Titration method:

1. Pre treatment method for triangular flask : Take50mlDeionized water250mlIn a triangular flask, addCOD1ml of manganese reagent I was added to 1.5ml of COD manganese reagent II and boiled in a water bath (100 ℃) for 15 minutes. The triangular flask was taken out and titrated with COD manganese reagent III until it turned slightly red. The solution was then poured out. (Both triangular flasks need to be pre treated).

2. Take 100ml of water sample in a triangular flask, add 5ml of COD manganese reagent I, add 10ml of COD manganese reagent II, and boil in a boiling water bath for 30 minutes.

3.Take off the triangular flask and add 10ml of COD manganese reagent III while hot. Shake well to remove the red color. Titrate with COD manganese reagent II until the solution turns slightly red. Record the amount V1 (ml) of COD manganese reagent II used for titration.