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How to eliminate the interference of COD detection equipment, you also need to know these precautions!

by:BOQU     2022-02-23

COD detection instrument mainly detects the content of cod in water, which can effectively remove interfering components. So do you know how it eliminates interference, and what should you pay attention to when operating it?

How does the COD detection instrument eliminate interference?

1. Removal of residual chlorine: If there is residual chlorine in the sample, an appropriate amount of sodium thiosulfate solution (ρu003d3.5g/L) can be added to remove it. 0.25 mg of residual chlorine can be removed for every 0.5 ml added. Use starch-potassium iodide test paper to check whether the residual chlorine has been removed.

2. Flocculation precipitation: add 1 ml of zinc sulfate solution (100 g/L) and 0.1~0.2 ml of sodium hydroxide solution (ρu003d250 g/L) to 100 ml of sample, adjust the pH to about 10.5, mix Homogenize, place the precipitate, and tilt the cleaning solution for analysis. If necessary, filter through medium-speed filter paper rinsed with water and discard the initial 20 mL of filtrate. Samples can also be centrifuged after flocculation.

3. Pre-distillation: Transfer 50 ml of boric acid solution (ρu003d20 g/L) into the receiving bottle, and ensure that the outlet of the condenser tube is lower than the surface of the boric acid solution. Take 250 mL of sample, transfer it into a flask, add a few drops of bromothymol blue indicator (ρu003d0.5 g/L), and if necessary, use sodium hydroxide solution (c(NaOH)u003d1 mL/L) or hydrochloric acid solution (c (HCl) u003d 1 ml/L), adjust the pH to 6.0 (the indicator is yellow) ~ 7.4 (the indicator is blue), add 0.25 g of light magnesium oxide, and immediately connect the nitrogen ball and the condenser tube. Heat the distillation so that the distillate velocity is around 10 ml/min. When the distillate reaches 200 ml, stop the distillation and add water to make up the volume to 250 ml.

What should I pay attention to when using COD testing equipment?

1. The digester should be turned on and heated in advance and used after reaching the set temperature.

2. All aspects of water sample pretreatment and the colorimetric process should be completed continuously and compactly.

3. When the solution is used for colorimetry, the outer wall of the cuvette must be kept clean, and there should be no solution, stains, or watermarks.

4. Attention during colorimetry: It is forbidden to stick the colorimetric solution on the colorimetric tank of the measuring instrument or sprinkle it on the colorimetric tank.

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