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Problems in online monitoring of total phosphorus (what to do if the online monitoring of total phosphorus is inaccurate)

by:BOQU     2022-08-01

Total phosphorus is a general term for orthophosphates, condensed sulfates, pyrophosphates, metaphosphates and phosphates combined with organic groups. It is a key element for algae growth. The main cause of eutrophication in lakes and red tides in bays. In order to effectively detect the content of total phosphorus in water, the online monitoring technology of total phosphorus appeared. However, there are a series of problems in the online monitoring of total phosphorus. This paper mainly introduces the problems and solutions in the online monitoring of total phosphorus.

The main problems in online monitoring of total phosphorus are improper wavelength selection and insufficient color rendering. The standard methods in my country all use 700nm colorimetric determination, but the heteropolyacid used in the online monitoring of total phosphorus has an obvious broad coefficient peak at 690-730nm, and the maximum peak is at 710nm. Moreover, the lakes in our country are different, so different wavelengths are required, and the same wavelength cannot be used, which will cause errors in the results. Therefore, when conducting online monitoring of total phosphorus, the samples should be processed and counted first, and the appropriate wavelength should be selected.

The color development of phosphomolybdenum heteropoly acid method in the online monitoring of total phosphorus will be affected by the configuration and temperature of the solution. Different test solution temperatures will result in completely different color development speeds, resulting in completely different total phosphorus monitoring data. The configuration method of the solution is incorrect, which will also cause unstable color development, resulting in errors in the monitoring results.

In order to solve the problem of improper wavelength selection in online monitoring of total phosphorus, different wavelengths can be selected according to different water samples. 710nm can be used when measuring low content phosphorus, and when measuring high concentration phosphorus, in order to reduce the operation of water sample dilution or avoid introducing dilution errors, 680-750nm wavelength can be used for measurement. In order to solve the problem of insufficient color development, the temperature of the test solution should be controlled and the reasonable configuration of the ammonium molybdate solution should be ensured. Colored water samples are generally better at above 20 degrees Celsius. It is best to develop the standard series and water samples in a water bath of 20 to 30 degrees Celsius for 15 minutes. And in the online monitoring of total phosphorus, it should not be slowly poured into the sulfuric acid solution when preparing the ammonium molybdate solution, otherwise, the color development will be insufficient.

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