Determination of Water Content in Paraffin Using Karl Fischer Titration

Product Group

Hydrocarbons

General Information concerning the product group

Hydrocarbons

Saturated hydrocarbons can in most cases be titrated according to standard methods. To overcome solubility problems of unpolar or weakly polar substances, the addition of a solubiliser to the solvent is necessary. In the case of long-chain and cyclic hydrocarbons, long-chain alcohols (e.g. propyl alcohol or decyl alcohol) or chloroform are thus recommended. Toluene, xylene or chloroform improve the solubility of aromatic compounds. Unsaturated hydrocarbons can usually be titrated in the same way. Interferences due to double bonds only occur with some very reactive compounds. In the case of interferences (unstable end point or none at all) a methanol-free, alcoholic solvent (e.g. CombiSolvent or CombiSolvent Keto) should be utilised instead of methanol. Recommended methods are both the volumetric titration with one or two component reagents, as well as the coulometric analysis. The latter is predominantly applied for low water concentrations (< 0.1 %).

Special Information concerning the sample and the methods

This substance is hardly soluble in methanol. For water determination by Karl Fischer the addition of a solubiliser to the KF solvent is necessary.

Titration one component system

Reagents:

Titrant
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
or
30 mL / 20 mL 188009 / 102445 Aquastar™ - CombiMethanol / Chloroform - solvent mixture for one component titration

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:
5 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 syringe without needle (exact sample weight determination through weighing of syringe before and after injection) or volumetric pipette 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
188011 Aquastar™ - Titrant 2 - Titrant for volumetric titration with two component reagents, 1 mL = approx. 2 mg water

Solvent
30 mL 188015 Aquastar™ - Solvent - Solvent for volumetric titration with two component reagents
and
20 mL 102445 Chloroform - 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:
5 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 syringe without needle (exact sample weight determination by weighing of syringe before and after injection) or volumetric pipette and the titration is started. For complete dissolution of the sample a stirring time of 60 seconds is recommended.

Coulometry with diaphragm

Reagents:

Catholyte
5 mL 109255 Aquastar™ - CombiCoulomat frit - Coulometric Karl Fischer reagent for cells with diaphragm

Anolyte
80 mL 109255 Aquastar™ - CombiCoulomat frit - Coulometric Karl Fischer reagent for cells with diaphragm
and
40 mL 102445 Chloroform - as solubiliser (alternatively xylene)

Titration Parameters:
Stirring time: 60 sec.
Default coulometer settings for cell with diaphragm:
For end point indication, e.g.:
I(pol) = 5 - 10 µA, U(EP) = 50 - 100 mV
Stop criterion: drift < 10 µg/min

Sample size:
1 mL

Procedure:
The Karl-Fischer reagent is placed into the cathode and anode compartment of the titration cell with diaphragm. The coulometer is started and the solvent is titrated dry. After preliminary titration and stabilisation of drift the sample is injected into the titration cell with a syringe (exact sample weight determination by weighing of syringe before and after injection) and the water determination is started. For complete dissolution of the sample a stirring time of 60 seconds is recommended.

Coulometry without diaphragm

Reagents:

Working medium
80 mL 109257 Aquastar™ - CombiCoulomat fritless - Coulometric Karl Fischer reagent for cells with or without diaphragm
and
20 mL 102445 Chloroform - as solubiliser (alternatively xylene)

Titration Parameters:
Stirring time: 60 sec.
Default coulometer settings for cell without diaphragm:
For end point indication, e.g.:
I(pol) = 5 - 10 µA, U(EP) = 50 - 100 mV
Stop criterion: drift < 10 µg/min

Sample size:
1 mL

Procedure:
The Karl-Fischer reagent is placed into the titration cell without diaphragm. The coulometer is started and the solvent is titrated dry. After preliminary titration and stabilisation of drift the sample is injected into the titration cell with a syringe (exact sample weight determination by weighing of syringe before and after injection) and the water determination is started. For complete dissolution of the sample a stirring time of 60 seconds is recommended.

Materials

     
Related Links