Precautions when using COD analyzer
1. The maximum amount of chloride ion complexed with 0.4g of mercury sulfate can reach 40mg. If 20.00mL of water sample is taken, the water sample with a maximum chloride ion concentration of 2000mg/L can be complexed. If the concentration of chloride ions is low, you can also add less mercury sulfate to keep mercury sulfate: chloride ion = 10:1 (W/W). If a small amount of mercury chloride precipitates, it will not affect the determination.
2. After the water sample is heated to reflux, the remaining amount of potassium dichromate in the solution should be 1/5-4/5 of the added amount.
3. When using potassium hydrogen phthalate standard solution to check the quality and operation technology of the reagent, since the theoretical CODCr per gram of potassium hydrogen phthalate is 1.176g, dissolve 0.4251g potassium hydrogen phthalate (HOOCC6H4COOK) in Double distilled water, transfer to a 1000mL volumetric flask, and dilute to the mark with double distilled water to make it a 500 mg/L CODcr standard solution. New with time.
4. The determination result of CODCr should retain three significant figures.
5. In each experiment, the standard titration solution of ferrous ammonium sulfate should be calibrated, and special attention should be paid to the change of its concentration when the room temperature is high.