Determination of Water Content in Tar Using Karl Fischer Titration

Product Group

Petroleum products

General Information concerning the product group

Petroleum products

Petroleum products are mixtures of long-chain or aromatic hydrocarbons. They are hardly soluble in methanol. Water determination by Karl Fischer therefore requires the addition of solubilisers. For light oils, long-chain alcohols are suitable. For dissolving of heavier oils toluene, xylene or chloroform are added. For the volumetric titration specific KF solvents for oils are available. Due to the very low water concentration titrants with a low factor (2 mg/ml or 1 mg/ml) are recommended. During coulometric determination without diaphragm 20% solubiliser can be added to the working medium, or 40% solubiliser to the anolyte in the case of coulometry with diaphragm. Note that oils are often heterogeneous compounds with uneven distribution of water and should thus be homogenised (e.g. with Ultra-Turrax) prior to KF determination. Additives in oils can cause side reactions during KF determination. Here, the direct coulometric analysis is not possible, the volumetric titration only conditionally. As an alternative, the KF oven technique can be utilised in combination with coulometry, whereby the release of water is best achieved at temperatures between 120 and 140 °C.

Special Information concerning the sample and the methods

Water determination of tar can only be carried out directly by means of the volumetric method. Toluene and chloroform are suitable solubilisers. Specific solvents for oils are available for one and two component titration. The tar sample should be well homogenised prior to analysis.

Titration one component system

Reagents:

Titrant
188005 Aquastar^® - CombiTitrant 5 - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 5 mg water
or
188002 Aquastar^® - CombiTitrant 2 - One component reagent for volumetric Karl Fischer titration, 1 mL = approx. 2 mg water

Solvent
50 mL 188020 Aquastar^® - CombiSolvent oils - Solvent for volumetric Karl Fischer titration with one component reagents for oils

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

Sample size:
0.5 - 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 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 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
or
188011 Aquastar^® - Titrant 2 - Titrant for volumetric titration with two component reagents, 1 mL = approx. 2 mg water

Solvent
30 mL 188016 Aquastar^® - Solvent oils & fats - Solvent for volumetric Karl Fischer titration with two component reagents for oils & fats
and
20 mL 108325 Toluene - as solubiliser

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

Sample size:
0.5 - 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 needle (exact sample weight determination by weighing of syringe before and after injection) and titration started. For complete dissolution of the sample a stirring time of 60 seconds is recommended.