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A detailed guide offers specific advice on Karl Fischer (KF) titration analysis as part of the METTLER TOLEDO Good Titration Practice™ (GTP) program.
KF titration is an accurate method for water determination at levels from a few ppm to near saturation. As technique optimization for different sample types may pose challenges, we present extensive background information and recommendations on:
- Chemistry and control of the Karl Fischer titration
- Practical sample preparation and instrument operation
- Ways to optimize the accuracy and precision of the water determination
- Selecting the optimal method for water determination of your specific sample
- Troubleshooting unexpected results
Water determination with Karl Fischer titration
Principle:
Karl Fischer titration is used for many substances as a reference method, and is a chemical analysis based on the oxidation of sulfur dioxide by iodine in a methanolic hydroxide solution. In principle, the following chemical reaction takes place:
H2O + I2 + SO2 + CH3OH + 3RN -> [RNH]SO4CH3 + 2[RNH]I
The titration can be performed volumetrically or coulometrically.
In the volumetric method a Karl Fischer solution containing iodine is added until the first trace of excess iodine is present. The amount of iodine converted is determined from the burette volume of the iodine-containing Karl Fischer solution.
In the coulometric procedure, the iodine participating in the reaction is generated directly in the titration cell by electrochemical oxidation of iodide until again a trace of unreacted iodine is detected. Faraday's law can be used to calculate the amount of iodine generated from the quantity of electricity required.
Application:
The Karl Fischer titration is a moisture determination method specific for water and is suitable for samples with a high water content (titrimetry) and also for those with water content in the ppm range (coulometry). It was originally developed for nonaqueous liquids, but is also suitable for solids if these are soluble or if the water they contain can be removed by heating in a stream of gas or by extraction.
Advantages:
Accurate reference method, coulometry also suitable for trace analysis and water detection.
Restriction:
The working method must be adapted to the specific sample.
