70 degrees C for 60 min to reduce selenate, The determination of total Se by atomic fluorescence is then carried out as described above. Se-VI is calculated as the difference between total Se and Se-IV. The detection limits (3 sigma of blank) of the methods were reached with 0.96-1.3 ng l(-1) of Se. The calibration graph was rectilinear up to 80 ng l(-1). The recoveries of 20 ng l(-1) Se-IV added into sea-water were 99.3-100 (s+/-8.4) %, and those of Se-VI were 98.9-104 (s+/-4.0) %. The method is suitable for the direct analysis of natural samples and the results obtained for a certified reference material were in good agreement with the reported value.