Determination of Water Content in Hydroquinone monomethyl ether Using Karl Fischer Titration

Product Group

Ethers, Phenols

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.

Phenols

In most phenols water determination can be carried out according to the standard methods after Karl Fischer. Some substances, however, are oxidised by the Karl Fischer reagent. This side reaction leads to unstable or dragging end points. During coulometry, interferences can accumulate to the point where analysis becomes impossible. Because the side reaction is dependent on the pH, its influence can be reduced through modification of the solvent. In a weakly acidic titration environment (e.g. through the addition of Aquastar™ buffer solution for strong bases, benzoic or salicylic acid) easily oxidisable substances can be determined nevertheless.

Special Information concerning the sample and the methods

Due to an interfering side reaction with iodine only the volumetric titration method with one component reagents is recommended. This substance is easily soluble in alcoholic media.

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 188008 Aquastar™ - CombiSolvent - Methanol-free solvent for volumetric Karl Fischer titration with one component reagents
or
50 mL 188009 Aquastar™ - CombiMethanol - Solvent for volumetric Karl Fischer titration with one component reagents, max. 0.01 % water

Titration Parameters:
Stirring time: 60 - 120 sec.
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 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 to 120 seconds is recommended. Titration is carried out to fast end point.

Materials

     
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