Determination of Water Content in Sunblock Cream (Water Resistant) Using Karl Fischer Titration

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.

Special Information Concerning the Sample and the Methods

Due to the inadequate solubility of this substance in methanolic KF solvents the addition of a long-chain alcohol (e.g. decanol) or chloroform as solubiliser is necessary. 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 188021 Aquastar^® - CombiSolvent fats - Solvent for volumetric Karl Fischer titration with one component reagents for fats
or
25 mL / 25 mL 188009 / 803463 Aquastar^® - CombiMethanol / Decanol - solvent mixture for one component titration

Titration Parameters:
Stirring time: 60 - 120 sec.
Default titration settings, e.g.: I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size: 0.03 - 0.08 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 60 - 120 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 188016 Aquastar^® - Solvent oils & fats - Solvent for volumetric Karl Fischer titration with two component reagents for oils & fats
and
30 mL / 20 mL 188015 / 102445 Aquastar^® - Solvent / Chloroform - solvent mixture for two component titration

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: 0.03 - 0.08 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 60 - 120 seconds is recommended.