What are the methods for measuring residual chlorine? What are the pros and cons?

Water quality disinfection can be roughly divided into two methods: physical method and chemical method. The principles of the two methods are basically the same. They are both for the purpose of destroying and preventing microorganisms from replicating and multiplying, so as to cause natural death without causing harm to the human body. Common physical disinfection methods are ultraviolet method and high temperature heating method. The chemical disinfection method is inseparable from the chlorine element. Because of its good effect, high cost performance, simple operation, and other poisoning advantages, the chemical disinfection method is currently the most widely used method in the market. Chlorine gas is highly toxic and easy to remain, which is the biggest feature of the chemical method. If the concentration is insufficient in the water disinfection process, the disinfection will fail, and the water quality will not meet the standard. However, if the concentration exceeds the standard, there will be a major safety hazard to the human body. Therefore, when ensuring water quality, it is necessary to measure the residual chlorine of the water quality to judge whether it meets the standard... 1. Colorimetric method (DPD colorimetric method) residual chlorine (hypochlorous acid and hypochlorite): at pH (PH When the value is between 6.3-6.6, the residual chlorine in the measured water sample will oxidize the DPD indicator into a purple compound. The depth of color development is directly proportional to the residual chlorine content in the sample. At this time, a buffer solution for the measurement of residual chlorine is used, and its function is to maintain the reaction at an appropriate pH value. Total chlorine (the sum of residual chlorine and ammonium chloride): It is determined by adding potassium iodide in the reaction. The ammonium chloride in the sample oxidizes potassium iodide into iodine, and oxidizes the DPD indicator together with residual chlorine (residual chlorine analyzer). The oxide is purple at pH 5.1. A buffer containing potassium iodide was used at this point to maintain the pH of the reaction and provide the potassium iodide required for the reaction. The portable residual chlorine and total chlorine detector is developed and designed based on authoritative certification standards. The detection system adopts an independent optical module (imported) design with excellent optical performance. ⌀16mm optical colorimetric tube is used to simplify the operation steps and no need to transfer liquid. The system adopts a guided operation design with a simple and easy-to-understand interface, enabling operators to use it quickly and accurately. Widely used in scientific research institutes, tap water, medical wastewater, sewage engineering, biomedicine, food dairy, aquaculture, wool spinning printing and dyeing, leather and paper making and other industries for water quality testing and research. Advantages of the instrument 1. Testing items: dozens of testing parameters can be expanded and customized according to needs. 2. Optical system: Adopt independent optical module (imported) design, excellent optical performance, stable and reliable. 3. Operating system: Guided operating system, simple and easy-to-understand interface, guides users to complete operations quickly and accurately. 5. Operating program: a. Built-in system program and user program, and frequently measured items can be added to the user program for easy search. b. It has power-off protection function and one-button factory reset function to prevent data loss. c. The built-in standard working procedures can be used directly, and users can also expand the detection items by themselves. 6. Intelligent detection: standard measurement and continuous measurement can be switched arbitrarily, reducing repeated measurement steps and improving detection efficiency. 7. Professional reagents: special reagents, simplify the operation process, reduce operation errors, use less reagents, and lower the price of consumables. 8. Safe operation: the integrated digestion and colorimetric tube is used to reduce the steps of pipetting the medicine, and the detection is simple, fast and safe. . 9. Color screen display: TFT high-definition color screen display, direct reading of data, simple and time-saving operation. 10. Data transmission: Support USB, network port, Bluetooth and PC or printer for data transmission. 11. Quick printing: support wireless Bluetooth printing, and can print current data and historical measurement data. 12. Data storage: standard working curve and 96 user-defined items, can store 4000 pieces of detection data. 13. Power supply mode: The instrument has a built-in large-capacity rechargeable lithium battery, which has low power and low power consumption, and realizes long standby time. 2. Electrode method (also known as Ampere method) The so-called electrode method is roughly composed of three parts: three-electrode part, electrode membrane cap, and electrolyte. Under the filtration of the membrane cap, the part to be measured enters the electrolyte to undergo a chemical reaction, and the residual chlorine concentration is determined by measuring the current change caused by the chemical reaction in the electrode. It should be noted that because the residual chlorine, chlorine dioxide and ozone in the water body will be continuously consumed, it is necessary to ensure that the water sample continuously flows through the measurement sensor during the test, so maintaining a stable flow rate can ensure the accuracy of the data. The online analog control system instrument has the advantages of simple operation and safe use, multiple temperature compensation methods are optional, and strong anti-interference ability. It can perform single-point online detection of dissolved oxygen, pH/ORP, conductivity, residual chlorine, and total chlorine in water bodies. It is widely used in the detection and control of industrial processes such as drinking water, sewage, scientific research, printing and dyeing, electroplating, and ultrapure water. The industrial residual chlorine online analyzer has a high degree of intelligence and flexibility, microcomputer digital control, and can measure residual chlorine, hypochlorous acid, PH, temperature at the same time. Widely used in continuous online monitoring of residual chlorine and PH value in chemical, metallurgy, water treatment, pharmaceutical, biochemical, electronics, electroplating, printing and dyeing, chemical, food and other industries. Conclusion The above is the main method for the determination of residual chlorine. The data obtained by the colorimetric method has higher accuracy and is very reliable. However, only artificial residual chlorine and total chlorine analysis and testing can be performed on water samples, and continuous measurement and measurement cannot be performed, and the test cost is low. . The electrode method provides continuous feedback on the residual chlorine in the flowing water, and can form linear real-time data. Compared with the colorimetric method, the consumables are less, and the operation steps are relatively simple, but the accuracy is not as high as the colorimetric method. It is mainly used in pools, water Station continuous monitoring and analysis.
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