Is there an extra step in the Winkler titration if the floc in the dissolved oxygen sample will not settle?
Floc in Winkler dissolved oxygen sample will not settle
The floc that forms after adding the first two reagents usually settles to the bottom of the bottle after sitting undisturbed for a few minutes. In samples of high density, however, (for example seawater or very cold samples) the floc may not settle. If the floc does not settle after 5 minutes, proceed to the next step, adding sulfamic acid. Be careful that none of the floc sticks to the stopper when it is removed from the bottle.