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Analysis of COD measuring instrument detection principle

by:BOQU     2021-02-28

Before the COD rapid determination instrument detects the COD content value, the sample needs simple pretreatment.


After adding the chemical oxygen demand reagent for digestion, the detection work is carried out. The digestion process of the water sample directly determines whether the organic matter in the sample can be completely oxidized.


When using a chemical oxygen demand measuring instrument to measure the chemical oxygen demand content in the determination, the chemical oxygen demand digestion instrument needs to be heated to a constant temperature (165°C, 15 minutes), and then placed in the digestion colorimetric integrated tube. Otherwise, the organic matter in the sample cannot be completely oxidized, and the detection result of chemical oxygen demand is lower than the actual value.


The principle of the COD analyzer uses a closed digestion tube for closed digestion. A special oxidant containing a certain amount of potassium dichromate is used in a strong acid solution. Under the action of a catalyst, the water sample is digested at a constant temperature of 165°C for 15 minutes to oxidize the water. The reducing substance.


From the principle of detecting chemical oxygen demand, it can be seen that detecting chemical oxygen demand requires constant heating for 15 minutes in an the environment of 165°C.


However, if the COD digester is first put into the digestion colorimetric integrated tube and then heated, it will take a certain time for the COD digester to heat up from room temperature to 165°C, which will cause the COD to be at 165°C.


The heating time in the C environment is much less than 15 minutes, which leads to the incomplete reaction of the organic matter in the sample, which leads to the detection of the chemical oxygen demand value far lower than the actual value.


Therefore, after the digester is heated to the preset temperature, the digestion colorimetric integrated tube needs to be placed.


In the routine test parameters, in addition to the cod measuring instrument and the multi-functional intelligent digestion instrument, the total phosphorus measuring instrument and the total nitrogen measuring instrument also need to be used in conjunction with the digestion instrument, such as the digestion condition of total phosphorus: 120℃, 30 minutes; the total nitrogen digestion condition is 120°C, 40 minutes; when taking the water sample of the instrument for testing, the digestion process needs to be heated to a constant temperature and then put into the digestion colorimetric integrated tube.

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