Sub-stoichiometric isotope dilution analysis for the determination of selenium by liquid scintillation counting

A sensitive and selective sub-stoichiometric isotope dilution method for the determination of trace amounts of selenium is described. The method is based on the extraction of the selenium-dithizone complex with a sub-stoichiometric amount of dithizone into toluene from 7 mol l-1 hydrochloric acid. The activity of the extracted complex was measured by liquid scintillation counting and the counting efficiency was found to be 40%. The calibration graph was linear in the range 0-10 μg of selenium in a final volume of 10 ml. As little as 0.01 μg of selenium can be determined in a total volume of 10 ml. The interferences due to several ions were overcome by using an aluminium hydroxide collection procedure.