Hanna Instruments HI 904 - Manual (Page 86)

6-4
TITRATION
During the pre-titration, the user cannot change the currently selected method or access the
method parameters.
Note: If the pre-titration lasts longer than 30 minutes the titrator switches to Idle mode.
Errors may have occurred in your titration system (beaker is not properly sealed,
wrong reagent, unconnected or bad electrode, etc.). Check the system and start
pre-titration again.
6.3 Drift Analysis ( Automatic Drift Entry / KF Coulometric only)
While in this mode, the HI 904 conducts an automatic one-minute analysis which determines
the amount of moisture leaking into the cell from the atmosphere. Despite the titration vessel
being tightly sealed, water will still seep into the cell. The amount of water that migrates into
the cell per unit time is known as the background drift rate, or the drift rate.
The drift rate is determined by keeping track of the amount of water that has been titrated to
maintain the ‘dryness’ of the reagent over the course of a minute. The rate at which water
leaks into the cell is then calculated and reported by the HI 904 in units of
µ g/min.
The HI 904 uses the drift rate determined during this state to automatically subtract the
quantity of water which leaks into the cell during a titration from titration results. This is
especially important for titration accuracy when analyzing samples with very low water
content where the amount of water which has leaked into the cell is a considerable fraction of
the total water titrated during the analysis.
When the drift becomes stable the titrator switches to Standby mode.
During the drift analysis, if the titrator cannot maintain cell dryness, the titrator reverts to
pre-titration.
Note: If the drift entry mode is set as Manual, the drift analysis stage is skipped.