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How does the COD analyzer remove chlorine when measuring COD?

by:BOQU     2021-08-06

Prepare a blank sample containing deionized water and the same chlorine content as the chlorine concentration in your sample. The blank sample will quickly turn into a very dark color after adding the digestive juice, but then you can subtract the influence of chlorine and get a test result that can be applied to your sample.

Where does the error of online COD meter detection mainly come from?

Chlorine is the most influential factor in COD detection. Every COD test bottle used in the potassium dichromate method contains mercury sulfate, a substance that can remove the interference of chlorine whose concentration is listed in the Hach method manual. The vacuum pretreatment device used in the MnIII method can remove chlorine with a concentration of 1000 mg/l.

Can the same COD blank be used for multiple tests?

Multiple experiments using the same experiment bottle can reuse the same blank sample. This blank sample must be kept in a dark place. Continuously measure the absorbance of the blank sample over time to check whether the result is stable. In the absorbance mode, use bottled deionized water to clear the instrument, and then detect the absorbance of the blank sample. Record the test results. When the absorbance changes by more than 0.01 absorbance unit, a new blank sample needs to be prepared.

When the COD value of the water sample is lower than 30, the instrument may output 0. How to avoid it?

Under the premise of confirming that the water sample measurement signal is lower than the distilled water signal, in the calibration cycle interface, the default value for immediate calibration was 1, and it was changed to 2. Then re-calibrate, the COD of the water sample will not be 0.

How to verify the accuracy of COD test results?

Use a COD standard solution whose concentration falls within the concentration range you are using. Treat this standard solution as your sample for testing. If your test results are close to the standard concentration, you can be sure that your instruments and reagents are working properly and that your test is accurate.

The reason why the COD analyzer cannot view the historical data?

First confirm whether the measurement result has been saved.

1. Check whether the currently used curve value (Kv) is set to 0

2. When measuring and taking water samples, whether all the samples including the blank are taken are the same sample

3. Check whether the monochromatic light in the colorimetric cell exists or passes through normally

How to set the COD curve to minimize the error?

The spacing is reasonable, and the gap between the highest point and the lowest point should not be too much. The measured result should be within the range of the curve point as much as possible so that the error will be smaller.

What is the storage temperature of the online cod analyzer?

Working environment conditions are 0-40 degrees Celsius, humidity is not more than 85%, protected from light and moisture.

How to deal with the white precipitate during the COD test?

High chloride ions are prone to this problem. This kind of white precipitate is generally high in chloride ions. It is recommended to increase silver salt or use high-chlorine wastewater detection methods.

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