Shen ChangHong The Nessler's colorimetry is used to measure the ammonia nitrogen in the water by the ammonia nitrogen analyzer. The method has the characteristics of simple operation and high sensitivity. The principle is that the ammonia nitrogen in the form of free ammonia or ammonium ion reacts with sodium reagent to form a yellow brown complex, and the chroma of the complex is directly proportional to the content of ammonia nitrogen. What are the precautions for measuring ammonia nitrogen with the ammonia nitrogen tester?
1、 Precautions for measuring ammonia nitrogen with ammonia nitrogen tester
1. During the experiment, the glassware and colorimetric tube used shall be cleaned with sulfuric acid if necessary.
2. Before the prepared sample is tested on the machine, ensure that the outer wall of the colorimetric tube is wiped clean without water drops or hand marks.
3. For water sample analysis, stand the water sample and take the supernatant for analysis.
2、 How to deal with interference substances when measuring ammonia nitrogen with ammonia nitrogen tester
When there are metal ions, sulfides and organics such as suspended solids, residual chlorine, calcium and magnesium in the water sample, there will be interference. When there are such substances, appropriate treatment shall be done to eliminate the interference to the determination.
1. Remove residual chlorine if the sample contains residual chlorine, add appropriate sodium thiosulfate solution (0.35%), remove 0.25mg of residual chlorine every 0.5ml, and use starch potassium iodide to test whether it is removed completely.
2. The interference of calcium and magnesium ions can be eliminated by complexation masking potassium sodium tartrate.
3. If the water sample is turbid, take 100ml of water sample, add 1.0ml of 10% zinc sulfate solution and 0.1-0.2ml of 25% sodium hydroxide solution, adjust the pH value to about 10.5, mix well, place it to make it precipitate, filter it with medium speed filter paper fully washed without ammonia water, and discard 20.0ml of primary filtrate.
4. If the sample is still turbid and colored after condensation precipitation and complexation masking by distillation, the water sample is treated by distillation.
