C. Lim | IKA Product Manager; Mettler Toledo

Volumetric Karl Fischer Water Determination using an IKA homogenizer

Image credits: Mettler Toledo

Determining water content in difficult-to-process samples using volumetric Karl Fischer (KF) titration is a complex analytical challenge. While KF titration is the gold standard for water determination in solids, liquids, and gases, certain sample matrices like creams, powders, and solids can complicate the process. The IKA T 25 easy clean digital homogenizers of the ULTRA-TURRAX® family offer a game-changing solution by simplifying sample preparation and accelerating analysis.

This article explores how our high-speed homogenizer works in tandem with the METTLER TOLEDO EVA V1 AND V3 KF titrator to achieve precise and efficient results for a range of sample types, including milk powder, moisturizer, almonds, and gummy candies.

The role of the homogenizer in Karl Fischer titration

Volumetric KF titration relies on the reaction between water, iodine, sulfur dioxide, an amine base, and a short-chain alcohol to determine water content. For liquids and gases, extracting water into the KF solvent is straightforward. However, solids and semi-solid samples, such as powders, gels, and oily matrices, pose significant challenges due to poor solubility in KF solvents.

The IKA T 25 easy clean and T 25 mini control homogenizers mitigate these challenges by:

Efficiently dispersing powders.
Shredding solids into finer particles to release water trapped within the matrix.
Reducing analysis time by integrating sample preparation directly into the titration process.

Process automation
The new generation of the IKA T 25 easy clean and T 25 mini control also offers the advantage of being able to connect and communicate with more automated titrators such as the new generation METTLER TOLEDO V3 KF titrators. The disperser can be seamlessly integrated into the titration workflow and starts crushing the sample automatically before the water measurement.

Testing four challenging samples

1. Milk Powder
Milk powder, which resists dissolution in KF solvents, was dispersed effectively using the homogenizer. This facilitated faster water extraction, streamlining the analysis process.
Preparation: Direct addition to the KF cell; weight determined using the back-weighing technique.

2. Moisturizer Cream
Moisturizer cream contains oil-based components that complicate water determination. The homogenizer dispersed the cream uniformly, ensuring reliable results.
Preparation: Pre-filled into syringes for accurate dosing (0.02–0.04 g) and back-weighing.

3. Almonds
Solid almonds require shredding into smaller pieces to release water effectively. The homogenizer converted these fragments into a thick slurry suitable for KF analysis.
Preparation: Pre-cut almonds into 3–4 mm pieces using a knife or blender before homogenization.

4. Gummy Candies
Gelatin-based gummy candies dissolve slowly in KF solvents. The homogenizer, combined with the co-solvent formamide, significantly reduced dissolution time.
Preparation: Cut into ~5 mm pieces before homogenization in a 3:1 methanol-formamide solvent.

Key Steps for Titration

Blank Determination: Ensure accurate compensation for moisture introduced by the homogenizer.
Sample Homogenization: Operate the homogenizer at speeds up to 25,000 rpm for uniform dispersion.
Titration: Use a suitable KF titrant and solvent that facilitates the dissolution of the sample.

Results and Observations

Repeatability: Highly consistent results were achieved for most samples.

Gummy candies showed the highest repeatability with a relative standard deviation (RSD) <0.6%.
Almonds, as the most challenging matrix, yielded an RSD of 4.6%, within acceptable limits for non-dissolvable samples.

Efficiency: The homogenizer reduced preparation and analysis time, especially for complex matrices like gummy candies.

Practical Insights

Blank Variability: Variations in blank measurements can stem from splashing during homogenization or environmental moisture. Regular system checks and adjustments are recommended.
Optimized Parameters: Homogenizer speed and duration can be tailored for specific sample matrices to ensure optimal results.

Safety and Disposal

Handling KF reagents requires appropriate safety measures:

Personal Protective Equipment (PPE): Always wear gloves, safety goggles, and a lab coat.
Waste Disposal: Dispose of KF waste as organic solvent waste following local regulations.

Conclusion

The IKA T 25 easy clean digital and T 25 mini control homogenizers enhances the efficiency and accuracy of volumetric Karl Fischer titration for challenging samples. By integrating sample preparation directly into the analysis process, this robust solution significantly simplifies workflows and minimizes manual effort.