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 SeIV 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. SeVI is calculated as the difference between total Se and SeIV. 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 SeIV added into sea-water were 99.3–100 (s±8.4) %, and those of SeVI 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.