The Se(IV) concentration can be determined by cathodic Stripping Voltammetry (CSV) in an ammonium sulfate electrolyte. The analysis also functions in the presence of Cu. Se(IV) is determined in the first step. In order to register the entire content of Se, Se(VI) species are first reduced to Se(IV). This is handled by the 909 UV Digester at a pH value of between 7 and 9. The method requires practically no reagents and permits selenium speciation.