Determination of Water Content in Pyrocatechol, 1,2-Dihydroxybenzene Using Karl Fischer Titration

Product Group

Alcohols, Phenols

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%).

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 the disturbing side reactions with the Karl Fischer reagent, only the volumetric method is used. 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™ - Combi Titrant 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: 1 -2 min
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:
3 - 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. Titration is carried out to fast end point. For complete dissolution of the sample a stirring time of 1 - 2 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
50 mL 188015 Aquastar™ - Solvent - Solvent for volumetric titration with two component reagents
and
5 g 100635 Salicylic acid - as buffer substance

Titration Parameters:
stirring time: 1 - 2 min
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:
3 - 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 with a syringe (exact sample weight determination by weighing of syringe before and after injection) or volumetric pipette and the titration is started. Titration is carried out to fast end point. For complete dissolution of the sample a stirring time of 1 - 2 minutes is recommended.

Materials

     
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