Guide line
935 USP
Type Karl Fischer titration
Coloarimatry and volumetry titration
Colarimatry titration because use of a electromagnetic filed
Volumetric titration
There is a manually titration (classical method like In burette fill kf reagent and conical flask fill a Methanol see the end point straw yellow colour)
KF Reagent
It is a dark brown colour
Photosensitive
Moisture sensitive so after use cap would packed carefully
Store : Dry and dark place
Composite : Methanol,SO2,I2, pyridine or Imidazole
Reaction
SO2 + I2 + H2O = HI + SO3
SO3 + C5H5N = C5H5 N SO3
C5H5 N SO3 + C2H5 = C2H5 N SO3 C2H5
Volt use
15-20 V as on neutral
150 -200 V endpoint detection
Endpoint
Strow pale Yellow color
Indicator
Self indicator
Drift
Background Moisture call
Example vessel moisture
Role PH in Karl Fischer Reaction
Kf reaction depends on the pH value of the solvent. When pH is
between 5 and 8, the titration proceeds normally. However, when the pH is lower than 5,
titration speed is very slow. On the other hand, when pH higher is than 8, titration rate is fast, but
only due to an interfering esterification side reaction which produces water, resulting in an
vanishing endpoint. Thus, the optimal pH range for the Karl Fischer reaction is from 5 to 8, and
highly acidic or basic samples need to be buffered to bring the overall pH into that range.
