State of the art of the methods proposed for selenium speciation analysis by CVG-AFS

Abstract

The inorganic selenium speciation analysis by non-chromatographic methods using atomic fluorescence spectrometry with chemical vapor generation (CVG-AFS) involves the determination of total selenium and Se(IV). Quantification of Se(VI) concentration is obtained by the difference between the total selenium and Se(IV) concentrations. However, the determination of total selenium requires a pre-reduction step of Se(VI) to Se(IV), which is complicated because the kinetics of this reaction is very slow, although thermodynamically favorable. Even chromatographic speciation methods established with detection using CVG-AFS require a pre-reduction step from Se(VI) to Se(IV) because the chemical vapor generation occurs with the Se(IV) species converted to H2Se. This way, several strategies have been proposed for the selenium speciation involving microwave radiation, UV radiation, conventional heating, and different reagents (potassium iodide, sodium bromide, hydrochloric acid, nitric acid, potassium bromate, organic acids), besides co-precipitation and solid-phase extraction procedures. This work reports the advantages and drawbacks of the main techniques employed in selenium speciation studies.