Determination of Water Content in Formic 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

Formic acid undergoes rapid esterification in methanolic solutions. In addition, formic acid is oxidised by iodine. Water determination by Karl Fischer titration can only be carried out in methanol-free media and with small samples. Coulometric analysis is not possible.

Titration one component system

Reagents:

Titrant
188002 Aquastar^® - CombiTitrant 2 - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 2 mg water
or
188006 Aquastar^® - CombiTitrant 5 Keto - One component reagent for volumetric Karl Fischer titration of aldehydes & ketones, 1 mL = approx. 5 mg water

Solvent
50 mL 188008 Aquastar^® - CombiSolvent - Methanol-free solvent for volumetric Karl Fischer titration with one component reagents
or
50 mL 188007 Aquastar^® - CombiSolvent Keto - Solvent for volumetric Karl Fischer titration with one component reagents for aldehydes & ketones

Titration Parameters:
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion for fast titration: drift < 30 µL/min

Sample size:
2 mL

Procedure:
The titration medium is first placed into the cell and titrated dry by means of the titrant. Then the sample is added with a syringe (exact sample weight determination by weighing of syringe before and after injection) or volumetric pipette and the titration is started. Titration is carried out to fast end point. The KF solvent should be changed after each analysis.

Materials