Laboratory Products

Speed up your Karl Fischer titration with HYDRANAL-Methanol Rapid

Nov 01 2017 Read 453 Times

Karl Fischer (KF) titration is a fast and accurate method for the determination of water content in all types of substances, including pharmaceuticals, chemicals, oils, and food. In 1979, researcher Dr. Eugen Scholz improved Karl Fischer titration by replacing noxious pyridine with imidazole. This innovation became the foundation of Hydranal™, the world’s leading pyridine-free reagents for Karl Fischer titration. The use of imidazole instead of pyridine is greatly improving the speed of the KF reaction.

When using these modern reagents, the speed, time and accuracy of the Karl Fischer reaction is influenced by the medium used in the titration vessel. For volumetric KF titration the most often used reagent combination is a one-component reagent titer 5 with dry methanol. One-component reagents contain all the substrates for KF reaction dissolved in a suitable alcohol. In Hydranal-Composite, one-component reagent, all the reactants including iodine, sulfur dioxide, and the bases imidazole and 2-methylimidazole, are dissolved in diethylene glycol monoethyl ether (DEGEE). Adding 2-methylimidazole in addition to imidazole improves the stability and eliminates the formation of crystals which can interfere with the titrator’s performance. DEGEE used as a solvent additionally stabilizes the reagent. The speed of KF reaction depends on the pH value. The time needed to reach the end-point of the titration will depend on the buffering system used in the reagent. The Hydranal-Composite reagents are already buffered to an optimum pH by using imidazoles. Thus the performance of the titrating agent is optimized to ensure a rapid Karl Fischer reaction, however, there is still room for improvement on the use of the solvent.

Dry methanol is the most commonly used medium in the titration vessel, however it is an unbuffered solvent. Hydranal-Methanol Rapid contains accelerators for the KF reaction and reduces titration times significantly. The volume of Hydranal-Composite dosed into the titration vessel during conditioning depends on the water content of the methanol. Even if a titration vessel is in a good condition, the pre-titration of the methanol usually takes between 1 to 2 minutes. The following titration of an average amount of water in the samples takes 3 to 4 minutes. When using Hydranal Methanol Rapid, you will see a clear improvement in speed and accuracy of the titration. This is due to the accelerators in the medium, which are unique to Hydranal-Methanol Rapid and enable an optimal Karl Fischer titration.

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