When testing the turbidity parameters of water samples, it is a weight technology to ensure the accuracy of turbidity measurement results to be able to accurately prepare the standard solution of formazine. Therefore, as a qualified water quality tester, he should be able to master the preparation method of formazine standard solution, understand the reagents and equipment involved, and the matters needing attention in the operation process.
1. Zero turbidity water
2. Hexatetramethylenetetramine
3. Hydrazine sulfate
4. 50 ml and 100 ml scattered light turbidimeter of volumetric flask.
5. Pipette 5,10,15,20,25ml
6. Analytical balance
7. Ear washing ball
1. Weighing: weigh 10.00g hexamethylenetetramine and 1.000g hydrazine sulfate respectively.
2. Dissolution: dissolve the weighed reagents in a small amount of zero turbidity water.
3. Constant volume: use zero turbidity water to fix the volume of dissolved reagents to 100ml, and then shake to uniform.
4. Prepare the standard stock solution of formazine: transfer 5.00 ml hexamethylenetetramine solution and 5.00 ml hydrazine sulfate solution into a 100 ml volumetric flask, shake well, then stand at 25 ± 3 ℃ for 24 h, and then dilute to the scale. The turbidity of the standard stock solution is 400fnu. The standard stock solution can be kept in the dark at 25 ± 3 ℃ for 4 weeks.
Preparation of standard reference solution of formazine
Take 5.0 ml, 10.0 ml, 12.5 ml, 15.0 ml and 25.0 ml standard stock solution of formazine into 5 50 ml volumetric flasks respectively, dilute them to the scale with zero turbidity water and shake them evenly. Their turbidity are 40, 80, 100, 120 and 200 FNU respectively. The diluted standard solution with turbidity value less than 200fnu can not be stored for a long time, so it should be used along with the preparation. If there are obvious particles in the solution, it indicates that it is invalid.Matters needing attention in the preparation of formazine turbidity standard solution
1. The accurate preparation of formazine standard solution is an important technology to ensure the accuracy of turbidity measurement results. Pay attention to each step of preparing standard solution, shake the original solution evenly, accurately transfer the liquid, pay attention to the scale when pouring the zero turbidity solution, and select large capacity measuring bottle for the standard solution with low turbidity, so as to reduce the preparation error.
2. Select the standard solution for calibration, the content should be the full range value of the measured range, and it should be fully shaken before calibration. For low turbidity measurement and high precision measurement, the difference between sample bottles should be considered, and the same bottle must be used for calibration and detection. Zero turbidity water should be selected for zero calibration, and distilled water can be used when the requirement is not high.
