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First of all, what is residual chlorine? Residual chlorine refers to the available chlorine remaining in the water after the water has been disinfected by chlorination and touched for a certain period of time. The general term for the free chlorine and combined chlorine remaining in the water after chlorine is injected into the water at certain moments of touch. It means that after chlorine is put into the water, in addition to the bacteria, microorganisms, organics, inorganics, etc. in the water, a part of the chlorine is consumed, and a part of the chlorine is left. This part of the chlorine is called residual chlorine.
Residual chlorine can be divided into chemical residual chlorine and free residual chlorine. Total residual chlorine is the sum of chemical residual chlorine and free residual chlorine. Generally, residual chlorine in tap water effluent refers to free residual chlorine. So what should be paid attention to when detecting residual chlorine?
Chlorine is very unstable in an aqueous solution, especially when the concentration is low, the content will rapidly decrease. When exposed to sunlight and other strong lights or agitated, the rate of reduction of chlorine will increase.
Therefore, it cannot be stored after sampling. It is necessary to start the chlorine measurement immediately to avoid light shining and agitating the water sample. All operations in the measurement process should avoid direct sunlight, preferably at the lowest possible temperature and soft light, and all colorimetry methods need to use color and turbidity blanks to compensate for the color and color of the raw water Degree, especially when the turbidity and chromaticity are high, it is necessary to determine the blank value.
When using the o-toluidine visual colorimetric method to determine the residual chlorine, if the water sample is mixed with the standard o-toluidine solution and then the color is compared immediately, the measured result is free residual chlorine, if it is placed in a dark place for 10 minutes Color comparison is performed after the highest chromaticity occurs, and the result is total residual chlorine. The total residual chlorine minus the free residual chlorine is the combined residual chlorine.
When using the o-toluidine visual colorimetric method for determination, if the amount of residual chlorine is large, orange will occur; if the water sample is too alkaline and the amount of residual chlorine is small, light green or light blue will occur. At this time, add 1mL o-toluidine standard solution to produce a normal light yellow.
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