Karl Fischer Titration (KF titration)

Basic Principles and Instrumentation of Karl Fischer Nitration for moisture determination in solid and liquid samples is discussed.

1. Dr. Sajjad Ullah, ICS UoP

2. Dr. Sajjad Ullah, ICS UoP

3. KF oven
Thermal sample preparation
Dr. Sajjad Ullah, ICS UoP

4. Determination of water content is
important
Two Methods
A –Drying methods (drying ovens,
infrared lamps and infrared balances).
B –Titration methods : Specific to water
and rapid.
Dr. Sajjad Ullah, ICS UoP

5. KFT methods
Two Methods: based on I
2-providing principles
A–VolumetricKFT:I
2requiredforreactionisaddedfroma
buretteandwaterisquantifiedbasedonvolumeofKFR.
B–Coulometrictitrationmethods:I
2isproducedby
electrolysisofI
-
ionsandthequantityofelectricityusedin
electrolysisismeasured.
Advantages: High Water content (100 ppm to 100%.)
Disadvantages: Expensive, lengthy, KFR calibration
Advantages: Cheap, fast, absoulte method
Disadvantages: Low water content Water range 1 ppm to 5%
Dr. Sajjad Ullah, ICS UoP

6. How does a Volumetric Titrator work?
Thevolumetrictitratorperformsthefollowingthreekeyfunctions:
1)ItdispensesKFtitratingreagentcontainingiodineintothecell
usingtheburette
2)Itdetectstheendpointofthetitrationusingthedoubleplatinum
pinindicatorelectrode
3)ItcalculatestheendresultbasedonthevolumeofKFreagent
dispensedusingtheonboardmicroprocessor.
Dr. Sajjad Ullah, ICS UoP

7. How does a Coulometric Titrator work?
TheCoulometrictitratorperformsthefollowingthreekeyfunctions:
1)It generates iodine at the anode of the titration
cell, instead of dispensing KF reagent as in
volumetric titration.
2) It detects the endpoint of the titration using the
double platinum pin indicator electrode.
3) It calculates the end result based on the total
charge passed (Q), in Coulombs, using the on-
board microprocessor.
Dr. Sajjad Ullah, ICS UoP

8. Volumetric KFT
Principle-Thetitrimetricdeterminationofwateris
baseduponthequantitativereactionofwaterwithana
solutionofexcesssulfurdioxideandknowniodine
concentration(mgH
2O/mLKFR)inasuitablemedium
(methanol)inthepresenceofabase(bufferingagent)
thatreactswithhydrogenions.Thewatercontentis
determinedbymeasuringtheamountofiodine
consumedasaresultofreactionwithwaterinasample.
Dr. Sajjad Ullah, ICS UoP

9. Dr. Sajjad Ullah, ICS UoP

10. The Story of KFT Reaction
Bunson Reaction:
This reaction can be used to determine H
2O if SO
2is in excess
and H
2SO
4is neutralized by a base. Karl Fisher did that.
Karl Fischer , Angew. Chem. 48 (1935) 394 –396.
Dr. Sajjad Ullah, ICS UoP

11. Smith, Bryant and Mitchell Showed that:
The molar ratios were:
Inafirstpartialreactionwaterformsthe(hypothetical)pyridine
sulfurtrioxide,whichthenfurtherreactswithmethanol
Dr. Sajjad Ullah, ICS UoP

12. Verhoefand Barendrechtnoted that in the KF reagent it is
not the SO
2that functions as the reactive component, but rather
the intermediate monomethylsulfite ion that is formed from SO
2
and methanol:
this intermediate alkylsulfitesalt is then oxidized by iodine to an
alkylsulfatesalt. The reaction consumes H
2O.
hydroiodicacid salt
alkylsulfitesalt
alkylsulfatesaltalkylsulfitesalt
buffer
Verhoef, J. C. and Barendrecht, E. Mechanism and Reaction Rate of the
Karl-Fischer Titration Reaction. J. Electroanal. Chem. 1976, 71, 305-315
Dr. Sajjad Ullah, ICS UoP

13. Karl Fischer , Angew. Chem. 48 (1935) 394 –396.
KF Reagent
A solution of iodine and sulfur dioxide
in a mixture of pyridine and methanol.
Dr. Sajjad Ullah, ICS UoP

