Karl_Fischer_Titration_Drift_and_Sample_Size_Optimization__1709201648.pdf

Karl Fisher Titration

1. Karl Fischer Titration
Merck KGaA
Darmstadt,Germany

2. Agenda 4
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons for unstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

3. Agenda 6
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons for unstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

4. Chemical reaction:
H
2O + I
2+ SO
2+ 3 RN + ROH → (RNH)SO
4R + 2(RNH)I
Karl Fischer
Karl Fischer is an analytical technique used to measure the moisture (water) content in
solid, liquid or gases.
Karl Fischer reagent consists of
•Iodine, (I
2reacts with water 1:1)
•Sulfur dioxide,
•a base and
•a solvent, such as methanol
7
The solvent (methanol) is involved in the reaction.
50 % of the solvent must be methanol
A suitable base (RN) keeps the pH value between
5.5 –8
In the past: Pyridine
Today: Imidazole
Mettler Toledo solution for water
content determination from 1 ppm to
100 %.

5. Agenda 8
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons for unstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

6. Difference between Volumetric and Coulometric titration 1/2 9
Volumetric Method
Iodine It is added by burette
(as titrant) during
titration.
CalculationTitrant consumption
Technique
is suitable
Samplehaving water
content from
100 ppm to 100 %
Direct
titration:
Solid, liquid and
gaseous samples
Burette –Titrant
(KF Reagent)
Suitable
solvent (most
of the time it is
Methanol) and
Sample of
interest
Double pin
platinum
electrode -
Measurement

7. Difference between Volumetric and Coulometric titration 2/2 10
Coulometric Method
Iodine It is electrochemically generated by the generator cell during titration.
Calculation generated current.
Technique is suitableFor the Samples with low water content from 1 ppm up to 5 %
Direct titration Liquid and gaseous samples
Generator cell
1.With Diaphragm
2.Without
Diaphragm
Double pin
platinum
electrode -
Measurement

8. 11
Coulometrictitration –Generator Cell
With or without diaphragm
– +
– +
Anolyte
Catholyte
Anolyte

9. Agenda 12
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons for unstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

10. What is Drift?
The drift is amount of water (atmospheric humidity) enter into the titration
stand per minute
13
•High drift Pretitrationmode
•Low and steady/stable drift
“ready” (Standby) mode

11. What is Drift?
Since it is a closed system, where are the water (air humidity)
entry points ?
14
The titration stand is never 100% tight
Automatic drift compensation in the result calculation

12. Automatic drift compensation 15
Example:
Drift: 5 ug/min
Titration time: 2 min
Sample result
= water determined –(5ug/min x 2min)
= water determined –10ug
Ideal conditions for standby:
E ≤ 100 mV
Drift ≤ 25 µg/min
Sample result = total amount of water determined –(drift * titration time)
Display of instrument screen
represents stable / steady drift and
ready for std/splanalysis.

13. Agenda 16
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons for unstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

14. Reasons for unstable drift… 17
Titration stand is not
protected from
atmospheric humidity
Root cause of unstable drift at two different
conditions
Pre titration After Titration
1. Incomplete
dissolution of sample/
extraction of water
from sample
2. Side reaction of
sample with KF
reagent

15. Agenda 18
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons for unstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

16. How to achieve good drift… 1/2
Pre titration condition
19
For internal use -Confidential
Root
cause
Good practice/ Troubleshooting
Volumetric KF titration Coulometric KF titration
Moisture
entering in
titration
vessel /
Moisture
present in
cathode
compartme
nt and
diaphragm
-Replace molecular sieves and
silica gel in drying tube
-Check whether titration stand is
completely tight.
-Grease the tapered joints
-Condition Titration stand –
Gentlyshake titration vessel
-Replace anolyte
-Level of anolyte should be higher than
that of the catholyte(3-5mm)
-Clean titration cell and generator
electrode and dry at 50 –80 °C. Let it
cool downovernight before reuse.
-Check whether titration stand is
completely tight.
Oven:
-Replace silica gel and molecular sieve in
the gas drying unit
Don't Do not install titrator close to air flow. E.g. Air-conditioner,
Fume wood

17. How to achieve good drift… 2/2
After sample titration
20
Root causeGoodpractice/ Troubleshooting
Volumetric KF titration Coulometric KF titration
Incomplete
dissolution
of sample/
extraction
of water
from
sample
Use longer mixing time or different
solvents which dissolves the
sample or extracts the water quicker.
-Heating oventechnique: water is
not completely vaporized
-Increase oven temperature
-Increase vaporization time, e.g.
increase t(max)
Use longer mixing timeor suitable
solvents to dissolve the samples
Heating oventechnique: water is not
completely vaporized
-Higher oven temperature
-Increase vaporization time, e.g.
increase t(max)
Side
reaction of
sample with
KF reagent
Use suitable reagent for example
For ketone sample, K-reagents are
used.
Use different method, e.g. external
extraction, drying oven, etc.
-Use a different method

18. Agenda 21
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons for unstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

19. How to decide correct sample size? 1/4
Determine graphically the amount of sample for a water content in the range from 1ppm to
100%
22
Manual way of calculating using below scale
Expected water content
Sample size
Coulometric
detection range
Volumetric
detection range
How to calculate optimum
sample size?
1. Start from the optimum point
10 mg for volumetric KF,
1 mg for coulometric KF
2. Connected by a straight line to
the expected water content.
3. The intersection point of this
line with the "Amount of
sample"

