Total Dissolved Nitrogen

For Total Kjeldahl Nitrogen see A071

This method is used for the determination of total dissolved nitrogen in water and wastewater. The range of this method is 0.1 to 10 mg/L, However, this method is also applicable to other ranges.


Organic and inorganic nitrogen-containing compounds are digested at 95°C with alkaline persulfate solution catalyzed by ultraviolet (UV) irradiation. During digestion, liberated nitrogen species are oxidized to nitrate. Nitrate is then reduced quantitatively to nitrite by cadmium metal in the form of an open tubular cadmium reactor (OTCR). The nitrite thus formed is determined as an azo dye at 520 nm following its diazotization with sulfanilamide and subsequent coupling with N-1-naphthylethylenediamine.


Pre-filter turbid samples prior to analysis. EDTA is added during analysis to eliminate interference from iron, copper or other metals. Samples containing large concentrations of oil and grease must be extracted with an organic solvent.


System Method # Range(s)
Flow System A077

0.1 - 10 g/L as N

Astoria 2 A077 0.1 - 10 g/L as N