Water quality residual chlorine monitoring method

Determination of residual chlorine in water (determination of total chlorine free chlorine) 1 o-toluidine colorimetric method 1.
1 Scope of application 1.
1.
1 This method is suitable for the determination of total residual chlorine and free residual chlorine of drinking water and its water sources.
1.
1.
2 Interference determination when the water contains suspended substances, which can be removed by centrifugation.
The permissible content of the interfering substances is as follows: high-speed rail, 0.
2mg/L; tetravalent manganese, 0.
01 mg/L; Nitrite: 0 .
2 mg/L.
1.
1.
3 The low detection concentration of this method is 0.
01mg/L residual chlorine.
1.
2 Principle In an acidic solution with a pH of less than 1.
8, the residual chlorine reacts with o-benzidine to generate a yellow quinone compound, which is colorimetric by visual quantification: the residual chlorine standard solution prepared by potassium dichromate-potassium chromate solution can also be visually colorimetric.
1.
3 Preparation of residual chlorine colorimetric solution 1.
3.
1 Phosphate buffer storage solution: Anhydrous disodium hydrogen phosphate (Na2HPO4) and anhydrous potassium dihydrogen phosphate (KH2PO4) are placed in a 105°C oven for 2h, cooled, and weighed 22.
86g and 46.
14g, respectively.
The two reagents were co-dissolved in pure water and diluted to 1000ml.
Leave on for at least 4 days to allow the colloidal impurities to coagulate and precipitate, filter.
1.
3.
2 Phosphate buffer solution (pH 6.
45): Pipette 200.
0ml phosphate buffer storage solution (1.
3.
1), add pure water to dilute to 1000ml.
1.
3.
3 Potassium dichromate-potassium chromate solution: weigh 0.
1550 g of dried potassium dichromate (K2Cr2O 7) and 0.
4650 g of potassium chromate (K2CrO4), dissolve in phosphate buffer solution (1.
3.
2), and fix the volume to 1000ml.
1.
3.
4 Preparation method of 0.
01~1.
0mg/L residual chlorine standard colorimetric tube: according to the quantity listed in Table 1, pipette potassium dichromate-potassium chromate solution (1.
3.
3), respectively, injected into a 50ml graduated colorimetric tube, and diluted with phosphate buffer solution to a 50ml scale.
Avoid sun exposure and can be stored for up to 6 months.
1.
3.
5 If the residual chlorine of the water sample is greater than 1mg/L, the amount of potassium dichromate-potassium chromate solution should be increased by 10 times, and the standard color equivalent to 10mg/L of residual chlorine should be formed, and then diluted appropriately, that is, the required standard color column of concentrated residual chlorine.
Table 1 Preparation of Residual Chlorine Standard Colorimetric Solution Residual Chlorine, mg/L Potassium Dichromate - Potassium Chromate Solution, ml Residual Chlorine, mg/L Potassium Dichromate - Potassium Chromate Solution, ml 0.
01 0.
03 0.
05 0.
10 0.
20 0.
30 0.
40 0.
5 1.
5 2.
5 5.
0 10.
0 15.
0 20.
0 0.
50 0.
60 0.
70 0.
80 0.
90 1.
00 25.
0 30.
0 35.
0 40.
0 45.
0 60.
0