20. How to decide correct sample size? 2/4
Calculate optimum sample size
required for 1000 ppm water content
for Volumetric KF titration?
100%
1%
10%
1000ppm
100ppm
10ppm
1ppm
0.01g
1g
10g
100g
0.1g
1g
100g
10g
1mg
10mg
100mg
1000mg
Volu
Coulo
23
Content Sample size Water amount
Given :
Expected water content of sample = 1000
ppm
Calculation Steps:
1. Volumetric optimum point on scale = 10 mg
2. Connect a line from 10 mg of volumetric
detection point to expected water content i.e.
1000 ppm
3. Intercept point on sample size scale will
provide suitable sample size required for
analysis. In this case it is approx. 5 g.

21. How to decide correct sample size? 3/4
Calculate optimum sample size
required for 100 ppm water content for
Coulometric KF titration?
100%
1%
10%
1000ppm
100ppm
10ppm
1ppm
0.01g
1g
10g
100g
0.1g
1g
100g
10g
1mg
10mg
100mg
1000mg
Volu
Coulo
24
Content Sample size Water amount
Given :
Expected water content of sample = 100 ppm
Calculation Steps:
1. Coulometric optimum point on scale = 1 mg
2. Connect a line from 10 mg of volumetric
detection point to expected water content i.e.
100 ppm
3. Intercept point on sample size scale will
provide suitable sample size required for
analysis. In this case it is approx. 12 g.

22. How to decide correct sample size? 4/4 25
MT offers built-in
sample size
calculator for routine
samples
Method Start
Click on option
'More' which is
located at on the
ribbon of display
screen
Click on option
'Sample size
calculation'
Enter
expected
water
content and
required
unit
Click on
Calculate
Flowchart to explain 'how to
use inbuilt sample size
calculation'?

23. Built in calculator in detail…
26
Likewise we can make for 10 mL burette volume what will be the limits to use it for
further calculationof sample size.
Calculation steps which is incorporated in algorithm during calculating sample size by
instrument:
1.Titrant Consumption (30 –70 %)
To get accurate and precise measurement result, MT recommends to choose sample
size which will consume titrant with volume 30 –70 % of burette size
If we take 5 mL as burette size, then volume of titrant consumption should be in the
range of 1.5 mL to 3.5 mL.
Example:
Titrant concentration = 5 mg/mL
Burette size = 5 mL
Upper limit = 3.5 mL x 5 mg/mL = 17.5 mg (required water content)
Lower Limit = 1.5 mL x 5 mg/mL = 7.5 mg (required water content)

24. Built in calculator in detail… with example!
Calculate the optimum sample size for volumetric Karl Fischer titration when
Burette volume= 5 mL,
Titrant concentration = 5 mg/mL,
Expected water content = 2% (20 mg/g)
20 mg in 1 g
27
Lower limit
(7.5 mg of water)
Upper limit
(17.5mg of water)
20 mg water = 1 g sample
7.5 mg = 'X'
20 mg water = 1 g sample
17.5 mg = 'X'
After cross multiplication,
'X' = 0.375 g
After cross multiplication,
'X' = 0.875 g
Volumetric Karl Fischer Titrator

25. Built in calculator for Coulometric KF titrator
Calculate the optimum sample size for Coulometric Karl Fischer titration:
Expected water content = 750 ppm (0.750 mg/g)
0.750 mg in 1 g
28
Lower limit
(0.5 mg ofwater)
Upper limit
(2mg of water)
0.75 mg water = 1 g sample
0.5 mg = 'X'
0.75 mg water = 1 g sample
2 mg = 'X'
After cross multiplication,
'X' = 0.67 g
After cross multiplication,
'X' = 2.67 g
CoulometricKarl Fischer Titrator

26. Agenda 29
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons forunstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

27. Frequently asked questions
1. pH Shift of the titration solution -Avoid values less
than 5.5 and greater than 8
Solution:
Adjust acidic and basic samples by adding buffering
agents
For acidic sample: imidazole,
For basic sample: salicylic acid)
30
2. Our Karl Fischer says 'OVER TITRATION' and the reagent is turning really dark. Why?
Solution:
"Over Titration" means that the reagent "anolyte" has released more then enough iodine to
consume the amount of moisture that exists inside the vessel.
Over titration is common sign of coated sensor pins. Use paper tower to clean the double
pins.
Sensor double pins

28. Frequently asked questions 31
3. Should I use KF grease?
Solution:
"Some vessels are designed differently and have ground glass fitting instead of screw on
caps . As we are working with ground glass fittings, then it is require to use KF grease to seal
the fittings.
4. How can I make sure my instrument is giving me good results?
Solution:
Check periodically with water standards & Sodium Tartrate Dihydrate(Vol. KF). It can help
one verify that the instrument is performing properly.
Ground glass fittings

29. Agenda 32
1Introduction
2KarlFischer Titration
3Difference between Volumetric and Coulometrictitration
4What is Drift?
5Reasons for unstable drift
6How to achieve good drift /overcome unstable drift
7Optimum Sample size for Karl Fischer Titration
8FAQ
9Q&A

30. Thank You
34