Because nitrogen in water is the culprit of eutrophication, it is often the focus of scientific research and engineering technology in the water pollution control industry, and its importance is even less than that of organic pollutants. The analysis of nitrogen in water quality is mainly divided into four aspects: total nitrogen, ammonia nitrogen, nitrate nitrogen and Kjeldahl nitrogen. What is Total Nitrogen, Ammonia Nitrogen, Nitrate Nitrogen, Kjeldahl Nitrogen?
Nitrogen element relationship
The nitrogen entering the water body is mainly divided into inorganic nitrogen and organic nitrogen. Inorganic nitrogen includes ammonia nitrogen (ammonia nitrogen for short) and nitrate nitrogen.
Ammonia nitrogen includes free ammonia nitrogen NH3-N and ammonium salt nitrogen NH4+-N;
Nitrate nitrogen includes nitrate nitrogen NO3--N and nitrite nitrogen NO2--N;
Organic nitrogen mainly includes urea, amino acids, proteins, nucleic acids, uric acid, fatty amines, organic bases, amino sugars and other nitrogen-containing organic compounds
Soluble organic nitrogen mainly exists in the form of urea and protein, which can be converted to ammonia nitrogen by actions such as ammoniation;
Kjeldahl nitrogen includes organic nitrogen and ammonia nitrogen, and does not include nitrate nitrogen.
1. Total nitrogen
Total nitrogen, or TN for short, is one of the most important indicators of water quality. It represents the total amount of inorganic and organic nitrogen in various forms in water, including inorganic nitrogen such as NO, NO, and NH and organic nitrogen such as proteins, amino acids, and organic amines, and is calculated in milligrams of nitrogen per liter of water. Total nitrogen content is often used to indicate the degree to which a water body is contaminated with nutrients. When nitrogen and phosphorus in surface water exceed the standard, eutrophication may occur. Therefore, the determination of total nitrogen content is helpful to evaluate the pollution and self-purification status of water bodies.
2. Nitrate nitrogen
Nitrate nitrogen refers to the element nitrogen contained in nitrate. Organic matter in water and soil decomposes to form ammonium salts, which are oxidized to nitrate nitrogen. Nitrate nitrogen is the main element, plus nitrite nitrogen, ammonia nitrogen and organic nitrogen are collectively called total nitrogen or total (state) nitrogen. In some countries, total nitrogen standards have been set for the quality of lake water. For example, Japan stipulates that the nitrate nitrogen or nitrous (salt) nitrogen in the water does not exceed 10mg l
"Nitrate nitrogen" is used in agriculture to supplement the element "nitrogen", so that crop growth is accelerated, and the crop growth period and harvest period are prolonged. Crops lack "nitrogen" fruit development is stunted, deformed fruits are more, correspondingly speaking, potassium nitrate and other fertilizers play a vital role in the growth of crops, belonging to the three major elements necessary for crop growth.
1.Nitrates
Nitrate in nitrate water is the most stable nitrogen compound in various forms of nitrogenous compounds under aerobic conditions, and is usually used to represent the decomposition product of the final stage of inorganic nitrogen-containing organic matter. Organic nitrogen compounds are considered to be completely decomposed when the water sample contains only nitrate and no other organic or inorganic nitrogen compounds are present. If the water contains a large amount of nitrate and other nitrogen-containing compounds, it means that pollutants have entered the water system and the self-purification of the water is still ongoing.
2.Nitrite
Nitrite is an intermediate product of the nitrogen cycle. Nitrous nitrogen is unstable and can be oxidized to nitrate nitrogen or reduced to ammonia nitrogen. Therefore, by measuring the content of nitrate and ammonia in the water, it is possible to determine the degree of contamination and self-purification of the water system by measuring the content of nitrate and ammonia.
3. Kjeldahl nitrogen
Kjeldahl nitrogen is the amount of nitrogen measured by the Kjeldahl method. It includes ammonia nitrogen and organic nitrogen compounds that can be converted to ammonium salts under these conditions. This type of organic nitrogen mainly refers to proteins, peptones, amino acids, nucleic acids, urea and a large number of synthesized organic nitrogen compounds with negative trivalent nitrogen. Nitrogenous compounds such as azide, azin, azo, hydrazone, nitrate, nitrile, nitro, nitroso, oxime and hemicarbahydrazone are not included. Since most of the organic compounds generally present in water are the former, the difference between Kjeldahl nitrogen and ammonia nitrogen is called organic nitrogen.
4. Ammonia nitrogen
Ammonia nitrogen: Ammonia nitrogen is one of the common water quality testing items in water quality testing, it is an important factor in the eutrophication of the water body, one of the important indicators to measure the degree of pollution of the water body, is the main oxygen consuming pollutant in the water body, and is toxic to fish and some aquatic organisms. Ammonia nitrogen refers to ammonia in the form of free ammonia (or nonionic ammonia, NH3) or ionic ammonia (NH4+). Ammonia nitrogen toxicity is closely related to the pH value and water temperature of the pool water, and in general, the higher the pH value and water temperature, the stronger the toxicity.
It is commonly used to monitor ammonia nitrogen in water, colorimetric method with high sensitivity, salicylic acid spectrophotometry, indigophenol blue light method, and electrochemical analysis method. It is more common to use Nessler's reagent colorimetric method and salicylic acid spectrophotometry to quickly detect ammonia nitrogen in water quality. (The national standard includes Knott's reagent method, salicylic acid spectrophotometry, distillation-titration method).
Determination method] 1. Wash the colorimetric tube 1-2 times with the water sample to be measured, and add the water sample to the 15ml scale line.
2. Add a packet of ammonia nitrogen ( ) reagent.
3. Screw the cap of the colorimetric tube, shake well to dissolve, and let the reaction stand for 2 minutes.
4. Add a packet of ammonia nitrogen ( ) reagent, shake well to dissolve, and let the reaction stand for 15 minutes.
5. Unscrew the tube cap, lift the colorimetric tube to a blank space 1cm high from the color card, and visually determine the color from the tube mouth down to the standard color card.
Among the common ammonia nitrogen detection reagents, Nessler's reagent colorimetric method and salicylic acid reagent use visual colorimetric method, which is simple and convenient to operate, and the technical principle is based on the standard method, the detection is accurate and reliable, and it can be easily detected without professionals for aquaculture water quality testing, which can be used in outdoor, scientific research laboratories and other places.
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