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Water quality residual chlorine detection methods can be divided into the following three types

by:BOQU     2021-06-07


Methods for the detection of residual chlorine in water quality:

The role of residual chlorine is to ensure continued sterilization and to prevent recontamination of water. However, if the amount of residual chlorine exceeds the limit, it may increase the odor and odor of phenols and other organic substances in the water, and it may also generate form and other organic chlorinated substances with a 'three-factor effect. Determining the residual chlorine content and state in the water is extremely important for the disinfection of drinking water and ensuring the safety of water hygiene.

Principle of water quality residual chlorine detection method:

When there is no iodide ion in the water sample, the free available chlorine will react with the DPD reagent immediately to produce red color, and the addition of iodide ion will play a catalytic role so that the compound chlorine will also react with the reagent to develop color. Separately measure its absorbance to obtain free chlorine and total chlorine, and subtract free chlorine from total chlorine to obtain compound chlorine.

The test method for residual chlorine in water quality clarifies:

The commonly used methods for the determination of residual chlorine are iodometry, N, N-diethyl-p-phenylenediamine-ferrous ammonium sulfate method (DPD method), N, N-diethyl-p-phenylenediamine spectrophotometry, And the colorimetric method of di-o-phenylamine. Common instruments and methods used for combined disinfection monitoring of ClO2 and Cl2.

1. DPD method:

In a weakly acidic solution with a pH of 6.2-6.5, free chlorine can directly react with DPD, and the product is a red substance that can react with ferrous ammonium sulfate, and free chlorine is reduced to Cl-, red disappear. This method is relatively simple and accurate, and it is suitable for the determination of drinking water and industrial water with a measurement range of 0.03-5mg/L.

2. N, N-diethyl-p-phenylenediamine spectrophotometry:

In a solution with a pH of 6.2-6.5, free chlorine can directly react with N, N-diethyl-p-phenylenediamine. The product is a red compound that can be colorimetrically determined at 510nm. This method has high sensitivity and is suitable for the determination of drinking water and industrial wastewater with a residual chlorine content of about 0.05-1.5 mg/L.

3. Lodometric method:

Residual chlorine reacts with potassium iodide in an acidic medium to generate elemental iodine, which can be titrated with Na2S2O3 standard solution. The result of the determination using this method is more accurate. The result of the determination is the total residual chlorine, which is mainly used to determine the total residual chlorine in the daily water. The lower limit of the determination is 1mg/L. 2.2 Bi-o-phenylamine colorimetric method

Under acidic conditions, other oxidants such as Cl2 and chloramine in the solution will oxidize di-o-phenylamine into a yellow compound. When the pH is lower than 1.8, the color of the compound is between the color of the compound and the content of chlorine in the solution. The connection is in accordance with Bill's law. This method is relatively simple and can determine the total residual chlorine and free residual chlorine in the water. It is suitable for the determination of drinking water with residual chlorine in the range of 0.01-10mg/L.

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