In addition to the dissolved oxygen sensor measuring oxygen in water, what other methods are there?

Dissolved oxygen (DO) refers to the content of oxygen dissolved in water. It is expressed in milligrams of oxygen per liter of water. Dissolved oxygen exists in the water as a molecule. Dissolved oxygen in water is one of the important indicators for water quality monitoring and one of the important factors for water purification. High dissolved oxygen is conducive to the degradation of various pollutants in the water body, so that the water body can be purified faster; on the contrary, low dissolved oxygen This makes the degradation of pollutants in the water body slower.The size of dissolved oxygen can reflect the pollution of the water body, especially the degree of organic pollution. It is an important indicator for measuring the degree of water pollution and a comprehensive indicator for measuring water quality. Therefore, measuring the dissolved oxygen content of a water body is of great significance for the monitoring of the water environment.To measure dissolved oxygen, the first thing to talk about is the fluorescence method dissolved oxygen sensor[https://www.renkeer.com/product/dissolved-oxygen-sensor/], which uses the fluorescence method measurement principle: modulated blue light shines on the fluorescent substance to excite it and emit red light, because oxygen molecules can take away energy ( Breath-breaking effect), so the time and intensity of exciting red light are inversely proportional to the concentration of oxygen molecules. A red light source synchronized with blue light is used as a reference to measure the phase difference between the excited red light and the reference light and compare it with the internal calibration value to calculate the concentration of oxygen molecules. After some processing, the dissolved oxygen is output. This method has simple and quick steps, fast response time, stable measurement results, no requirement for flow, no interference, reduced cleaning frequency, and low maintenance.In addition, what other methods are available to monitor dissolved oxygen?1. IodometryIodometry is a benchmark method for determining dissolved oxygen in water. It uses a chemical detection method and has high measurement accuracy. It is an earlier method used to detect dissolved oxygen. Add manganese sulfate and alkaline potassium iodide solution to the water to generate manganese hydroxide precipitation. Due to the extremely unstable nature of manganese hydroxide, it quickly reacts with dissolved oxygen in the water to form manganese sulfate. After 15 minutes, concentrated sulfuric acid was added to make the precipitate react with the potassium iodide added in the solution, and iodine was precipitated. The more dissolved oxygen, the more iodine precipitated. Take a certain amount of reaction water sample, use starch as an indicator, and titrate with a standard solution to calculate the dissolved oxygen content in the water sample.The iodine method is suitable for clean water such as source water and surface water. The advantage is that the measurement accuracy is high and the accuracy is good; the disadvantage is that it takes a long time, the procedure is cumbersome, and it cannot meet the requirements of online measurement. The measurement steps are complicated, and the detection time is relatively long, which is not suitable for on-site measurement.2. Amperometric methodThe measurement speed of the amperometric method is faster than that of the iodometric method, the operation is simple, the interference is less, and it can automatically and continuously detect on-site. However, because its oxygen permeable membrane and electrodes are prone to ageing, when the water sample contains algae, sulfide, carbonate, oil and other substances, the oxygen permeable membrane will be blocked or damaged, and it needs to be protected and replaced in time. Because it relies on the electrode itself to undergo oxidation-reduction reaction under the action of oxygen to determine the characteristics of oxygen concentration, oxygen needs to be consumed during the measurement process, so the sample must be constantly stirred during the measurement process, and the electrolyte needs to be replaced regularly, causing it The measurement accuracy and response time of the sensor are limited by diffusion factors.3. Electrode PolarographyElectrode polarography means that a constant voltage is applied between the two electrodes, and electrons flow from the cathode to the anode to generate a diffusion current; at a certain temperature, the diffusion current is proportional to the dissolved oxygen concentration; the quantitative relationship between the current and the dissolved oxygen concentration is established, and then the instrument can The ammeter reading is automatically converted to dissolved oxygen concentration.The electrode polarography method is simple and quick to determine the dissolved oxygen in the water, and the instrument is relatively cheap. It belongs to the national standard method. However, with the consumption of oxygen, fouling will be generated on the membrane and electrodes, and the formation of an oxygen gradient will reduce the reaction rate. If the semi-permeable membrane is damaged, the electrolyte is easily contaminated, which will cause the battery potential to drift, and the drift will be erroneously displayed as the concentration of dissolved oxygen in the water sample, so the electrolyte and semi-permeable membrane need to be replaced regularly.4. Other methodsUse conductive metal thallium or other compounds to react with dissolved oxygen in water to generate conductive thallium ions. By measuring the increase in conductivity in the water sample, the concentration of dissolved oxygen can be obtained. Each increase of 0.035S/cm of conductivity is equivalent to 1mg/L of dissolved oxygen. This method is one of the more sensitive methods for measuring dissolved oxygen and can be used for continuous monitoring.

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