Determination of Water Content in Saccharose (adherent moisture) Using Karl Fischer Titration

Product Group

Foodstuffs

General Information concerning the product group

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

The dissolution of carbohydrates in methanolic KF solvents is often inadequate. For complete dissolution of the sample therefore the addition of formamide is necessary. However, the proportion of formamide should not exceed 50 %. Additionally, titration under warm conditions (50 °C) is favourable. With some types of sugar, however, heating leads to disintegration. With this substance, often only the adherent moisture is determined, since surface moisture affects the pourability of the material. The dissolution of the sample should therefore be avoided. Titration should thus be carried out by means of non-polar solvents in the solvent(e.g. addition of chloroform). At the same time instrument settings should be adjusted for a short titration time (short switch-off time or high stop drift). Due to the low water concentration the use of titrants with low factors is recommended. The coulometric method can only be applied after external dissolution of the sample in chloroform and is therefore less recommended.

Titration one component system

Reagents:

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

Solvent
20 mL 188008 Aquastar™ - CombiSolvent - Methanol-free solvent for volumetric Karl Fischer titration with one component reagents
and
40 mL 102445 Chloroform - to prevent dissolution of the sample

Titration Parameters:
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion for fast titration: drift < 40 µL/min

Sample size:
5 g

Procedure:
The titration medium is first placed into the cell and titrated dry by means of the titrant. Then the sample is added from a weighing boat (exact sample weight determination by weighing of weighing boat before and after addition) and the titration is started. Titration is carried out to fast end point.

Titration two component system

Reagents:

Titrant
188011 Aquastar™ - Titrant 2 - Titrant for volumetric titration with two component reagents, 1 mL = approx. 2 mg water

Solvent
25 mL 188016 Aquastar™ - Solvent oils & fats - Solvent for volumetric Karl Fischer titration with two component reagents for oils & fats
and
25 mL 102445 Chloroform - to prevent dissolution of the sample

Titration Parameters:
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion for fast titration: drift < 40 µL/min

Sample size:
5 g

Procedure:
The titration medium is first placed into the cell and titrated dry by means of the titrant. Then the sample is added from a weighing boat (exact sample weight determination by weighing of weighing boat before and after addition) and the titration is started. Titration is carried out to fast end point.

Materials

     
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