Determination of the total nitrogen content is possible in a single chromatographic step. Ammonium, nitrite and nitrate are separated on a Metrosep A Supp 16 - 250/4.0 column applying UV detection, although ammonium, in contrast to nitrate and nitrite, must run through a post-column derivatization (PCR). Ammonium is transformed into a colored compound in two post-column derivatizations, whereas one chemical suppression prior to UV/VIS detection is sufficient for nitrite and nitrate analysis.