In the analysis, organically bound nitrogen is converted into ammonium nitrogen. The results from the Kjeldahl method analysis thus comprises organically bound nitrogen and the ammonium nitrogen that was present initially.
The Kjeldahl nitrogen is combined with the sum of nitrogen from nitrite and nitrate into the Total nitrogen content, through the so-called summability method; it is denoted Tot-N_sum in our database. Other methods for analysing the total nitrogen content include the so-called persulphate method (Tot-N_ps) and combustion into nitrogen oxides (TNb).
Known issues with the parameter and/or important method changes
Read more about total nitrogen content analyses at the Department of Aquatic Sciences and Assessment in two assessment on our various methods for analysis of total nitrogen content: Wallman et al. 2009 and Wallman et al. 2011, both in Swedish.
Current methods of measurement
We ceased the analysis of Kjeldahl nitrogen in April 2010. Total nitrogen content is now analysed using the TNb method.
1979-01 – 2010-04
Method: Jönsson, E., Vattenhygien (Water Hygiene, in Swedish), 1966, 22, 10. The ammonium nitrogen is determined according to Swedish Standard SIS 02 81 34.
Instrument: Spectrophotometer UNICAM 8625 with 8mm bandwidth. 10 mm flow-through cuvette. NB: Water samples conserved with HgCl2 in the period 1979-1996. Since 1997-01, water samples are conserved with H2SO4.
1966-01 – 1978-12
Method: Jönsson, E., Vattnehygien (Water Hygiene, in Swedish), 1966, 22, 10. NB: Water samples conserved with HgCl2.
Read about nitrogen on Wikipedia.