Determination of Water Content in Soft cheese 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 solubility of soft cheese in methanol is rather poor. During a stirring time of three to five minutes, it is, however, possible to fully extract the water. Titration under warm conditions (50 °C) and/or the use of formamide increase the release of water. Additionally, the use of a homogeniser is favourable. The non-homogeneous distribution of water as well as the small sample size require good homogenisation for KF titration prior to sampling. As an alternative, it is possible to carry out an external extraction with a suitable solvent. For the KF titration an aliquote of the sample is withdrawn. The result must be corrected for the blank value of the solvent.

Titration one component system

Reagents:

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

Solvent
50 mL 188009 Aquastar™ - CombiMethanol - Solvent for volumetric Karl Fischer titration with one component reagents, max. 0.01 % water

Titration Parameters:
Stirring time: 180 sec. (or 60 sec. with homogeniser)
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
0.1 g

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 sample weight determination by weighing of syringe before and after injection) and the titration is started. For complete dissolution of the sample a stirring time of 180 seconds 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

Solvent
50 mL 188015 Aquastar™ - Solvent - Solvent for volumetric titration with two component reagents

Titration Parameters:
Stirring time: 180 sec. (or 60 sec. with homogeniser)
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
0.1 g

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 sample weight determination by weighing of syringe before and after injection) and the titration is started. For complete dissolution of the sample a stirring time of 180 seconds is recommended.

Materials

     
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