Determination of Water Content in Sodium tert-butoxide 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

Like all other alkaline alcoholates sodium tert-butoxide immediately reacts with water to form sodium hydroxide. Thus there is no free water here. In the Karl Fischer solution sodium hydroxide is neutralised again under the formation of water. Hence by means of KF titration it is possible to deduce the concentration of NaOH. For complete neutralisation of the substance salicylic acid is added to the solvent. Due to its better buffering properties the two component titration is preferred. The hygroscopic properties of some alcoholates should be noted and samples accordingly handled with care.

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
and
10 g 100635 salicylic acid - as buffer substance

Titration Parameters:
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
1 g

Procedure:
The titration medium is first placed into the cell together with the salicylic acid 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 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
10 g 100635 salicylic acid - as buffer substance

Titration Parameters:
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
1 g

Procedure:
The titration medium is first placed into the cell together with the salicylic acid 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.