7. KF titration methods
Coulometric KF titration
Iodine is generated in titration
cell (anodic oxidation)
Volumetric KF titration
Working medium & titrant
8. The main compartment of the titration cell
contains the anode solution plus the analyte.
1.alcohol (ROH),
2.a base (B),
3. SO2
4. I2.
A typical alcohol that may be used
is methanol or diethylene glycol monoethyl
ether, and a common base is imidazole.
9. The volumetric titration is based on the same
principles as the coulometric titration except that
the anode solution above now is used as the titrant
solution.
The titrant:
1. an alcohol (ROH),
2. base (B),
3. SO2
4. a known concentration of I2.
5. Pyridine has been used as the base in this case.
11. • in technical products
(oil, plastics and gases)
• in cosmetic products
• in pharmaceutical products
• in food industry
12. • The major disadvantage with solids is that
the water has to be accessible.
• Easily brought into methanol solution.
• KF is selective for water
Hinweis der Redaktion
invented in 1935 by the German chemist Karl Fischer
< pH 5: log K increases linearly with pH
reaction rate to low (low results)
5.5-7: optimum, reaction rate constant
>8: reaction rate increases slightly (side reactions probably occur)
Voltage: High as long as H2O in sample + I2 added
Once reaction turnover decreases, potential decreases
End point is not sufficient as criteria (titration would stop at signal at 88 sec)
-> Additionally drift as EP criteria
Drift <- water entering system