Determination of Water Content in Trioxane Using Karl Fischer Titration

Product Group

Ethers

General Information concerning the product group

Ethers

In most cases ethers can be determined after Karl Fischer standard methods analogously to hydrocarbons. Long-chain compounds require the addition of solubilisers, e.g. long-chain alcohols or chloroform. 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 %). One exception are the vinyl ethers, which cause an interfering side reaction with methanolic Karl Fischer reagents.

Special Information concerning the sample and the methods

For acceleration of solubility a solubiliser (e.g. long-chained alcohols or chloroform) is added to the methanolic KF solvent. Alternatively, special KF solvents for less polar substances may be utilised.

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 188021 Aquastar™ - CombiSolvent fats - Solvent for volumetric Karl Fischer titration with one component reagents for fats
or
30 mL / 20 mL 188009 / 803463 Aquastar™ - CombiMethanol / Decanol - solvent mixture for one component titration

Titration Parameters:
Stirring time: 60 - 120 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 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 60 - 120 sec 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
50 mL 188016 Aquastar™ - Solvent oils & fats - Solvent for volumetric Karl Fischer titration with two component reagents for oils & fats

Titration Parameters:
Stirring time: 60 - 120 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 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 60 - 120 sec 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 803463 Decanol - null

Titration Parameters:
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:
0.3 g

Procedure:
The Karl-Fischer reagent is placed into the cathode and anode compartment of the titration cell with diaphragm. After addition of the decanol, 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. Alternatively, the sample can be dissolved in an external solution. An aliquote of the solution is coulometrically analysed. The result must be corrected for the blank value of the solvent.

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 803463 Decanol - null

Titration Parameters:
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:
0.3 g

Procedure:
The Karl-Fischer reagent is placed together with the decanol into the titration cell without diaphragm. After addition of the decanol, 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. Alternatively, the sample can be dissolved in an external solution. An aliquote of the solution is coulometrically analysed. The result must be corrected for the blank value of the solvent.

Materials

     
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