Breng, zodra dit blanco monster is genomen, 20 ml natriumhydroxideoplossing (2.2.2.1) in de fles, uitgaande van een totale inhoud van de fles van 750 ml.
Immediately after the blank sample has been removed, add 20 ml of the sodium hydroxide solution (2.2.2.1) in the bottle with a capacity of 750 ml.