1. Determination of Water by the Karl Fischer Titration:
Theory

2. Program
Motivation
Volumetric KF titration one an two-component reagents resolution and detection limits
Coulometric KF titration cell with or without diaphragm resolution and detection limits
Indication, control algorithm, termination parameters
KF titration: important points
Support

3. Why measure water or moisture?
Sugar: too much moisture
will not flow
Flour: too little moisture
dust explosion
Butter: max 16.5% water content
by law
Drugs: too much moisture
decomposition
Compact Disc: too much moisture
bad music quality
Brake Fluid: too much water
brake do not work
Kerosene: too much water
blocked tubing

4. Methods for the Determination of Water
Drying oven
Balance with IR /Halogen / Microwave heater
Thermogravimetry / DSC
Spectroscopy (IR, MS)
Chromatography
Karl Fischer Titration

5. Karl Fischer Titration: Why?
Fast (e.g minutes)
Selective for water
Accurate and precise (0.3% srel)
Wide measuring range : ppm to %
Coulometric KF
Volumetric KF

6. Karl Fischer German petrochemist, 1901 – 1958 Publication: 1935
Bunsen reaction: 2 H2O + SO2 + I2 = H2SO4 + 2 HI Pyridine happened to be around in the Lab

7. H2O + I2 + SO2 + 3RN + ROH ----->(RNH)SO4R + 2(RNH)I
KF Titration
KF Reaction
SO2 + RN + ROH > (RNH)SO3R
a sulfite compound
(RNH)SO3R + H2O + I2 + 2RN > (RNH)SO4R + 2(RNH)I
a sulfate compound
Summary
H2O + I2 + SO2 + 3RN + ROH ----->(RNH)SO4R + 2(RNH)I
The solvent (generally methanol) is involved in the reaction
A suitable base keeps the pH 5 - 7

8. Solvent pH range optimal pH 5 - 7 buffer needed side reactions optimal
slow
side reactions pH
log K 2 4 6 8 10

9. Volumetric / Coulometric Titration
Volumetric Karl Fischer Titration Iodine is added by burette during titration.
Water as a major component: 100 ppm % + -
Coulometric Karl Fischer Titration Iodine is generated electrochemically during titration.
Water in trace amounts: 1 ppm - 5 %

10. Volumetric KF Titration
Iodine is added by burette during titration.
Water as a major component: 100 ppm %

11. Volumetric KF Titration
One - component reagent
Titrant: I2 , SO2, imidazole, methanol and diethylene glycol monoethyleter
Solvent: Methanol
Two - component reagent
Titrant: I2 and Methanol
Solvent: SO2, Imidazole, Methanol
-> fast reaction, chemically stable, higher cost

12. Volumetric KF Reagents
Titrant Concentration
1-2-5 mg H2O/mL
Titer stability
-----> Check by Standardization
Standardization materials
Water 100%
Sodium tartrate %
Standard solution 5 mg/mL
Water Standard 1% (10 mg/g)

13. Air Humidity Air humidity: 0.5 - 3 mg water / 10 mL air
Tropical countries: Air conditioning
Well sealed titration cell
Conditioning of the titration stand
Protect titration stand, titrant and solvent from ingress of water.

14. Drift determination Drift determination 1 - 20 µg H20 / minute
The titration stand is not 100 % tight against air humidity.
Drift determination
The drift is the amount of water entering into the titration stand per minute.
µg H20 / minute
Automatic drift compensation in the result calculation.

15. Resolution and Detection Limit
Volumetric Karl Fischer Titration
Resolution of burette: 10,000 steps
Detection limit : 50 x Resolution
Burette size: mL
Titrant: 5 mg H20/mL
Resolution: 2.5 µg H20/step
Detection limit: 125 µg H20
For 5 g sample: 25 ppm
Titrant: 2 mg H20/mL
Resolution: 1 µg H20/step
Detection limit: 50 µg H20
For 5 g sample: 10 ppm

16. Coulometric KF Titration
Iodine is generated electrochemically during titration
Water in trace amounts: 1 ppm - 5 % - +

17. Coulometric KF Titration
Titration cell and reagents
Anode
Cathode + –
Generator electrode
Double platinum pin electrode
Anolyte
(sulfur dioxide, imidazole, iodide, different solvent for different application - methanol, ethanol with chloroform, octanol, ethyleneglycol )
Catholyte
(similar or modified solution)
Diaphragm

18. Coulometric KF Titration
Same reaction as volumetric KF Titration
but Iodine is produced just in time from iodide + – H+ - H I- I
Side reaction: Reduction of sulfur components.
After weeks, smells like mercaptans
Change catholyte every week! H2
2 H e-
Cathode
2 I-
I e-
Anode Iodine production by oxidation

19. 1 C = 1 A • 1 s Absolute method, no standardization!
Coulometry Theory
One Coulomb C is the quantity of charge transported by an electric current of one Ampere (A) during one second (s).
1 C = 1 A • 1 s Absolute method, no standardization!
Charles Augustin de Coulomb
To produce one mol of a chemical compound, using one electron, C are required.
2 I- ions react to form I2 which in turn reacts with water
1 mol of water (18g) is equivalent to 2 x C or C/mg water.

