Most often, the presence of water in pharmaceutical substances, petroleum products, or foodstuffs is unwanted. For example, if water content is too high, it can reduce the shelf life of grains like rice, cause issues with pharmaceutical products’ processability, or adversely impact the quality of plastic products.
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It is important that the water content of different materials is accurately determined to ensure quality control and optimized production processes.
Chemical methods suitable for determining water content often involve a chemical reaction between water and an appropriate reagent.
Measuring the amount of reagent consumed during the reaction enables the determination of the amount of water converted. Karl Fischer (KF) titration is the most widely recognized method using this principle, and the quantitative analysis technique offers several major advantages, including:
- High selectivity toward water
- A wide measuring range
- Rapid analysis capabilities
- Accuracy
- Repeatability
- Directness, with no additional reference method required.
Mettler Toledo offers a comprehensive portfolio of water content determination solutions using Karl Fischer titration, including a range of autosamplers and dedicated accessories designed for the unattended analysis of a high number of samples.
This new resource from Mettler Toledo explores the most important considerations when performing a Karl Fischer titration, covering intermediate and advanced topics.
The following guide features a brief overview of the method before focusing on three key areas:
Considerations for a Successful KF Titration
Achieving accurate and correct results via KF titration requires users to comprehensively understand the specific goals of the water content determination method performed. These four questions will support and guide users as they begin this process.
Sample Preparation
According to Karl Fischer, water content can only be determined successfully if water is freely available to undergo the chemical reaction. If water is not freely available, dedicated sample preparation is necessary to release water molecules from the sample matrix.
Frequently Asked Questions
A range of the most relevant frequently asked questions is included, making the document particularly valuable for users working with this technique.
Karl Fischer (KF) Titration
Titration is a simple, straightforward, and cost-effective technique suitable for determining the content of a specific analyte in sample solutions. Karl Fischer titration is the method of choice if the analyte is water.
This method determines water content by adding a known concentration of iodine (I2) to a sample dissolved in an alcoholic solution like methanol. Iodine reacts with water in a 1:1 ratio in a two-step reaction involving methanol, an organic base, and sulfur dioxide (SO2).
The German chemist Karl Fischer developed this analytical technique for the determination of the water content in petroleum products, resulting in this chemical reaction being referred to as a Karl Fischer (KF) reaction.
A double-pin platinum sensor measures the current in µA flowing between the two pins during titrant addition. The pins are polarized at a constant potential (Upol).
The titrant containing iodine is added until a predefined current endpoint is reached, for example, until a current of, e.g., 30 µA is reached (Figure 1). Volumetric KF titration sees titrant consumption up to this point measured in mL, enabling calculation of the water content in the sample.
In contrast, coulometric KF titration sees the iodine required for the KF reaction generated directly in the titration vessel via electrochemical processes.
Acknowledgments
Produced from materials originally authored by Mettler Toledo.
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