14. hydroiodicacid salt
alkylsulfitesalt
alkylsulfatesalt
alkylsulfitesalt
this intermediate alkylsulfitesalt is then oxidized by iodine to an alkylsulfatesalt.
The reaction consumes H
2O.
Dr. Sajjad Ullah, ICS UoP

15. Dr. Sajjad Ullah, ICS UoP

16. HOW to perform
a KF Titration? ? ?
Volumetric KFT
Dr. SajjadUllah, ICS UoP

17. Dr. Sajjad Ullah, ICS UoP

18. Dr. Sajjad Ullah, ICS UoP

19. Dr. Sajjad Ullah, ICS UoP

20. Homogenization of the KFR
Dr. Sajjad Ullah, ICS UoP

21. Dr. Sajjad Ullah, ICS UoP

22. Dr. Sajjad Ullah, ICS UoP

23. Dr. Sajjad Ullah, ICS UoP

24. Dr. Sajjad Ullah, ICS UoP

25. Dr. Sajjad Ullah, ICS UoP

26. Dr. Sajjad Ullah, ICS UoP

27. Dr. Sajjad Ullah, ICS UoP

28. Dr. Sajjad Ullah, ICS UoP

29. Coulometric KFT
IncoulometricKarlFischer,iodineisgenerated
electrochemicallyinsituduringthetitration.Wateris
quantifiedonthebasisofthetotalchargepassed(Q),as
measuredbycurrent(amperes)andtime(seconds),
accordingtothefollowingrelationship:
Q = 1C (coulomb) = 1A x 1S
Where 1mg H
2O= 10.72 C
Dr. Sajjad Ullah, ICS UoP

30. AdditionalDetails of the Technique
Effect of pH
Influence of Water Content
Influence of the organic solvent
Kinetics of KF reaction
Sample Size
Dr. Sajjad Ullah, ICS UoP

31. Influence of Water content
Thewatercontentoftheworkingmedium
influencesthestoichiometryoftheKFreaction.
Highwatercontent(aqueousmedia):
IfH
2Ocontent>1mol/L(18g/L)thenthereaction
behaviorchangestofavourtheBunsenreactionfor
aqueoussolutions.ThismeansthattwoH
2Oare
consumedforoneI
2oroneSO
2.
Dr. Sajjad Ullah, ICS UoP

32. Protic Solvent (methanol or ethanol): H
2O : I
2= 1:1
Reason: reactivity of alcohols plays a role—In methanol about
100%, in propanol approx. 80% and in butanol only approx. 50%
is present as sulfite ester.
Influence of Organic Solvent
Aprotic Solvent (DMF): H
2O : I
2= 2:1
Long chain alcohols: intermediate values (fractional values)
Dr. Sajjad Ullah, ICS UoP

33. Choice of Organic Solvent
AbestsolventisonethatassuresStoichiometryofKFreaction
anddissolvebothReactantandproductofthereaction.
Methanol-thefirstnaturalchoice:
Knownstoichiometry,rapidreaction,Goodsolubiltyofmostsamplesbutsidereactionsmayoccur
2-methoxyethanol(ethyleneglycolmonomethylether):
SuitbaleforaldehydesandKetonessampleslittlesidereactions(esterification,acetal/ketalformation)occur
Long-chainalcohols(ethanol,propanol)
Bettersolubilizingagentsthanmethanolforlipophilicmolecules
Chloroform:
goodsolventforsolubilizingfatsandcanbeusedwithmethanol.Themethanolcontentshouldcompriseat
least25%ofthetotalvolume,preferably50%.100chloroformchangesthestoichiometryofKFReaction.
Formamide(forProteins):
improvesthesolubilityofpolarsubstancesandcanbemixedwithmethanol(70%methanol)forthe
determinationofwaterinproteins.
Dr. Sajjad Ullah, ICS UoP

34. Kinetics of the KF reaction
Cedergreninvestigated the KF reaction sequence and establish that
 the reaction rate increases as the concentrations of SO
2, I
2
and H
2O increase.
 The reaction is first order referring to each individual
component.
 For the rate constant K he used the equation :
And obtained the values
Dr. Sajjad Ullah, ICS UoP

