The permanganate index is a commonly used indicator that reflects the degree of pollution of organic and inorganic oxidizable substances in water bodies. It is defined as: under certain conditions, potassium permanganate is used to oxidize certain organic matter and inorganic reducing substances in water samples, and the equivalent amount of oxygen is calculated from the amount of potassium permanganate consumed.

Depending on the chloride ion content, the permanganate index determination is divided into acidic method and alkaline method. When the chloride ion concentration exceeds 300 mg/L , the alkaline method is used, otherwise the acidic method is used.

When measuring different water samples, we will encounter water samples with various complex components, such as turbid water samples, water samples with suspended matter, and water samples with brown precipitates after digestion and the addition of sodium oxalate (high chloride ion content), which will affect the fully automatic endpoint color determination.

At present, the endpoint determination methods of several commonly used fully automatic instruments on the market are: RGB color sensor, but when the RGB color sensor determines a lighter solution, the value fluctuation is not obvious, and it is impossible to give a signal to determine the endpoint. The liquid reflection and different sample cups have a greater impact on the value fluctuation, the measured value is unstable, and turbid water samples are not easy to identify; another is to determine the endpoint by spectrophotometry. Similarly, spectrophotometry is not easy to identify lighter colors. The reflected light of different sample cups will also have an impact, and the signal response is very slow. In addition, it is impossible to determine turbid water samples with suspended matter, which affects the absorption of wavelengths under specific colors. Through the trial of these sensors, it was found that none of them could solve the problem of light pink color determination at the endpoint of the permanganate index. First, the color recognition effect is not good, second, there are too many interference factors, and third, the communication speed is too slow.

In view of the above shortcomings, the ST108 series high-precision fully automatic permanganate index analyzer developed by our company adopts the internationally leading imported full-color gamut visual simulation sensor for color determination. It is not affected by factors such as turbidity, sample cup, background, light, etc. It uses human eye vision simulation, has powerful image analysis and processing functions, fast response speed, and can process the endpoint color of complex water samples separately (see Appendix 1 ), and meet the color determination of different water samples by switching programs.