Concentration prediction:
Before testing the water sample, first predict the CODmn value of the water sample and select the operation steps corresponding to the range, for example, predict the CODmn concentrationIf the degree value is 0-5mg/L, you need to select the operation step of the 0-5mg/L range; If the CODmn concentration is predicted to be 5-10mg/L, the 5-10mg/L range is chosenProcedure.
Notes:
The digestion of CODmn can be digested by a digester or a Water Bath, and the time should be strictly controlled.
(1) When using a Water Bath to heat, put in blank and water samples after the water boils, and start the timer when the water starts to boil again, reaching a time of 13minImmediately after that, the blank and water samples should be removed and placed in water to cool rapidly.
(2) When using the digestion instrument for heating, when the digestion instrument completes the temperature rise alarm, put the blank and water samples into the digestion instrument to start digestion, and report again when the digestion instrument reportsAfter the alarm, the blank and water samples should be taken out immediately and placed in water to cool rapidly.
1. When the predicted value is in the range of 0 0- -L 5mg/L
If CODmn is present, the water sample appears purplish-red, and the darker the color, the higher the concentration value. Analysis Procedure: CODmnL; Watch out for overrange tips!
2. When the predicted value is in the range of 5 5- - 10L mg/L
If CODmn is present, the water sample appears purplish-red, and the darker the color, the higher the concentration value. Analysis Procedure: CODmnH; Watch out for overrange tips!
3. When the predicted value exceeds 10 mgL /L
The water sample needs to be diluted to the corresponding concentration value in sections 1-2 above, and then operated according to the corresponding range, and the determination result is multiplied by the dilution factor.
4. Test steps on the computer
5. Precautions
◆ If there is CODmn, the water sample shows purple-red, and the darker the color, the higher the concentration value of the water sample.
◆ Pay attention to cross-contamination, use different measuring utensils for different liquids (pay attention to changing the tip when using a pipette).
◆ Use appropriate pipetting tools to take liquids, and large range measuring tools cannot measure small volumes of water samples, such as: 5mL pipettes cannot be used to remove 2mL and below liquidsFor liquids less than or equal to 2mL, it is recommended to pipette twice with a 1mL pipette.
◆ When using a pipette, it is necessary to calibrate the pipette frequently (it is recommended to do so once a week), and pay attention to replacing the tip during use.
