People's lives are inseparable from water resources every day. Tap water is often taken from the rivers and lakes, and then through the complex processing procedures such as sedimentation, filtration, sterilization and so on in the waterworks, and after more than 100 tests and control, it has entered thousands of households, which is what we eat and drink. Therefore, we should cherish the tap water and cherish the water resources.

There are more than 100 testing items in tap water, including organic harmful substances detection, inorganic harmful substances detection, clarity, and harmful ion detection. Among them, residual chlorine detection is one of the most important indicators. Because the water from the rivers and lakes in the waterworks has to be disinfected, the main fungicide is chlorine gas, so chlorine can be left unavoidable in the tap water. Chlorine itself is a very harmful gas. It was used as a poison gas in the war, and it is not harmful to the human body only when the concentration of chlorine in the water is controlled to a very low level. Residual chlorine detection has become an important part of tap water quality control.

The commonly used reagent for residual chlorine detection is TMB, which acts as the guardian of the residual chlorine indicator of our domestic water. As long as the residual chlorine index exceeds the standard, it will warn us that the residual chlorine is too high in bright yellow, so that you know how important TMB is to our domestic water, and it is such a small reagent that bears such a major responsibility. Although the responsibility is significant, the residual chlorine detection reagent prepared by TMB is not very complicated. As long as several reagents and instruments are obtained through weighing and dissolving operations. Here is a brief introduction:

50mL color-comparison tubes

The potassium chloride-hydrochloric acid buffer (pH 2.2): Weighed 3.7g of potassium chloride dried at 100-110°C to a constant weight, dissolved in pure water, plus 0.56mL of hydrochloric acid, obtained by diluting to 1 L with pure water.

3,3',5,5'-tetramethylbenzidine (0.3g/L, i.e. TMB solution): Weigh 0.03g of 3',3,5,5'-tetramethylbenzidine (C16H20N2, with 100mL Hydrochloric acid (0.6 mol/L) was added in portions and stirred to dissolve the reagent (if necessary, the water bath was 40°C (heating and solubilization), and the mixture was mixed. The solution should be colorless and transparent, and stored in a brown bottle.

Potassium dichromate-potassium chromate solution: Weigh 0.1550g of potassium dichromate dried to constant weight at 120°C and 0.4650g of potassium chromate dried at 120°C and dissolved in potassium chloride-hydrochloric acid buffer solution. And diluted to 1L. This solution is equivalent to the color produced by the reaction of 1 mg/L residual chlorine with TMB.

Sample testing: In a 50mL plug colorimetric tube, first add 2.5mL of TMB solution. The tap water sample was added to 50mL, and immediately after mixing, the color was obtained, and the result was free residual chlorine; after standing for 10min, the color result was total residual chlorine.

Edited by Suzhou Yacoo Science Co., Ltd.