20. Filling the Titration Cell
Catholyte: Fill in 5 mL catholyte.
Anode + –
Cathode
Catholyte
Anolyte
Anolyte:
Fill in ~ 100 mL anolyte
The level of the anolyte should be
3 - 5 mm higher than the level of catholyte so
that the flow is from the anolyte compartment
to catholyte compartment.
 Low drift value
With stirring the level difference of anolyte
and catholyte will be stable.

21. Filling the Titration Cell
Anode + –
Cathode
Catholyte always contains water!
If the catholyte level is
higher or at the same level
as the anolyte,
there is a flow of moisture
into the anolyte compartment.
Catholyte
 High drift value
Anolyte

22. With or Without Diaphragm
What are the differences?

23. + – + – With or Without Diaphragm With Diaphragm Without Diaphragm I-
It is possible that iodine can go to the cathode
and convert to iodide. I- - I
Iodine is only in the anode
compartment and reacts
with water.

24. Without Diaphragm
Iodine I2 can go to the cathode and convert to iodide. – +
Prevention: - H+ H
Small cathode surface  less chance to contact iodine
high stirrer speed  iodine reacts faster with water I- - I
high iodine production speed  hydrogen protects cathode
Only a little less accurate for samples
with very low water content.
bigger sample  error has no effect

25. Without Diaphragm
The hydrogen produced at the cathode is a very good reducing agent. – I- - I H+ H
R-NO2
R-NH2 + H2O +
Easily reducible samples (nitro compounds) get reduced, which produces water.
 too high result
Not recommended for easily reducible samples: e.g. nitrobenzene, unsaturated fatty acids, etc.

26. Titration cell easier to clean.
Without Diaphragm
Titration cell easier to clean.
Long-term drift value more stable.
Only one reagent.
Titration cell without diaphragm is the standard set-up for: Hydrocarbons, halogenated hydrocarbons, alcohols, esters, ethers, acetamides, mineral oils, edible oils, ethereal oils
A little bit less accuracy for very small water content (< 50 µg/sample).
Not recommended for easily reducible samples: nitro compounds, unsaturated fatty acids, etc.

27. Resolution and Detection Limit
Coulometric Karl Fischer Titration + -
Resolution: 0.1 µg water
Detection limit: 5 µg water
for 5 g sample  1 ppm
Measuring range:
10 µg mg water/sample
1 ppm - 5 % water

28. Coulometry versus Volumetry
Repeatability
coulometry
Not suitable
for volumetry
srel > 5 %
srel %
srel < 0.5 %
volumetry
1 ppm
10 ppm
100 ppm
1000 ppm
1 %
10 %
100 %
Not suitable
for coulometry
srel < 0.5 %
srel %
srel > 5 %

29. KF Indication Principle (1/2)
Bivoltametric indication constant current at the double platinum pin electrode
==> polarization current (Ipol)
During titration:
I2 reacts with water
no free I2 in the solution
high potential
Ipol = 20µA
U = 650mV 2

30. KF Indication Principle (2/2)
Ipol = 20µA
U = 84mV 2
At endpoint
all water has reacted with I2
After the endpoint
free I2 in the solution
I2 is reduced to I- at the cathode
ionic conductivity occurs and the measured potential drops
potential change = endpoint
+ - e I2
I2 + 2e- -> 2 I-
2 I- -> I2 + 2e-
2I-

31. KF Control: Titrator Algorithm
Karl Fischer Fuzzy Logic Control DL31/38
No control band required
(typical 300 mV)
The titrant addition rate depends on:
the distance to the endpoint EP
the potential change/increment
Advantages:
Simpler control: Only two control parameters Vmin , Vmax (smallest/largest increment)
Faster, more accurate, and better precision even at low water content (toluene: n = 5, 115 ppm, srel 0.17% )
V/mL
E/mV
Control range EP
KF Classical
V/mL
E/mV EP
KF Fuzzy logic

32. KF Control: Termination Parameters (1/3)
Delay time
the actual potential is lower than the EP for a defined time after the last titrant increment
typical delay : sec
Note: Adapt the smallest increment to the drift and to the concentration of the titrant
E (mV) EP
15 s
t(s)

33. KF Control: Termination Parameters (2/3)
Drift (µg/min)
abs. drift stop
= 30 µg/min EP
Absolute drift stop
the actual drift is less then the predefined value
typical value : 30 g/min
Note: Adapt the value to the initial drift
t(s)

34. KF Control: Termination Parameters (3/3)
Drift (µg/min)
t(s)
Initial drift
Rel. Drift stop
= 20 µg/min
Relative drift stop
the sum of the initial and the relative drift has been reached
typical value : 15 g/min
independent from the initial drift and of titrant concentration
ideal with side reactions that cannot be suppressed otherwise

35. Karl Fischer Titration : Checks
Relevant points to be checked
System tightness : Check carefully
Ambient moisture : Drift determination
Stability of titrant : Standardisation
Side reactions : Check literature
Sample handling : Accuracy, precision
Free water only : Sample preparation

36. Complete Solution : Solutions and Support
Application brochures
Internet databases