Difficulties in determination of water quality permanganate index

- Jun 23, 2020-

The permanganate index is a comprehensive indicator of the degree of pollution of the reaction water body by organic pollutants and reducing inorganic substances. It is suitable for the determination of relatively clean water bodies such as surface water and drinking water.


It is a relative condition index, and different condition factors will affect its measurement results. In order to find a method for accurately measuring the permanganate index, attention should be paid to the experimental water, heating time, the concentration of potassium permanganate standard solution, the acidity of the reaction system and the control of the titration conditions:

1. Experimental water: The lower the blank value, the lower the content of reducing substances in the water, and the more accurate the experimental results.


2. Heating time: start to count when the sample is placed in the water bath and boil again, and control the heating time at (30 ± 2) min. The potassium permanganate method measures the amount of substances in the water body oxidized by potassium permanganate within 30 minutes, not the total organic matter content, so the heating time will affect the measurement of the permanganate index. If the heating time is too short, the oxidation reaction is insufficient, and the measurement result of the permanganate index is low; if the heating time is too long, the oxidation rate is too high, and the measurement result is too high.


3. Concentration of potassium permanganate standard solution: When the concentration of potassium permanganate standard solution is 0.0100mol / L, the relative error is the smallest and the closest to the true value.


4. Acidity of the reaction system: The acidity of the sample should be strictly controlled, and the concentration of (1 + 3) sulfuric acid reagent should be accurately prepared.


5. Reaction temperature: When the titration temperature is 75 ~ 85 ℃, the concentration of potassium permanganate standard solution basically keeps stable as the temperature rises. The reaction system is in a relatively stable state, neither because the temperature is too low to slow down the reaction rate, nor because the temperature is too high to decompose oxalic acid.


6. Titration time: controlled at 2-3min, the duration of the titration process can not be too long, otherwise the temperature of the reaction system will be affected due to the titration time is too long, affecting the reaction process.


7. End point of titration: when the titration has just appeared pink and does not fade for 30 seconds, it can be regarded as the end point of the titration. Because the pink color is very light, it is not easy to observe. Of the paper in order to observe the color change of the experiment. In addition, when judging the end point of the titration, try to ensure that the end colors of all samples are consistent to make the measurement results comparable.

Introduction of Anjie Technology Automatic Permanganate Index Analyzer: This instrument is suitable for the automatic analysis and detection of permanganate index in surface water, groundwater, drinking water and environmental water, according to the national standard "GB 11892-89 Water quality permanganate" The method of "Salt Index Determination" realizes unattended automatic permanganate index monitoring, thereby achieving more work and more accurate water quality analysis data.