Methods for online analyzers of total nitrogen, nitrate nitrogen, and nitrite nitrogen

So far, the national standard for nitrogen analysis in water quality is mainly divided into five aspects: total nitrogen, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, and Kjeldahl nitrogen. Next, the editor will analyze these five aspects in detail with you. [Total nitrogen] Total nitrogen refers to the nitrogen content in soluble and suspended particles (usually the sum of nitrogen in most organic nitrogen-containing compounds such as nitrate nitrogen, nitrite nitrogen, inorganic ammonium salt, and dissolved ammonia). Soluble total nitrogen refers to the nitrogen content of soluble and filterable solids (particles less than 0.45m) in water. Total nitrogen is one of the important indicators to measure water quality. Determination method of total nitrogen: adopt the method of separately measuring organic nitrogen and inorganic nitrogen compounds (ammonia nitrogen, nitrite nitrogen, nitrate nitrogen) and adding them; after oxidation with potassium persulfate to convert organic nitrogen and inorganic nitrogen into nitrate , measure the nitrate ion in the solution by ion-selective electrical method; it can also be determined by ultraviolet method or after reduction to nitrite, azo colorimetric method, and ion chromatography. The total nitrogen online analyzer uses the ultraviolet colorimetric method. 【Ammonia Nitrogen】Ammonia nitrogen refers to ammonia in the form of free ammonia (or non-ion ammonia, NH3) or ion ammonia (NH4+). The higher the pH, the higher the proportion of free ammonia; conversely, the higher the proportion of ammonium salts. Two colorimetric methods of approximate sensitivity commonly used to determine ammonia are the classic Nessler's reagent method and the phenol-hypochlorite method; titration and electrical methods are also commonly used to determine ammonia; distillation can also be used when the ammonia nitrogen content is high -titration. (National standards include Nessler's reagent method, salicylic acid spectrophotometry, distillation-titration method). The ammonia nitrogen online monitor uses potassium persulfate oxidation ultraviolet-visible spectroscopy, Nessler's reagent, and colorimetric methods such as expelling. [Nitrate Nitrogen] Nitrate in water is a stable nitrogen compound in various forms of nitrogen-containing compounds under aerobic conditions, and is usually used to represent the decomposition product of the final stage of inorganic nitrogen-containing organic matter. When the water sample only contains nitrate and no other organic or inorganic nitrogen compounds are present, the decomposition of organic nitrogen compounds is considered complete. 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 in progress. The determination methods of nitrate nitrogen include ion selective electrometry, phenol disulfonic acid spectrophotometry, cadmium column reduction method, ultraviolet spectrophotometry, Dai's alloy exchange method, ion chromatography, and ultraviolet method. Among them, the electrical method is convenient to measure, has a wide range, and is cheap, and has lower requirements for water samples; the phenolic disulfonic acid spectrophotometric method has a wide measurement range and stable color development; the cadmium column reduction method is suitable for the determination of low-content nitrate in water; Alloy exchange method is suitable for heavily polluted and dark water samples; ion chromatography requires special equipment, but can be combined with other anions. The nitrate nitrogen online analyzer uses an optical method. 【Nitrite Nitrogen】 Nitrite is an intermediate product of the nitrogen cycle. Nitrite nitrogen is unstable and can be oxidized to nitrate nitrogen or reduced to ammonia nitrogen. Therefore, while measuring its content, and knowing the content of nitrate and ammonia in the water, it is possible to judge the degree of pollution of the water system by nitrogen-containing compounds and the self-purification situation. The determination method of nitrite in water usually adopts diazo-coupling reaction to generate red-purple dye. The method has high sensitivity, low detection limit and strong selectivity. The diazonium reagent uses p-aminobenzenesulfonamide and p-aminobenzenesulfonic acid, and the coupling reagents are N-(1-naphthyl)-ethylenediamine and -naphthylamine (toxic), N-(1-naphthyl)-ethane Diamines are used more often. The determination methods of nitrite nitrogen include N-(1-naphthyl)-ethylenediamine spectrophotometry, extraction spectrophotometry, ion chromatography, gas chromatography and so on. (The national standard uses N-(1-naphthyl)-ethylenediamine spectrophotometry, gas chromatography, etc.). Nitrite nitrogen (nitrite nitrogen) online analyzer uses photoelectric colorimetry. 【Kjeldahl nitrogen】 Kjeldahl nitrogen is the nitrogen content measured by the Kjeldahl method. It includes ammonia nitrogen and organic nitrogen compounds that can be converted to ammonium salts under these conditions. This kind of organic nitrogen mainly refers to protein, peptone, amino acid, nucleic acid, urea and a large amount of synthetic organic nitrogen compounds with negative trivalent nitrogen. Azide, diazo, azo, hydrazone, nitrate, nitrile, nitro, nitroso, oxime and semicarbazone nitrogen-containing compounds are not included. Since the organic compounds generally present in water are mostly the former, after measuring Kjeldahl nitrogen and ammonia nitrogen, the difference is called organic nitrogen. The principle of determination is to add sulfuric acid to heat and digest, so that the amine group, free ammonia and ammonium salt in the organic matter are converted into ammonium bisulfate, and the digested liquid is made alkaline to distill ammonia, absorbed in boric acid solution, and then titrated or Ammonia content was determined photometrically. The determination of Kjeldahl nitrogen or organic nitrogen is mainly to understand the pollution of water bodies, especially when evaluating the eutrophication of lakes and reservoirs, it is a meaningful indicator.