Selenium compounds sodium hydride

A modification of the method described in Clesceri et al. (1998) was used to quantify the concentrations of selenite (Se(lV)) in the samples. An aliquot of the filtered sample was reacted with sodium borohydride to distill off any Se(lV) as selenium hydride. The concentration of selenium remaining in solution after the reaction was measured. The difference between original concentration (total dissolved) Se and residual Se in solution is taken as the value for Se(IV). Because of the high concentrations of organo-selenium compounds in the samples, attempts to separate Se(VI) and Se(IV) in the sample by this method (see Clesceri et al., 1998) were not successful. 

Although electrothermal atomisation methods can be applied to the determination of arsenic, antimony, and selenium, the alternative approach of hydride generation is often preferred. Compounds of the above three elements may be converted to their volatile hydrides by the use of sodium borohydride as reducing agent. The hydride can then be dissociated into an atomic vapour by the relatively moderate temperatures of an argon-hydrogen flame. 

Certain volatile elements must be analyzed by special analytical procedures as irreproducible losses may occur during sample preparation and atomization. Arsenic, antimony, selenium, and tellurium are determined via the generation of their covalent hydrides by reaction with sodium borohydride. The resulting volatile hydrides are trapped in a liquid nitrogen trap and then passed into an electrically heated silica tube. This tube thermally decomposes these compounds into atoms that can be quantified by AAS. Mercury is determined via the cold-vapor... 

The question arises as to whether the formation of organometallic compounds during electrolysis of aqueous solutions of acrylonitrile is not due to cyanoethylation of hydrides formed initially at the electrode. In Table 5 data on the electrochemical reduction of tin, sulfur, selenium, and tellurium in aqueous solutions of sodium sulfate with and without acrylonitrile are compared [40]. 

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