TN water analysis refers to the measurement and analysis of Total Nitrogen (TN) content in water samples. Total Nitrogen represents the collective concentration of various forms of nitrogen compounds present in water, including organic nitrogen, ammonia, nitrate, and nitrite.

• 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. 

On the market, the determination of the TN_b 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 TN_b 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_b) 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).

• TNB (Total Nitrogen Bound): TNB refers to the total nitrogen content in a sample, including both organic nitrogen and inorganic nitrogen compounds. It encompasses various forms of nitrogen, such as nitrate (NO3-), nitrite (NO2-), ammonia (NH3/NH4+), organic nitrogen compounds, and other nitrogenous species present in the sample. TNB analysis measures the total concentration of all nitrogen species in the sample without distinguishing between their individual forms.
• TKN (Total Kjeldahl Nitrogen): TKN represents the total organic nitrogen and ammonia nitrogen content in a sample. It specifically measures the sum of organic nitrogen compounds and ammonia nitrogen. TKN analysis involves the digestion of the sample using concentrated sulfuric acid and subsequent distillation to convert organic nitrogen compounds into ammonia. The released ammonia is then captured in a receiving solution and subsequently analyzed using titration or automated colorimetric methods.

The key differences between TNB and TKN are:

• TNB measures the total nitrogen content, including both organic and inorganic nitrogen species, while TKN focuses on organic nitrogen compounds and ammonia nitrogen.
• TNB analysis does not differentiate between the different forms of nitrogen, providing a single measurement for the total nitrogen content.
• TKN analysis involves digestion and distillation to convert organic nitrogen compounds into ammonia for quantification.
• TNB analysis typically requires different analytical techniques, such as colorimetry, spectrometry, or specific ion electrode methods, depending on the nitrogen species of interest.
• TKN analysis often utilizes titration or automated colorimetric methods to measure the ammonia nitrogen concentration.

The thermal determination of TN_b 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 TN_b 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.

Total Nitrogen (TN), it typically involves the use of high-temperature combustion techniques. These methods are often employed to convert all nitrogen compounds, both organic and inorganic, into nitrogen gas (N2) for quantification.

One such technique is known as high-temperature combustion or high-temperature oxidation. In this method, the water sample is introduced into a combustion furnace operating at temperatures typically ranging from 900-1200°C. The organic and inorganic nitrogen compounds present in the sample are oxidized and converted into nitrogen gas.

The evolved nitrogen gas is then purified and passed through a series of traps to remove any potential interfering compounds. Finally, the purified nitrogen gas is quantified using detection techniques such as thermal conductivity detection or chemiluminescence detection.

This high-temperature combustion method provides a measure of the total nitrogen content in the sample, including both organic and inorganic nitrogen species. It does not differentiate between different forms of nitrogen or provide information about specific nitrogen compounds present in the sample.

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 TN_b 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 TN_b in combination with TOC and COD. 

Our LAR ultra-high temperature method for determining Total Nitrogen (TN) in water, typically conducted at around 1,200°C, is effective for several reasons:

• Complete Combustion: The high temperature ensures complete combustion of all nitrogen compounds present in the sample, including both organic and inorganic forms. By subjecting the sample to such extreme temperatures, virtually all nitrogen-containing compounds are oxidized, converting them into nitrogen gas (N2) for quantification.
• Removal of Interfering Compounds: The ultra-high temperature combustion effectively eliminates interfering compounds that might be present in the sample. The intense heat decomposes or converts interfering substances into their elemental components or gaseous forms, ensuring they do not affect the accurate determination of TN.
• Efficient Conversion of Nitrogen Compounds: The high temperature promotes rapid and efficient conversion of various nitrogen compounds into nitrogen gas. It ensures that all forms of nitrogen, such as nitrates, nitrites, ammonia, and organic nitrogen compounds, are transformed into N2, simplifying the analysis by focusing solely on the total nitrogen content.
• Reliable Quantification: After combustion, the evolved nitrogen gas is typically quantified using sensitive and precise detection techniques like thermal conductivity detection or chemiluminescence detection. These methods allow for accurate measurement of the concentration of nitrogen gas, which represents the total nitrogen content in the sample.

Monitoring total organic carbon (TOC), chemical oxygen demand (COD), biological oxygen demand (BOD), and total nitrogen (TN) is essential for maintaining water quality and ensuring compliance with environmental regulations.