After preseparation of the nitrogen compounds derived from microbial nitrification on a strong basic anion exchanger it is found hydroxylamine together with ammonium in one fraction. The nitrogen of this two compounds can be separated for the emission spectrometric15N analysis by the selective oxidation of the hydroxylamine to nitrite/nitrate using an iodine solution. Thus the hydroxylamine is protected against disproportionation during the following ammonium isolation by means of steam distillation in an alkaline medium. After that the nitrite/nitrate is reduced to ammonium using ferrous hydroxide and can than be librated by steam distillation. The performance of the method under discussion will be demonstrated by analysing solutions with known ammonium and hydroxylamine contents.