Determination of Water Content in Extracts, Aqueous drops Using Karl Fischer Titration

Product Group

Cosmetics, Pharmaceuticals

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.

Pharmaceuticals

Pharmaceutical products are often characterized by complex formulations. Difficulties observed during Karl Fischer determination are often caused by the limited solubility. In some cases side reactions have to be considered. In dependance of composition and properties of the formulations, various measures are necessary for an undisturbed Karl Fischer determination. In pharmaceutical guidelines (USP, Ph Eur, DAB) the Karl Fischer titration is described as common method for water determination. For some substances special procedures can be found. The determination of mass loss as method for water determination is not recommended.

Special Information concerning the sample and the methods

Drops (e.g. cough-drops) and extracts on an aqueous or alcoholic basis are easily soluble in methanolic KF solvents and can be titrated according to volumetric standard methods with one or two component reagents. Due to the relatively high water content sample sizes of between 40 mg and 100 mg are recommended. The coulometric method is not suitable.

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
or
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: drift < 20 µL/min

Sample size:
0.04 - 0.1 mL

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 1 mL syringe with hollow needle or microlitre syringe (exact sample weight determination by weighing of syringe before and after injection) and the titration is started.

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

Sample size:
0.04 - 0.1 mL

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 1 mL syringe with hollow needle or microlitre syringe (exact sample weight determination by weighing of syringe before and after injection) and the titration is started.

Materials

     
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