1. When testing, the total nitrogen is lower than the ammonia nitrogen. What is the reason?
A: First determine whether the total nitrogen is low or the ammonia nitrogen is high. The detection method of ammonia nitrogen is very simple, but there are too many interferences, which can easily cause the ammonia nitrogen value to be high; if the sample is not completely digested when measuring total nitrogen by UV method, the total nitrogen will also be low, for example, there is a chance that it is not completely digested. There is a certain absorbance under ultraviolet light, and the result will be low.
2. How to adjust the acidity of the water sample preserved by acid for re-measurement?
A: If you are measuring COD and total phosphorus, you don’t need to adjust it again, just test it directly; if you are measuring ammonia nitrogen, you need to use sodium hydroxide solution to adjust the water sample to neutral or weak alkalinity.
3. Is the total nitrogen digestion complete? How to judge?
A: You can judge by UV method. When doing UV colorimetry, observe the absorbance of 275. If it exceeds 0.020, it proves that it is not completely digested. At this time, you can dilute the sample or use K20 reagent and then digest it.
4. How to deal with the red residue in the cuvette after the ammonia nitrogen test?
A: You can use a cotton swab to gently wipe it off, then brush it repeatedly with a brush and tap water, and finally rinse it with pure water.
5. How to deal with high chlorine content in water samples?
A: The common method is to dilute the sample, or use other chlorine-resistant reagents.
6. How often should the ammonia nitrogen reaction tube be replaced?
A: According to the frequency of the experiment and the condition of the reaction tube, it is generally about one year, but there are no specific regulations and requirements. Observe the reaction tube more during use. If there are cracks or scratches, you can replace it.
7. What is the reason for the leakage of the COD special dosing device?
A: When draining, the plug needs to be completely pressed to the bottom; the specific gravity of sulfuric acid at the mouth of the tube is higher and the concentration is higher. Due to gravity, sulfuric acid will drip a few drops. You can put a small beaker below;
If it keeps dripping down and the amount is large, it is likely that there is a sealing problem with the dosing device. At this time, it is recommended to replace a new dosing device.
8. Will calcium ions affect the COD test results?
A: Yes, if there are too many calcium ions, calcium sulfate will be generated, which will affect the COD measurement.
9. Why is the blank value too high for ammonia nitrogen and total phosphorus water samples?
A: The blank water has an impact (the purity of the blank water must be guaranteed). Is it cross-infected by other factors during the experiment?
10. Why does the addition of N2N3 produce red precipitation when ammonia nitrogen is determined?
A: The pH of the sample is too low; 2. The water contains residual chlorine, which needs to be removed with sodium thiosulfate; 3. The ammonia nitrogen concentration in the water is particularly high (rare).
11. The ammonia nitrogen reagent is overdue for half a month. Does it affect the measurement results?
A: It depends on the use and storage conditions on site. You can verify the standard solution and use it within the error range.
12. How much error is normal for two people to do ammonia nitrogen on the same water sample?
A: There are no relevant regulations and standards. It is generally believed that an error within 5% is acceptable.
13. Is the COD measurement accurate with the interference of chloride ions?
A: The error will definitely be larger than that without chlorine, but even if the error is large, it is supported by standards and basis.
14. When doing COD, there is no over-range, why is it turbid?
A: Because the chloride ions in the water are too high, the chloride ions react with the catalyst to form silver chloride precipitation. The sample can be diluted before measurement.
15. Does the digestion instrument need to test the temperature hole by hole?
A: No, the instrument will be temperature calibrated before leaving the factory. Do not calibrate it at will, it is easy to be dangerous.
16. Will high nitrate nitrogen and nitrite nitrogen affect the increase of ammonia nitrogen?
A: It depends on the water environment. Nitrate nitrogen generally does not affect it. Nitrite nitrogen depends on the organisms in the water body. It may be reversed. This situation is rare and generally does not affect it.
Post time: Mar-31-2025
