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Measuring Principle and Interference Effect of Residual Chlorine Meter

by:BOQU     2023-04-06
Residual chlorine analyzer is a commonly used analytical instrument, which can measure residual chlorine, pH value and temperature at the same time, and can be widely used in continuous monitoring of residual chlorine and pH value of various water quality in electric power, waterworks, hospitals and other industries. Measuring principle of the residual chlorine meter When the water sample does not contain iodide ions, the free available chlorine immediately reacts with the DPD reagent to produce red color, and the addition of iodide ions acts as a catalyst to make the combined chlorine react with the reagent to develop color. Measure the absorbance respectively to obtain free chlorine and total chlorine, and subtract free chlorine from total chlorine to obtain combined chlorine. The impact of interference on the residual chlorine meter 1. The presence of alkalinity greater than 250mg/l or acidity of 150mg/l in water, such as CaCO3, will inhibit all color development or the color will fade immediately. Neutralize the sample solution to pH 6-7 with 1N H2SO4 or 1N NaOH. 2. Monochloramine will gradually cause the free chlorine reading to increase. Read within one minute, each 3.0mg/l of monochloramine will increase the free chlorine reading by 0.1mg/l. 3. Oxides of bromine, iodine, ozone and manganese and chromium will increase the free chlorine reading. 4. In order to reduce the influence of Mn4+ and Cr6+, adjust the pH value to 6-7 as above. Take 25ml water sample, add 3 drops of 30g/l KI solution, mix and wait for one minute. Add 3 drops of 5g/l Na2AsO3 and mix (according to the 'Water and Wastewater Standard Test Method', 0.25% thioacetamide solution can be used instead of NaAsO2, and 0.5ml 0.25% thioacetamide is added to each 100ml water sample). If chromium is present, it reacts with DPD in both assays, readout. This reading is then subtracted from the chlorine reading obtained from the initial analysis.
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