Preparation method of relevant standard solution for residual chlorine detection

  There are relevant standards and methods for the residual chlorine detection of drinking water and environmental source water. Some of these methods require the use of buffer solutions, so that they can be offset or reduced during water quality testing. The pH of the solution itself affects the results. influences. Ensure the stability of the pH value of the water sample during the measurement. Today we will explain the preparation method of relevant standard solutions for residual chlorine detection.

1. Preparation of phosphate buffer stock solution and buffer

  In the first step, anhydrous disodium hydrogen phosphate and anhydrous potassium dihydrogen phosphate were placed in an oven at 105 degrees Celsius for 2 hours. After cooling, 22.86g and 46.14g were weighed. Then, the two reagents weighed out are co-dissolved in pure water. Dilute the dissolved medicine to 1000 mL with pure water, and let it stand for at least 4 days to coagulate and precipitate the colloidal impurities, and then filter. Draw 200.0mL phosphate buffer stock solution, add pure water to dilute to 1000mL, and prepare the final phosphate buffer solution.

2. Preparation of potassium dichromate-potassium chromate solution

  Initially weigh 0.1550g of dry potassium dichromate and 0.4650g of potassium chromate. The two weighed medicaments are dissolved in phosphate buffer solution. Dilute the dissolved medicine to 1000mL with pure water. The color produced by this solution is equivalent to the color produced by 1mg/L residual chlorine and o-tolidine.

3. Preparation of o-tolidine standard solution

  First, weigh 1.35 g o-tolidine dihydrochloride. Then dissolve the weighed medicine in 500 mL of pure water. Finally, use a mixture of 150 mL of concentrated hydrochloric acid and 350 mL of pure water to dilute the dissolved drug to 1000 mL, put it in a brown bottle, and store it at room temperature.

4. Preparation of residual chlorine standard colorimetric solution

  Take 13 colorimetric tubes, and then draw the potassium dichromate-potassium chromate standard solution according to the quantity shown in the preparation table of the permanent residual chlorine standard colorimetric solution, and inject them into 50mL graduated colorimetric tubes with stoppers, and use phosphate buffer solution Dilute to the 50mL mark, then gently shake to make a 0.01-1.0mg/L permanent residual chlorine standard colorimetric tube. Avoid sunlight, so that it can be stored for about 6 months.

  If the residual chlorine of the water sample is greater than 1mg/L, it is necessary to increase the amount of potassium dichromate-potassium chromate solution by 10 times to prepare a standard color equivalent to 10mg/L residual chlorine, and then appropriately dilute it. Obtain the required concentration of residual chlorine standard color column.

The above is the preparation method of the relevant standard solution when detecting the residual chlorine in the water quality. Of course, if you use the DPD residual chlorine detection method, you do not need to perform these operations.