35. VerhoefandBarendrechtconfirmedtheresultsofCedergrenbutat
thesametimefoundthatthereactionconstantKdependsonthepH
ofthesolution:
pH<5 logKincreaseslinearlywiththepH.
pH=5.5-8 thereactionrateisconstant
pH>8 thereactionrateagainincreasesslightly
(sidereactionsprobablyoccur).
Important:
FromtheincreasesinKunderacidicconditionstheauthorsconclude
thatitisnotSO
2,butthesulfitebasethatisthereactivecomponent.
Kinetics of the KF reaction…
Verhoef, J. C. and Barendrecht, E. Mechanism and Reaction Rate of the
Karl-Fischer Titration Reaction. J. Electroanal. Chem. 1976, 71, 305-315
Dr. Sajjad Ullah, ICS UoP

36. The rate of the reaction depends on the pH value of the solvent, or working
medium.
at pH = 5-8 the titration proceeds normally (OPTIMAL)
at pH< 5 the titration speed is very slow
at pH> 8 the titration speed is fast (side reaction-esterification-
produces water, diffuse end point.
Comments:
Highly acidic or basic samples need to be buffered to bring the overall
pH into that optimal (5-8) range.
Effect of pH
Verhoef, J. C. and Barendrecht, E. Mechanism and Reaction Rate of the
Karl-Fischer Titration Reaction. J. Electroanal. Chem. 1976, 71, 305-315
Dr. SajjadUllah, ICS UoP

37. What sample size should be used?
Dr. Sajjad Ullah, ICS UoP

38. What sample size should be used?
Dr. Sajjad Ullah, ICS UoP

39. How can Titrator performance be monitored?
Dr. Sajjad Ullah, ICS UoP

40. General Considerations
 Changingthemolecularsievesevery6weeksisappropriate
inthepresenceofmediumhumidity.
 Molecularsievecanberegeneratedat300degreeCfor24h.
 Cleantheplatinumpinsontheindicatorelectrodewithasoft
papertissue,scrubsoftlywithtoothpaste.Afterwards,flushit
withethanolormethanol.
 Ifdriftvlauesisveryhighduringpre-titration(conditioning),
changethemolecualrsives,checkleakge,ensurenosidereaction
orpHchangehasoccuredandthesampleissolubleinsolvent.
 Thecellsolutionshouldbereplacedafterapproximately30mLof
titranthavebeenusedinthecaseofcellsolutionswith20...25
mLofsolvent
Dr. Sajjad Ullah, ICS UoP

41. How to recognize a side reaction?
The following characteristics indicate the presence of a side reaction:
 High drift after the titration has been completed, slow
endpoint recognition or no endpoint found at all
 The water contents determined are not independent of the
sample weight
 The results are (depending on the type of side reaction) too
high or too low
 The water recovery rate found when spiking samples is not
within 100 ±3%
Dr. Sajjad Ullah, ICS UoP

42. The Possibilities of side reaction?
Dr. Sajjad Ullah, ICS UoP

43. Detection of END POINT in KFT

44. The Titration termination/control parametrs
•The Change in Potential (E)
•The Drift Criterion
•Rate of reagent addition
•Delay time

45. 1-Change in Potential Criterion

47. fundamentals_of_kfvolbrochuree.pdf

48. Inadditiontoapredefinedvoltage(orcurrent),acertaindriftvaluemustalsobe
achieved.ThedriftistheamountofKFreagentperunittimethatisconsumedtokeep
thetitrationcelldry.Ingeneral,thedriftvaluefortitrationcellstitratedtodrynessisin
theorderofafewμL/min.
2

49. 3. Rate of Reagent additon
TheTitrantadditonratedependson
 thedistancefromtheendpoint―the
closertheEndPoint,theslowerthe
additionrate
 thePotentialchangewitheachadditon

50. The Delay time
The Titraion is terminated when E remains below the end point for
a defined time (e.g 15 seconds) following the addition of a titrant
increment

51. Titration Termination
The titration is terminated when the conditions of the Termination Criteria have
been met. The default Termination Criterion is mV value, in which the titration is
terminated after the mV value remains below the end point potential for the
selected stability time.

54. Additional Details of the Technique
Effect of pH
Influence of Water Content
Influence of the organic solvent
Kinetics of KF reaction
Sample Size

55. Influence of Water content
Thewatercontentoftheworkingmedium
influencesthestoichiometryoftheKFreaction.
Highwatercontent(aqueousmedia):
IfH
2Ocontent>1mol/L(18g/L)thenthereaction
behaviorchangestofavourtheBunsenreactionfor
aqueoussolutions.ThismeansthattwoH
2Oare
consumedforoneI
2oroneSO
2.

