Determination of Water Content in Oil of oranges Using Karl Fischer Titration

Product Group

Cosmetics, Foodstuffs

General Information concerning the product group

Cosmetics

Cosmetics on an aqueous and alcoholic basis can be titrated without problems according to the Karl Fischer (KF) method. Due to the often high water concentration of the emulsions small samples are required. The accuracy of analysis is determined through exact sampling, weighing and adding. The coulometric method is unsuitable for most emulsions. Fatty and oily preparations are insoluble in methanolic KF solvents and require the addition of a solubiliser, or respectively titration with specific KF solvents for oils and fats.

Foodstuffs

Foodstuffs encompass the most diverse products. Depending on whether carbohydrate-rich, fatty or proteinrich 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

Citrus oils contain aldehydes as additional constituents. Because aldehydes react with methanol under formation of water, methanol-free KF solvents must be used for the KF titration. The volumetric one component titration with CombiSolvent is preferred. Due to the low water content a titrant with low factor should be used. The coulometric method is possible, but due to side reactions less recommended.

Titration one component system

Reagents:

Titrant
188005 Aquastar™ - CombiTitrant 5 - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 5 mg water
or
188002 Aquastar™ - CombiTitrant 2 - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 2 mg water

Solvent
50 mL 188008 Aquastar™ - CombiSolvent - Methanol-free solvent for volumetric Karl Fischer titration with one component reagents

Titration Parameters:
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion for fast titration: drift < 30 µL/min

Sample size:
5 g

Procedure:
The titration medium is first placed into the titration cell and dried by means of the titrant. Then the sample is added with a syringe (exact sample weight determination by weighing of syringe before and after injection) or volumetric pipette and the titration is started. It is possible to analyse approx. 10 g oil before the KF solvent needs to be changed.

Coulometry with diaphragm

Reagents:

Catholyte
5 mL 109255 Aquastar™ - CombiCoulomat frit - Coulometric Karl Fischer reagent for cells with diaphragm

Anolyte
100 mL 109255 Aquastar™ - CombiCoulomat frit - Coulometric Karl Fischer reagent for cells with diaphragm

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 for fast titration: drift < 20 µg/min

Sample size:
0.3 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 pretitration 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. Titration is carried out to fast end point.

Coulometry without diaphragm

Reagents:

Working medium
100 mL 109257 Aquastar™ - CombiCoulomat fritless - Coulometric Karl Fischer reagent for cells with or without diaphragm

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 for fast titration: drift < 20 µg/min

Sample size:
0.3 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 pretitration 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. Titration is carried out to fast end point.

Materials

     
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