Determination of Water Content in Sunflower Oil Using Karl Fischer Titration

Description

GENERAL INFORMATION CONCERNING THE PRODUCT GROUP

Foodstuffs

Foodstuffs encompass the most diverse products. Depending on whether carbohydrate-rich, fatty or protein rich substances are under investigation, different working techniques are favourable. Complex matrices that dissolve slowly, or where the water can only be slowly extracted, necessitate the use of solubilisers. In addition, titration under heating and the application of a homogeniser to accelerate water release are expedient.

SPECIAL INFORMATION CONCERNING THE SAMPLE AND THE METHODS

Due to the inadequate solubility of this substance in methanolic KF solvents the addition of solubilisers (e.g. chloroform) or utilisation of specific KF solvents for fats (e.g. CombiSolvent fats) is necessary. Due to the low water content of the sample the use of a titrant with low factor is recommended. The water content in sunflower oil may be determined both, by the volumetric as well as the coulometric KF method.

Titration One Component System

Reagents:

Titrant
Aquastar^® – CombiTitrant 5 – One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 5 mg water

Solvent
50 mL  Aquastar^® – CombiSolvent fats – Solvent for volumetric Karl Fischer titration with one component reagents for fats

Titration Parameters:
Stirring time: 60 sec.
Default titration settings, e.g.:
I(pol) = 20 – 50 µA, U(EP) = 100 – 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
5 – 10 mL

Procedure:
The titration medium is first placed into the titration cell and titrated dry by means of the titrant. Then the sample is added with a syringe without hollow needle (exact determination through weighing of syringe before and after injection) or volumetric pipette and after a stirring time of 60 seconds the titration is started. It is possible to dissolve approx. 10 g oil before the KF solvent needs to be changed.

Coulometry with Diaphragm

Reagents:

Catholyte
5 mL  Aquastar^® – CombiCoulomat frit – Coulometric Karl Fischer reagent for cells with diaphragm

Anolyte
70 mL  Aquastar^® – CombiCoulomat frit – Coulometric Karl Fischer reagent for cells with diaphragm
and
30 mL  Decanol – as solubiliser

Titration Parameters:
Default coulometer settings for cell with diaphragm:
For end point indication, e.g.:
I(pol) = 5 – 10 µA, U(EP) = 50 – 100 mV
Stop criterion: drift < 10 µg/min

Sample size:
1 mL

Procedure:
The Karl-Fischer reagent is placed into the cathode and anode compartment of the titration cell with diaphragm. The coulometer is started and the solvent is titrated dry. After preliminary titration and stabilisation of drift the sample is injected into the titration cell with a syringe (exact sample weight determination by weighing of syringe before and after injection) and the water determination is started.

Coulometry without Diaphragm

Reagents:

Working medium:
80 mL Aquastar^® – CombiCoulomat fritless – Coulometric Karl Fischer reagent for cells with or without diaphragm
and
20 mL Decanol – as solubiliser

Titration Parameters:
Default coulometer settings for cell without diaphragm:
For end point indication, e.g.:
I(pol) = 5 – 10 µA, U(EP) = 50 – 100 mV
Stop criterion: drift < 10 µg/min

Sample size:
1 mL

Procedure:
The Karl-Fischer reagent is placed into the titration cell without diaphragm. The coulometer is started and the solvent is titrated dry. After preliminary titration and stabilisation of drift the sample is injected into the titration cell with a syringe (exact sample weight determination by weighing of syringe before and after injection) and the water determination is started.