1. Water content determination by Karl Fischer titration
Ivo Leito
University of Tartu

2. Karl Fischer (KF) titration
The primary method for determination of water content
Based on the oxidation-reduction reaction:

3. KF Titration Two types: We will look at volumetric KF titration only
Classical titration medium: Methanol (or solvent mixture)
Classical titrant: I2, SO2 and pyridine in methanol
Coulonometric
Titration medium: SO2, pyridine and some iodide in methanol
Iodine is generated electrochemically
We will look at volumetric KF titration only

4. End point determination
End point is determined by a small amount of unreacted iodine in solution
Usually voltammetrically

5. Titratnt titer (water equivalent)
Titrant water equivalent (milligrams of water per ml of titrant) is redetermined frequently
Every day or every second day
It is determined by titrating known amounts of water
@lisada, et analüüdi omadustest tulenevalt on titrandi tiiter väga ebapüsiv.

6. Equipment Karl Fischer titrator: Airtight titration vessel
Electrode for end-point determination
Solvent bottle
Titrant bottle
Piston burette for dispensing titrant
Septum for sample injection

7. Sequence of work (ISO 8534:1996 )
The solvent is titrated to the end-point
5-20 g of oil sample is weighed in a syringe to nearest 0.01 g.
The sample is injected into the titration cell
The empty syringe is weighed again to determine the mass of the oil sample.
When the sample has dissolved then the sample is titrated to the end-point
Concentration of water in the sample is calculated from the titration data.

8. ISO GUM Uncertainty estimation: Measurand, measurement equation
Measurand: Cwater, concentration of water in oil sample [mg/kg]
Vt: volume of titrant used for titration [ml]
Tt: the titer (water equivalent) of the titrant (mass of water per unit volume of titrant) [mg/ml]
ms: the sample mass [g]
1000 [g/kg] is the unit conversion factor

9. Sources of uncertainty
Mass measurement
Volumetric measurement
Titrant concentration
Precision of determination of the equivalence point
Contamination by atmospheric moisture
Interferences

10. Measurement equation for uncertainty calculation:
(5)
fr: Repeatability factor [unitless]
Value: 1
Uncertainty:
(6)

11. Uncertainty components and combined standard uncertainty
(5)

12. Data