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COD water quality testerThe research on COD water quality tester methods is relatively early in China. In recent years, the research on COD water quality testers has become more active, and the testing methods are constantly being developed and updated, and the methods are mutually infiltrated. Some methods such as HACH Although the colorimetric method has not been widely used, the method has been approved by the U.S. Environmental Protection Agency. At present, the more mature COD water quality detector methods mainly include the following three: reflux titration method, microwave method, and HACH colorimetric method.
Reflux Titration Method of COD Water Quality Detector:
This method is currently a method commonly used in laboratories.
It is also a national standard method. This method is suitable for all types of water samples with COD values u200bu200bgreater than 30 mg/L, and the upper limit of detection for undiluted water samples is 700 mg/L. The specific method is: add a known amount of potassium dichromate solution to the water sample, and use silver sulfate as a catalyst in a strong acid medium. After boiling and reflux, use ferrous ammonium as an indicator and titrate with ferrous ammonium sulfate. The unreduced potassium dichromate in the water sample is converted into the mass concentration of oxygen consumed by the amount of ferrous ammonium sulfate consumed. The disadvantage of this method is that the operation process is relatively cumbersome, and there are many reasons for errors. For example, reflux collection may cause large errors. After calculation, each drop of ferrous ammonium sulfate can bring about a change of COD value of about 8mg/L, which may cause more Large error; not applicable to water with high chlorine and low COD. The advantages of this method are: the method is relatively mature, and the requirements for the instrument are relatively low.
COD water quality detector microwave method:
The microwave method is a COD test developed in recent years.
Method, this method uses the same sulfuric acid-potassium dichromate digestion system as the reflux method. After the water sample is digested by microwave heating, the excess potassium dichromate is titrated with ferrous ammonium sulfate as an indicator. , Calculate the COD value. A major feature of this method is that the heating of the reaction liquid is carried out by electromagnetic wave energy with a frequency of 2450MHz. Under the action of high-frequency microwaves, the reaction liquid molecules will produce frictional motion. In addition, a sealed digestion method is used to make the pressure of the digestion tank. The rapid increase to 203kPa, so the advantage of this method is that the reaction time is short, and the determination of high-chlorine water can be achieved. The shortcomings of this method are also the shortcomings of titration analysis, so I won't repeat them here.
COD water quality detector HACH colorimetric method:
HACH colorimetry is currently adopted by a few advanced laboratories.
A test method used, this method uses the special bottled digestion solution made by American HACH Company as the digestion reagent. When testing, add a water sample and heat it on a COD reactor manufactured by HACH Company for 2 hours. After cooling to room temperature, use a spectrophotometer manufactured by Hach Company for colorimetric analysis, and read the COD value in the water sample directly. Because Cr2O72- is partially converted to Cr3+ under the action of the reducing agent, the absorbance is measured at a wavelength of 620nm, and then the COD value is converted from the absorbance. The advantage of this method is that it overcomes the errors that may be caused by the titration analysis, and the operation is simple and convenient. Although this method has obvious advantages, it also has certain shortcomings: because the digestion solution uses the special bottled digestion solution of HACH company, the cost of each bottle of the bottled digestion solution is higher.
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