Metrohm 796 Titroprocessor - Manual (Page 110)

7.3 MET Monotonic equivalence point titration
796 Titroprocessor, Instructions for use 104 104
7.3 MET Monotonic equivalence point titration
Application:
MET modes are flexible titration modes for titrations which do not provide S-
shapes titration curves or for kinetic inhibited titration reactions. Their typical
features are constant dosing increments at regular or drift-dependent time
intervals and automatic equivalence point recognition.
The equivalence point evaluation is carried out on the basis of the Fortuin
method with an optimized evaluation algorithm.
Important: reagent addition and measurement acceptance can also be
optimally adapted for demanding applications. However, incorrectly se-
lected parameters such as too large volume increments can easily produce
imprecise results.
7.3.1 Measuring mode
A monotonic equivalence point titration can be carried out with four different
types of measurement:
• potentiometric pH measurement ( MET_PH*)
• potentiometric voltage measurement ( MET_U*)
• amperometric measurement with selectable polarization voltage ( MET_UPOL*)
• voltametric measurement with selectable polarization current
(
MET_IPOL*)
7.3.2 Reagent addition and measurement acceptance
Reagent addition is defined by laying down the size of the constant volume
increments and the dosing speed. The addition thus does not have any di-
rect relationship to the measuring behavior.
After the addition of a dosing increment the potential of the sample solution
is measured. Acceptance of a measurement in the measuring point list can
be drift-controlled or after a fixed waiting period. In drift-controlled meas-
urement acceptance the measurement drift of the measured potential must
be lower than a predefined amount for it to be accepted as a valid meas-
urement. If after a defined waiting period has elapsed this measurement drift
has not been undercut then the momentary measurement will be accepted
and included in the list of measuring points together with the corresponding
value for the volume.