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Volumetric Karl Fischer Titration / Two-Component Reagents Available Online:
Titration Steps: Addition of HYDRANAL®-Titrant/Titrant E HYDRANAL®-Titrant / E is filled into the burette from the stock vessel for the burette. Stock vessel, valves and interconnections must be completely dry. The stock vessels are protected from atmospheric moisture by the addition of drying tubes. Addition of HYDRANAL®-Solvent/Solvent E 20-40 mL of HYDRANAL®-Solvent / E are added to the titration vessel. The amount added depends primarily on the size of the titration cell. The titration cell is sealed immediately following the addition of HYDRANAL®-Solvent / E in order to keep the unavoidable intrusion of atmospheric moisture to an absolute minimum. Pre-titration The HYDRANAL®-Solvent / E added to the titration vessel is titrated to dryness with HYDRANAL®-Titrant / E . This "pre-titration" removes not only the residual water that was in the solvent, but also the adherent moisture in the cell, on the walls of the cell and the electrode. The atmosphere of the cell is also dried of moisture. A particularly slow pretitration must be undertaken on account of the high reactivity of this reagent. The instrumentation used should be equipped with a particularly fast stirrer to ensure an efficient distribution within the cell. The stir rate should however be such that the inclusion of potential moisture from the cell atmosphere is prevented. Weighing the Sample The cell is opened for as short a time as necessary and then closed again immediately after the sample is added. In addition, it must be remembered that the HYDRANAL®- Solvent / E has a defined and limited capacity for water which cannot be exceeded. Usually, an effective water capacity of approximately 7 mg H2O/ml of HYDRANAL®-Solvent / E is anticipated, i.e. if 20 mL HYDRANAL®-Solvent / E are available, a water content of max. 140 mg H2O can be titrated. The titration of smaller samples presents no problem. 
Titration The titration of water is started immediately after the sample is added. The initial stages of the titration should be completed quickly. Reduce the titration rate when approaching the end point. A stable end point must be achieved otherwise the results of the titration are in doubt. Replacement of HYDRANAL®-Solvent/E Following completion of the titration, the spent working medium should be removed from the cell. Fresh HYDRANAL®-Solvent / E is then added and the pre-titration repeated. This ensures a prepared working medium for the next titration. Subsequent titrations are also possible using the two-component titration system. The water capacity of the solvent component must however be taken into consideration. If 20 mL HYDRANAL®-Solvent / E have been applied, a maximum of 28 mL of HYDRANAL®- Titrant / E can be consumed during the subsequent titrations. Otherwise the water content of the solvent component will be exceeded. |
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