Learn about the preparation method of the relevant standard solution in the detection of residual chlorine

There are relevant standards and methods for the detection of residual chlorine in drinking water and environmental water source water, some of which require the use of buffer solutions, so that they can be offset or reduced during water quality testing, and the pH of the solution itself affects the results. Influence. This ensures 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 solution In the first step, place anhydrous disodium hydrogen phosphate and anhydrous potassium dihydrogen phosphate in an oven at 105 degrees Celsius for 2 hours. After cooling, weigh 22.86g and 46.14g respectively. Then the two reagents weighed out were co-dissolved in pure water. Dilute the dissolved drug to 1000mL with pure water, let it stand for at least 4 days, let the colloidal impurities in it coagulate and precipitate, and then filter. Draw 200.0mL of phosphate buffered saline stock solution, add pure water to dilute to 1000mL, and prepare the final phosphate buffered saline solution. 2. Preparation of potassium dichromate-potassium chromate solution Initially weigh 0.1550 g of dry potassium dichromate and 0.4650 g of potassium chromate. The two weighed agents were dissolved in phosphate buffered saline solution. Use pure water to dilute the dissolved agent to 1000mL. The color produced by this solution is equivalent to the color produced by 1mg/L residual chlorine and o-benzidine. 3. Preparation of o-toluidine standard solution First weigh 1.35 g o-toluidine dihydrochloride. Then, the weighed medicine was dissolved in 500 mL of pure water. Finally, use a mixture of 150mL concentrated hydrochloric acid and 350mL pure water to dilute the dissolved medicine to 1000mL, put it in a brown bottle, and store it at room temperature. 4. Preparation of residual chlorine standard colorimetric solution Take 13 colorimetric tubes, then absorb the potassium dichromate-potassium chromate standard solution according to the quantity shown in the permanent residual chlorine standard colorimetric solution preparation table, and inject 50mL scale stoppers respectively In the colorimetric tube, dilute to the 50mL mark with phosphate buffer solution, then shake gently to make a 0.01-1.0mg/L permanent residual chlorine standard colorimetric tube. To avoid sunlight, it can be stored for about 6 months. If the residual chlorine in the water sample is greater than 1mg/L, then 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 properly dilute it. Obtain the required relatively concentrated residual chlorine standard color column.