What is the treatment method for total nitrogen organic matter interference water quality test results?

Total nitrogen, referred to as TN for short, the total nitrogen content in water is one of the important indicators to measure water quality. Total nitrogen is defined as the total amount of all forms of inorganic and organic nitrogen in water. Including inorganic nitrogen such as NO3-, NO2- and NH4+ and organic nitrogen such as protein, amino acid and organic amine, calculated in milligrams of nitrogen per liter of water. It is often used to indicate the degree of water pollution by nutrients. The main methods for the determination of total nitrogen in water quality are: 1. Alkaline potassium persulfate ultraviolet spectrophotometry (HJ 636-2012). 2. Gas-phase molecular absorption spectroscopy: This method is mainly used in laboratories. 3. Ammonia nitrogen, nitrate, and nitrite are also used to measure separately, and then the cumulative value of the results is used as the measurement result of total nitrogen. Typical applications such as Germany WTW. In the field of environmental surface water and water quality monitoring, alkaline potassium persulfate ultraviolet spectrophotometry and optimization methods are currently the main methods. Elimination of interference during the determination of total phosphorus and total nitrogen: 1. Determination of COD: Chloride ion is the main interference component. If the reagent equipped with the instrument has anti-chlorine interference ability, a low range is used to measure COD, which can also reduce the influence of chloride ion on the measurement result. 2. Determination of ammonia nitrogen: when the water sample contains suspended solids, residual chlorine, sulfide and organic matter, it will cause interference, and when it contains such substances, it should be properly treated to eliminate the interference to the determination. 3. If there is residual chlorine in the sample, add an appropriate amount of sodium thiosulfate solution to remove it, and use starch-potassium iodide test paper to check whether the residual chlorine is completely removed. If the water sample is turbid or colored, it can be treated by distillation or flocculation and sedimentation, referring to the national environmental protection standard HJ535-2009. 4. Determination of total phosphorus: As the content of arsenic in the water sample is greater than 2mg/L, there will be interference, which can be removed by sodium thiosulfate. Sulfide content greater than 2mg/L interferes, which can be removed by nitrogen gas under acidic conditions. Hexavalent chromium greater than 50mg/L interferes and is removed with sodium sulfite. Nitrite greater than 1mg/L interferes, and can be removed by oxidative digestion and sulfamic acid. The iron concentration is 20mg/L, which makes the result 5% lower; the copper concentration is 10mg/L and does not interfere; the fluoride is less than 70mg/L and does not interfere. 5. Determination of total nitrogen: there is interference when the chloride ion concentration is higher than 1.5g/L. Other common anions and cations have no interference. Chloride ions can be eliminated by mercuric sulfate. 6. If there are too many suspended solids in the water, it can be detected after filtration with a filter membrane.
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