Determination of Water Content in 3-Mercaptopropane-1,2-diol 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

Various possibilities exist for the determination of water content of thio-compounds: - In mixtures that contain low concentrations of a thio-compound (e.g. petroleum products) the side reaction can be frozen through cooling of the titration cell. With less than 10 ppm the disturbing influence is negligible. - For known concentrations an arithmetic consideration of the side reaction is possible, as long as it occurs quickly and completely. Then 1 mol -SH corresponds to 0.5 mol water - The simulated water concentration can be determined through iodometric titration and then subtracted from the result of the KF titration - the apparent water content. - The transformation of the thio-compound with an unsaturated compound (octene or n-ethyl maleic imide) and subsequent KF titration, however, are preferred. The addition of imidazole ensures further buffering of the system.

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
and
2 g / 1 - 2 g 104716 / 101308 Imidazole / n-ethyl maleic imide - null

Titration Parameters:
Stirring time: 5 min.
Default titration settings, e.g.:
I(pol) = 20 - 50 µA, U(EP) = 100 - 250 mV
Stop criterion: drift < 20 µL/min

Sample size:
0.5 - 1 mL

Procedure:
The titration medium is first placed into the titration cell together with the imidazole and the n-ethyl maleic imide and titrated dry by means of the titrant. Then the sample is added with a 1 mL syringe (exact determination through weighing of syringe before and after injection) . After a stirring time of five minutes titration is started.

Materials

     
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