Metrohm 796 Titroprocessor - Manual (Page 117)

7. Titration and measuring modes
796 Titroprocessor, Instructions for use 111 111
7.6 KFT Karl Fischer titrations
Application:
The KFT modes are rapid titration modes for the volumetric determination of
moisture according to the Karl Fischer method.
Their typical feature is controlled reagent dosing depending on the control
difference (actual value – endpoint) with the aim of reaching the preset value
as quickly and accurately as possible. Overshooting is virtually eliminated.
Important: It is absolutely necessary to take care that all work is carried out
in the absence of water. The titration must be carried out in a tightly sealed
titration cell so that atmospheric moisture cannot affect the titration. If this
should not be possible, e.g. if a sample changer is being used, then a blank
value should always be determined and subtracted from the actual reagent
consumption when the results are being calculated.
U[mV]
V[mL]
t[s]
EP
V[mL]
Initial
addition
Continuous
addition
addition
Control
range
I[µA]
V[mL]
EP
KFT Ipol
KFT Upol
KFT: Karl Fischer titration
Reagent addition:
controlled addition,
depending on the control
difference
(actual value – endpoint)
Switch-off criterion:
drift-controlled and/or after
waiting period
7.6.1 Measuring mode
A Karl Fischer titration can be carried out with two different types of meas-
urement:
• voltametric measurement with selectable polarization voltage
(
KFT_IPOL*)
• amperometric measurement with selectable polarization current ( KFT_UPOL*)