Several detection methods for COD water quality analyzer

There are several detection methods for COD water quality analyzer, each with its specific principles, advantages and disadvantages, and applicable scope:
Reflux titration method:
Principle: It is mainly suitable for detecting water samples with COD levels greater than 30 milligrams per liter, with a detection upper limit of about 700 milligrams per liter. Through a reflux device, a digestion reaction is carried out in an acidic sulfuric acid medium using potassium dichromate as the oxidant, silver sulfate as the catalyst, and mercury sulfate as the masking agent for chloride ions.
Advantages and disadvantages: The method is mature and requires relatively low instrument accuracy, but the operation is cumbersome and the error is large.
Colorimetric method (spectrophotometric method):
Principle: A spectrophotometer is used for colorimetric analysis. By measuring the absorbance value of hexavalent chromium or trivalent chromium in the water sample and establishing a relationship with the COD value of the water sample, the COD value of the water sample can be determined.
Advantages and disadvantages: Overcome the errors caused by titration analysis, simple operation, but high detection cost.
Microwave method:
Principle: Using microwave digestion method, the water sample is digested by microwave heating, and excess potassium dichromate is titrated with ammonium iron sulfite as an indicator to calculate the COD detection amount.
Advantages and disadvantages: Short reaction time, can achieve the determination of high chlorine water and mixtures, but the operation is cumbersome and requires high professional knowledge in chemistry.
Rapid digestion spectrophotometry:
Principle: A sealed tube is used as the digestion tube. A small amount of water sample and reagent are taken into the sealed tube and placed in a small constant temperature heating dish for constant temperature digestion. The COD value is measured by spectrophotometry.
Advantages and disadvantages: Small space occupation, low energy consumption, low reagent usage, minimal waste liquid, low energy consumption, easy operation, safe and stable, accurate and reliable, suitable for large-scale measurement.
Dichromate reflux method:
Principle: In an acidic sulfuric acid medium, potassium dichromate is used as the oxidant, silver sulfate as the catalyst, and mercury sulfate as the masking agent for chloride ions. The sulfuric acid acidity of the digestion reaction solution is 9mol/L. Heating causes the digestion reaction solution to boil, and ferrous ammonium sulfate solution is used as an indicator to titrate the remaining potassium dichromate. The COD value of the water sample is calculated based on the consumption.
Advantages and disadvantages: The reflux device occupies a large experimental space, consumes a lot of water and electricity, requires a large amount of reagents, is inconvenient to operate, and is difficult to quickly measure in large quantities.
Coulombic titration method:
Principle: Suitable for measuring various water qualities such as drinking water, surface water, industrial wastewater, and domestic wastewater, with good measurement accuracy.
Advantages and disadvantages: The operation process is relatively simple, the measurement speed is fast, but the digestion time is relatively long, and there is significant interference from chloride ions.
UV meter measurement method:
Principle: Suitable for colorless, transparent, and stable water quality measurement, COD value is calculated by measuring the absorbance of the water sample under ultraviolet light.
Advantages and disadvantages: Accurate measurement, low cost, but limited by substances such as ethanol and organic acids that do not have UV absorption properties.
Each of the above methods has its own characteristics, and users can choose the appropriate COD water quality analyzer and its detection method according to their actual needs and conditions.