Determination of Water Content in Dimethylsulfoxide Using Karl Fischer Titration

Product Group

Sulphurous compounds, org.

General Information concerning the product group

Sulphurous compounds, org.

The majority of organic sulphuric compounds do not pose any problems to the water determination by Karl Fischer. The titration of e.g. organic sulphides and disulphides can thus be carried out following standard methods. During titration of sulphonic acids it should be noted that these can shift the pH of the KF solution into the acidic range, thus rendering further buffering of the system through the addition of a base (e.g. Aquastar^® buffer solution for strong acids, imidazole or 1-methyl imidazole) necessary. Disturbing side reactions occur during determination of thiophenes or mercaptans. Thio-compounds are oxidised by iodine and so mimic a water concentration that is too high. With such substances only the volumetric method can be employed.

Special Information concerning the sample and the methods

With dimethylsulfoxide a slow side reaction is observed in Karl Fischer solvents leading to poor results. The reason for this is the reduction of dimethylsulfoxide through iodine to the toxic dimethylsulphide. The iodine thus released reacts again in the KF solvent. Due to this side reaction only small sample sizes can be analysed before it is necessary to change the KF solvent. The coulometric method should not be applied.

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 188009 Aquastar^® - CombiMethanol - Solvent for volumetric Karl Fischer titration with one component reagents, max. 0.01 % water

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:
5 mL

Procedure:
The titration medium is first placed into the titration 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. After two to three analyses (concentration of dimethylsulfoxide in cell solution of max. 20 %) the KF solvent must be changed.

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

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:
5 mL

Procedure:
The titration medium is first placed into the titration 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. After two to three analyses (concentration of dimethylsulfoxide in cell solution of max. 20 %) the KF solvent must be changed.