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

Abstract

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 KH₂PO₄, 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 ml min^–1, respectively. The selenium hydride produced is passed through a gas–liquid separator and a dryer tube using an argon carrier flow of 0.45 l min^–1, and Se is determined with a mini-hydrogen diffusion flame by a non-dispersive atomic fluorescence spectrometer equipped with a Se boosted discharge hollow cathode lamp. For total Se determination, samples are acidified (1.5 mol l^–1) and treated with NaBr (4.0% m/v) by heating at 70 °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 (3σ 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.