Metrohm 907 Titrando - Manual (Page 42)

4.1 Volumetric titration
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907 Titrando
4.1.3 Karl Fischer reagents
One-component reagents
They contain all the reactive parts in a single solution – iodine, sulfur diox-
ide and a base, dissolved in an appropriate alcohol.
Two-component reagents
The reactive parts are distributed among two separated solutions. The
titration reagent contains iodine in methanol. The KF solvent is a solution
of sulfur dioxide and a base in methanol. It is used as a working medium
in the KF titration cell.
4.1.4 Application of the Karl Fischer titration
The volumetric Karl Fischer titration is the method of choice for determin-
ing quantities of water between 0.1 and 100%. It has the advantage that
even solid and pasty samples can be added directly to the titration vessel.
In addition, various organic solvents can be used that are tailored to the
respective samples.
4.1.5 Working with water standards
4.1.5.1 Certified water standards
Commercially available, certified water standards with a water content of
10.0 ± 0.1 mg/g should be used for validating the instrument as a whole,
integrated system.
4.1.5.2 Practical recommendations
For validation, it is essential to work very accurately. In order to minimize
any measurement inaccuracies that could occur, the sample preparation
and the sample processing should proceed in accordance with a defined
scheme:
1 Put on gloves (always with Karl Fischer titration).
2 Use a clean syringe.
3 Take a new ampoule of water standard and shake it briefly.
4 With a folded paper towel held between thumb and index finger,
break open the ampoule at the marking.
5 Draw approx. 1 mL of the water standard into the syringe.