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Determination of Water Content in Liquorice 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 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. Liquorice should be well ground prior to analysis. Titration is carried out under the addition of formamide at 50 °C. The use of a homogeniser increases solubility. As an alternative to the direct determination it is possible to dissolve the sample externally in formamide. For the KF determination an aliquote is then withdrawn. The result must be corrected for the blank value of the solvent. Due to the low water content the use of titrants with a low factor is recommended. The coulometric method can only be applied after external dissolution of the sample in formamide and is therefore 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
30 mL 188009 Aquastar™ - CombiMethanol - Solvent for volumetric Karl Fischer titration with one component reagents, max. 0.01 % water
and
20 mL 109684 Formamide - as solubiliser

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

Sample size:
0.3 g

Procedure:
The titration medium is first placed into the cell. After heating up to 50°c the titration medium is titrated dry by means of the titrant. Then the well-crushed sample 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 at least 5 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
30 mL 188015 Aquastar™ - Solvent - Solvent for volumetric titration with two component reagents
and
20 mL 109684 Formamide - as solubiliser

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

Sample size:
0.3 g

Procedure:
The titration medium is first placed into the cell. After heating up to 50°C the titration medium is titrated dry by means of the titrant. Then the well-crushed sample 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 at least 5 minutes is recommended.

Materials

     
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