Determination of Water Content in Stearic acid Using Karl Fischer Titration

Product Group

Carboxylic acids

General Information concerning the product group

Carboxylic acids

Most carboxylic acids can be analysed relatively easily following standard KF titration methods. Due to their weakly acidic properties they exhibit only a slight effect on the pH of the KF solution. Only the stronger acids require neutralisation or buffering of the solvent prior to measuring. This is achieved by the use of organic amines. In some cases esterification with methanol results in the formation of water. This potential interference should especially be taken into account with coulometric determination. In the event of solubility problems solubilisers may be added. With some substances, only the adherent moisture can be determined by volumetric titration, or alternatively KF oven technology may be employed.

Special Information concerning the sample and the methods

Stearic acid only slightly dissolves in methanolic solvents. Therefore a special KF solvent for fats (as example CombiSolvent fats) is necessary. Also the use of a homogeniser is recommended.

Titration one component system

Reagents:

Titrant
188002 CombiTitrant 2 - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 2 mg water

Solvent
null 188021 CombiSolvent fats - Solvent for volumetric Karl Fischer titration with one component reagents for fats in foodstuff

Titration Parameters:
Stirring time: 300 sec.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
1 - 2g

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 extraction of the sample a stirring time of 300 seconds and the use of a homogeniser is recommended.

Materials

     
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