Determination of Water Content in Polyethylene Glycol 1000 Using Karl Fischer Titration
Product Group
Alcohols
General Information Concerning the Product Group
Alcohols
Water determination after Karl Fischer poses no problems for most alcohols. Alcohols are easily soluble in the common Karl Fischer working media. Only alcohols with very long chains require the addition of solubilisers. Side reactions are not to be expected. Suitable methods are both the volumetric titration with one or two component reagents as well as the coulometric determination. The latter method is predominantly applied for low water concentrations (< 0.1%).
Special Information Concerning the Sample and the Methods
Polyethylene glycol 1000 is not quite as easily soluble in methanol. Therefore, the addition of a solubiliser (e.g. chloroform) is necessary. For one component titration CombiSolvent oils is well suitable as solvent. Coulometric analysis is possible, but not necessarily recommended.
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
or
30 mL / 20 mL 188009 / 102445 Aquastar® - CombiMethanol / Chloroform - solubiliser mixture for one component titration
Titration Parameters:
Stirring time: 3 min.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min
Sample size:
5 g
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 dissolution of the sample a stirring time of 3 minutes 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 188015 Aquastar® - Solvent - Solvent for volumetric titration with two component reagents
and
20 mL 102445 Chloroform - as solubiliser
Titration Parameters:
Stirring time: 3 min.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min
Sample size:
5 g
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 dissolution of the sample a stirring time of 3 minutes 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
20 mL 102445 Chloroform - as solubiliser
Titration Parameters:
Stirring time: 120 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:
0.5 g
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 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 dissolution of the sample a stirring time of 120 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
Titration Parameters:
Stirring time: 120 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:
0.5 g
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 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 dissolution of the sample a stirring time of 120 seconds is recommended.