What are the determination methods of ammonia nitrogen in water? Which method is better? thank you

The determination methods of ammonia nitrogen in China mainly include salicylic acid colorimetry, Nessler's reagent colorimetry and ammonia gas sensitive electrode method. Simply put, there are two kinds: colorimetric method and electrode method. Ammonia gas sensing electrode method is basically used abroad.

Introduction of ammonia gas sensitive electrode method

1. principle

When the pH value is greater than 1 1, ammonium ions are converted into ammonia, and ammonia is transferred through the hydrophobic membrane of the ammonia sensitive electrode, resulting in the change of electromotive force of the ammonia sensitive electrode. The instrument measures the concentration of ammonia nitrogen according to the change of electromotive force.

2. Detection step

Rinse the container for measuring the volume of water sample and reagent and the electrode installation tube with new water sample.

Use a peristaltic pump to inject the sample. The water sample is not in direct contact with the peristaltic pump tube-there is an air buffer zone. The sample volume is controlled by the visual measurement system.

Similar to injection, the auxiliary reagent is also added by peristaltic pump, and the dose volume is controlled by visual system.

Mix water samples and reagents by bubbling.

The reflection time is automatically controlled by the measuring system.

Residual liquid is discharged by peristaltic pump.

In the user-defined measurement cycle, the analyzer will automatically use the built-in calibration standard solution and cleaning solution for calibration and cleaning.

3. How to distinguish the performance of ammonia gas sensor?

3. 1. range: the range specification of ammonia nitrogen by electrode method is: 0-1200; 0-2000; 0-3000; 0- 10000. And the range can be switched freely. The larger the measuring range, the stronger the adaptability of the electrodes used in the instrument.

3.2. Minimum detection limit: The lower the minimum detection limit of the instrument, the better the quality of the representative electrode, generally 0.05 mg/L. ..

4. Comparison between ammonia gas sensitive electrode method and traditional Nessler's reagent colorimetry.

Electrode method

Response time: fast, continuous testing can be realized, the fastest time is only 3 minutes, and the longest time is low-range fine measurement below 1 mg/L 10 minute. The test range is wide, from 0.00- 10000 mg/l NH4-N, and only 1 0 minute is used.

Minimum detection limit: 0.05 mg/L.

Interference: strong anti-interference ability, free from chromaticity and turbidity interference, without additional compensation.

Injection requirements: no special requirements.

The reagent operation cost is low, the electrode method does not need chromogenic reagent, the electrode life is long, the reagent formula is open, and the domestic reagent is adopted, so it is convenient and cheap to buy.

Life span:

The service life of the electrode is long, and the cost of replacing the electrode is low.

colorimetry

Reaction time: slow, can only be tested in batches, and can only be tested after the color reaction is completed. The measurement takes at least 30 minutes.

Test range: small or segmented. When changing the measuring range, a new instrument is needed (the measuring range is determined by the colorimetric cell), and the resolution is low.

Lowest detection limit: 5.0 mg/L.

Interference: It is easy to be interfered by the chromaticity and turbidity of the sample, and the photometric determination is easy to be affected by the change of environmental temperature and humidity.

Sampling requirements: be strict, so as not to pollute the optical components and affect the absorbance test.

Reagent cost: high

Life: the light source is aging, and the cost of replacing the light source is high. Colorimetric cells should be replaced regularly.

I hope my answer can help you!

conclusion

Electrode method is more suitable for on-line testing and analysis. For on-line analysis of nitrogen and phosphorus, electrode method is usually preferred, followed by colorimetric method. At present, the technology of measuring other nutrients (such as nitrate nitrogen, nitrite nitrogen, phosphate, total phosphorus, COD, etc.). ) the method of passing through the electrode is not mature, and a durable electrode has not been developed, so colorimetry is used to replace it temporarily. At present, the technology of measuring ammonia nitrogen by electrode method is very mature, and many well-known professional manufacturers choose electrode method to detect ammonia nitrogen, gradually replacing the old colorimetric method.