TN Analysis


The total nitrogen bound (TNb) is defined as the total pollution of water by nitrogen compounds. It is an analytical parameter for water and is specified in mg/l. The pollution of nitrogen can appear in form of ammonia, ammonium salts, nitrites, nitrates and organic nitrogen compounds.   


Nitrogen is a natural and essential nutrient, but when industry discharges too much nitrogen it can result in algae blooms that deplete oxygen needed by aquatic life (eutrophication).  Nitrogen is an essential nutrient for humans and nature. Today the nutrient contents in water are very high. A further increase would lead to eutrophication (overfertilization). Therefore, it is required to monitor this parameter by online measurement systems and thus enabling the regulation of nutrient concentrations in public water.  Nitrogen-based pollutants can appear in the form of ammonia, ammonium salts, nitrate, nitrite, and organic nitrogen compounds. Monitoring nitrogen in effluent enables industry to discharge at compliant levels, protecting the environment while avoiding surcharges.

Total Bound Nitrogen (TNb) provides a useful, online alternative to laboratory tests. TNb is the sum of all nitrogen compounds and is standardized as DIN EN 12260:2003.  This method detects all forms of nitrogen except molecular nitrogen (N2). It uses high temperature to oxidize all nitrogen compounds into nitrogen monoxide (NO). These reactions take place at temperatures about 700°C. However, higher temperatures more reliably oxidize the nitrogen compounds. The TNb method provides accurate, repeatable, chemical-free results in as little as three minutes per batch. The method is automated, enabling integration into process control systems. Since no re-agents are needed the method is also very low maintenance. 

Standard methods for the determination of nitrogen in water:

  • Kjeldahl nitrogen determination (EN 25663) (TKN = Total Kjeldahl Nitrogen) This method only contains ammonium nitrogen and organic nitrogen compounds.
  • The determination of total nitrogen, according to the German Federal Water Act (WHG/ AbwAG) involves the measurement of the sum of all inorganic nitrogen, such as nitrate, nitrite and ammonia.
  • Koroleff nitrogen determination determines all nitrogen compounds available through a persulphate digestion. Here, a reduction of the resulting nitrate occurs with a copper/cadmium alloy to nitrite, followed by a quantitative determination of nitrite.
  • Nitrogen determination is standardized by the German Institute of Standardization according to DIN EN 12260:2003. This method detects all types of nitrogen except molecular nitrogen (N2) using high temperature oxidation with the support of hydrogen or oxygen. 

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On the market, the determination of the TNb competes with the Kjeldahl nitrogen determination (TKN) and with the persulphate digestion according to Koroleff. In contrast to the TKN, the persulphate digestion and the thermal determination of TNb determines inorganic components such as nitrite and nitrate, too. The methods according to Kjeldahl and Koroleff are time-consuming, labor-intensive and require high amounts of chemicals. Hence, these methods are not suitable for fast and accurate online determination of the nitrogen content.

Total Nitrogen (TN) is the sum of all nitrogen forms or Total Nitrogen = Ammonia Nitrogen (NH3) + Organic Nitrogen (Nitrogen in amino acids and proteins) + Nitrite (NO2) + Nitrate (NO3) or Total Nitrogen = TKN + NO2 + NO3 (This is the formula used to measure nitrogen at wastewater plants).


The thermal determination of TNb is characterized by a high degree of automation, increased accuracy as well as by short measuring cycles. Additionally, the user benefits from the fact that hazardous reagents are not necessary at thermal determination. Commonly two detections of TNb in water samples are used. The detection of the concentration is made with a chemiluminescent- or an electrochemical detector. For chemoluminescence detection ozone is required for the reaction with NO, disadvantaging the approach due to the use of hazardous reagents and the high cost. The electrochemical method is low maintenance, includes lower acquisition costs and the accuracy of its measurement is comparable with the chemiluminescence detection.


Our water analyzers guarantee the complete oxidation of all organic and inorganic compounds with the ultra-high temperature method at 1,200°C. After the oxidation the TNb is detected by an electrochemical sensor. This is an environmentally friendly method that provides very accurate measurement results. The chemiluminescence detector is available as an option with our QuickTONultra. Operators have the option to measure the TNb in combination with TOC and COD

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