Determination of Water Content in Chocolate Using Karl Fischer Titration

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

Chocolate contains a high proportion of fats and does not dissolve well in methanolic KF solvents. Therefore the addition of solubilisers (e.g. chloroform) or utilisation of specific KF solvents for fats (e.g. CombiSolvent fats) is necessary. Additionally, titration under warm conditions (50 °C) and/or the use of a homogeniser is favourable. The low water concentration of the sample requires the use of a titrant with a low factor. The coulometric method is not recommended here.

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 188021 Aquastar^® - CombiSolvent fats - Solvent for volumetric Karl Fischer titration with one component reagents for fats
or
25 mL / 25 mL 188009 / 102445 Aquastar^® - CombiMethanol / Chloroform - solvent mixture for one component titration

Titration Parameters:
Stirring time: 5 min.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
0.5 g (crushed)

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. For complete dissolution of the sample a stirring time of five minutes is recommended.

Titration Two Component System

Reagents:

Titrant
188010 Aquastar^® - Titrant 5 - Titrant for volumetric titration with two component reagents, 1 mL = approx. 5 mg water
or
188011 Aquastar^® - Titrant 2 - Titrant for volumetric titration with two component reagents, 1 mL = approx. 2 mg water

Solvent
25 mL 188015 Aquastar^® - Solvent - Solvent for volumetric titration with two component reagents
and
25 mL 102445 Chloroform - as solubiliser

Titration Parameters:
Stirring time: 5 min.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
0.5 g (crushed)

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. For complete dissolution of the sample a stirring time of five minutes is recommended.