Total Nitrogen

Total nitrogen (TN_b) is a cumulative parameter. TN_b stands for total bound nitrogen. Both organic nitrogen (urea, peptides, proteins) and inorganic or mineral nitrogen (ammonium/ammonia, nitrate, nitrite) are detected. Gaseous elemental nitrogen N₂ which is contained in the water cannot be determined.

Total nitrogen is the sum of all nitrogen‑containing compounds in a water sample. It is an important parameter in the outflow control of water treatment plants. The nitrogen compounds present in water bodies are mainly degradation or decomposition products of substances containing organic nitrogen (primarily proteins and urea).

As the first inorganic degradation product during bacterial nitrification ammonium NH₄⁺ is obtained, which then reacts via the labile intermediate nitrite NO₂^– to ultimately form nitrate NO₃^–.

One goal of water protection is to protect surface waters against eutrophication from excessive entry of e.g. nitrogen compounds (excessive nutrient loads). To achieve this, the water protection provided by federal and state governments provides for certain discharge conditions which are defined in the water discharge permits, and self-control regulations in the respective states. Important processes for degradation of nitrogen compounds include nitrification and denitrification. Control and optimization of such processes is based on the use and proper documentation of appropriate methods of analysis.

The term Total Kjeldahl Nitrogen (TKN) is defined as the total amount of organically bound nitrogen and ammonia nitrogen. In the presence of detectable amounts of nitrate/nitrite, TKN can be calculated by subtracting the nitrate/nitrite nitrogen from total nitrogen TN_b.

The relationship between these parameters in nitrogen analysis is summarized in the following flow chart:

In an acidic medium, all organic and inorganic nitrogen-containing substances are oxidized to nitrate (in analogy to ISO 7890-1).

The underlying reaction is also analogous to DIN EN ISO 11905-1 and DIN 38405-D9. Nitrate reacts in acidic solution with 2,6-dimethylphenol to form 4-nitro-2,6-dimethylphenol, which can be determined photometrically. In samples with low nitrate and nitrite concentrations, this method (in analogy to ISO 7890-1) yields results similar to the determination of TKN (covering only ammonium and organic nitrogen compounds). In case of detectable amounts of nitrate and nitrite, the TKN value can be determined by subtracting the nitrate/nitrite values from the total nitrogen value TN_b.