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The source of ammonia nitrogen in life and the problems that should be paid attention to when detecting ammonia nitrogen in water

by:BOQU     2023-03-18
Sources of ammonia nitrogen and total phosphorus in domestic sewage: About 50% of the phosphorus comes from urine, 30-40% from faeces, and the remainder from gray water. About 80% of the nitrogen comes from urine, 10% from faeces, and the remainder from gray water. Originally mainly in the form of organic nitrogen (such as urea), it is hydrolyzed by bacteria to ammonia nitrogen during transportation and processing. Problems that should be paid attention to in the analysis and determination of ammonia nitrogen in water: 1. Laboratory environment In the laboratory for ammonia nitrogen analysis, there must be no dust or ammonium salt compounds in the room. Do not carry out analysis items such as nitrate nitrogen at the same time, because ammonia water must be used in the nitrate nitrogen test, and ammonia water is volatile, and the Nessler reagent will absorb ammonia in the air, resulting in high test results. The reagent glassware and other laboratory supplies used should be stored separately to avoid cross-contamination and affect the blank value. 2. The experimental process of preparing ammonia-free water has high requirements on water. Ordinary distilled water often fails to meet the experimental requirements, and secondary treatment is required to obtain ammonia-free water. Based on actual work experience. When distilling to prepare ammonia-free water, the first half of the distillate and the second half of the distillate should be discarded, and only the middle part of the distillate should be stored in a sealed glass bottle. The blank value of the ammonia-free water prepared by this method is low, but the secondary treatment of preparing ammonia-free water is time-consuming and laborious, and uneconomical. Ammonia nitrogen was determined by composite resin exchange column, and fresh deionized water was used instead of ammonia-free water, and the absorbance of the blank met the experimental requirements. 3. Control of reaction conditions 3.1 Reaction temperature Temperature affects the reaction speed of Nessler's reagent and ammonia nitrogen, and significantly affects the color of the solution. When the reaction temperature is 25°C, the color reaction is complete; when the temperature is 5°C-15°C, the absorbance does not change significantly, but the color development is incomplete; when the temperature is 30°C, the solution fades, and the absorbance is obviously low. Therefore, the experimental temperature should be controlled at 20°C to 25°C, so as to ensure the reliability of the analysis results. 3.2 Reaction time Before the reaction time is 10 minutes, the color of the solution is incomplete; 10 minutes to 30 minutes, the color is relatively stable; 30 minutes to 45 minutes, the color tends to deepen; after 45 minutes, the color decreases. Therefore, the color development time should be controlled within 10min to 30min, and the colorimetric analysis should be carried out as soon as possible. 3.3 pH of the reaction system When analyzing the sample, the pH value of the sample has a significant impact on the determination of ammonia nitrogen. If the pH is too low, the color development will not be complete; if the pH is too high, the solution may appear cloudy. When pH=13, the color development will be more complete. And there is no turbidity, so the pH value of the solution is preferably 13. Summary: When using Nessler's reagent to determine ammonia nitrogen spectrophotometrically, attention should be paid to: ① First, qualified reagents must be purchased. ② The correct preparation of reagents determines the sensitivity of the method, especially the preparation of Nessler's reagent. ③ Pay attention to check the experimental water, reagent blank and filter paper. Reducing the blank value can improve the experimental precision. ④ Control the reaction temperature, time, pH value of the system, etc. under the optimal conditions. ⑤ When analyzing a large number of samples, the method of dilution after color development can be directly used, and the result can meet the analysis requirements.
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