56. Protic Solvent (methanol or ethanol): H
2O : I
2= 1:1
Reason: reactivity of alcohols plays a role—In methanol about
100%, in propanol approx. 80% and in butanol only approx. 50%
is present as sulfite ester.
Influence of Organic Solvent
Aprotic Solvent (DMF): H
2O : I
2= 2:1
Long chain alcohols: intermediate values (fractional values)

57. Choice of Organic Solvent
AbestsolventisonethatassuresStoichiometryofKFreaction
anddissolvebothReactantandproductofthereaction.
Methanol-thefirstnaturalchoice:
Knownstoichiometry,rapidreaction,Goodsolubiltyofmostsamplesbutsidereactionsmayoccur
2-methoxyethanol(ethyleneglycolmonomethylether):
SuitbaleforaldehydesandKetonessampleslittlesidereactions(esterification,acetal/ketalformation)occur
Long-chainalcohols(ethanol,propanol)
Bettersolubilizingagentsthanmethanolforlipophilicmolecules
Chloroform:
goodsolventforsolubilizingfatsandcanbeusedwithmethanol.Themethanolcontentshouldcompriseatleast25%ofthetotal
volume,preferably50%.100chloroformchangesthestoichiometryofKFReaction.
Formamide(forProteins):
improvesthesolubilityofpolarsubstancesandcanbemixedwithmethanol(70%methanol)forthedeterminationofwaterin
proteins.

58. Kinetics of the KF reaction
Cedergreninvestigated the KF reaction sequence and establish that
 the reaction rate increases as the concentrations of SO
2, I
2
and H
2O increase.
 The reaction is first order referring to each individual
component.
 For the rate constant K he used the equation :
And obtained the values

59. VerhoefandBarendrechtconfirmedtheresultsofCedergrenbutat
thesametimefoundthatthereactionconstantKdependsonthepH
ofthesolution:
pH<5 logKincreaseslinearlywiththepH.
pH=5.5-8 thereactionrateisconstant
pH>8 thereactionrateagainincreasesslightly
(sidereactionsprobablyoccur).
Important:
FromtheincreasesinKunderacidicconditionstheauthorsconclude
thatitisnotSO
2,butthesulfitebasethatisthereactivecomponent.
Kinetics of the KF reaction…
Verhoef, J. C. and Barendrecht, E. Mechanism and Reaction Rate of the Karl-Fischer
Titration Reaction. J. Electroanal. Chem. 1976, 71, 305-315

60. The rate of the reaction depends on the pH value of the solvent, or working
medium.
at pH = 5-8 the titration proceeds normally (OPTIMAL)
at pH< 5 the titration speed is very slow
at pH> 8 the titration speed is fast (side reaction-esterification-
produces water, diffuse end point.
Comments:
Highly acidic or basic samples need to be buffered to bring the overall
pH into that optimal (5-8) range.
Effect of pH
Verhoef, J. C. and Barendrecht, E. Mechanism and Reaction Rate of the Karl-Fischer
Titration Reaction. J. Electroanal. Chem. 1976, 71, 305-315

61. What sample size should be used?

62. What sample size should be used?

63. How can Titrator performance be monitored?

64. General Considerations
 Changingthemolecularsievesevery6weeksisappropriate
inthepresenceofmediumhumidity.
 Molecularsievecanberegeneratedat300degreeCfor24h.
 Cleantheplatinumpinsontheindicatorelectrodewithasoft
papertissue,scrubsoftlywithtoothpaste.Afterwards,flushit
withethanolormethanol.
 Ifdriftvlauesisveryhighduringpre-titration(conditioning),
changethemolecualrsives,checkleakge,ensurenosidereaction
orpHchangehasoccuredandthesampleissolubleinsolvent.
 Thecellsolutionshouldbereplacedafterapproximately30mLof
titranthavebeenusedinthecaseofcellsolutionswith20...25
mLofsolvent

65. How to recognize a side reaction?
The following characteristics indicate the presence of a side reaction:
 High drift after the titration has been completed, slow endpoint
recognition or no endpoint found at all
 The water contents determined are not independent of the
sample weight
 The results are (depending on the type of side reaction) too
high or too low
 The water recovery rate found when spiking samples is not
within 100 ±3%

66. The Possibilities of side reaction?