Automated water content determination with the 874 Oven Sample Processor

Significance of the Topic

Precise water content determination is vital in diverse industries such as food, pharmaceuticals, plastics and petrochemicals. Moisture levels influence product stability, shelf life, performance and regulatory compliance. Automated methods reduce operator error and increase sample throughput while maintaining trace-level sensitivity.

Objectives and Study Overview

This application bulletin demonstrates how the 874 Oven Sample Processor combined with coulometric Karl Fischer titration automates water determination. The oven technique enables analysis of samples that are incompatible with direct titration, for instance those containing interfering substances or difficult sample matrices. Examples cover food additives, pharmaceutical dosage forms, polymers, oils and petrochemical products.

Methodology and Instrumentation

The core setup comprises:

• 874 Oven Sample Processor for controlled heating and gas extraction
• Coulometric KF titrator with double platinum wire and generator electrodes (with option for diaphragm)
• Special oven-compatible KF reagents
• Carrier gas (nitrogen preferred) dried over molecular sieves
• Sealed sample vials with septum caps and inert needles for gas delivery

Workflow steps:

1. System preparation and conditioning of titration cell to remove residual moisture
2. Blank determination using empty vials to establish baseline drift
3. Sample heating under a defined temperature program or constant oven temperature, driving moisture into the carrier gas stream
4. Transport of released water into the titration cell for coulometric KF endpoint detection
5. Calculation of absolute water content by correcting for blank and drift

Temperature gradients (2 °C/min and slower ramps) guide optimal selection of oven setpoint, ensuring complete release of bound water without decomposing the sample. Software (tiamo) controls sequences, records drift profiles and correlates water release kinetics with temperature.

Main Results and Discussion

Temperature-ramp experiments on sodium tartrate dihydrate revealed distinct stages of surface and crystal water release from 50 to 140 °C. A drift increase above 190 °C indicated onset of sample decomposition. Based on these data, an oven temperature of 160 °C was chosen for routine analysis. Application data showed reliable moisture determination in over 30 sample types, with detection limits down to single µg per gram and relative standard deviations typically below 1%.

Benefits and Practical Applications

The combined oven extraction and coulometric KF method offers:

• Fully automated operation with minimal operator intervention
• Trace level sensitivity for low-moisture samples
• Wide applicability to solids, liquids, powders and viscous materials
• Short cycle times with adjustable gas flow and temperature profiles
• Integrated drift correction and quality checks via software

This workflow supports routine QA/QC in food processing, pharmaceutical manufacturing, polymer quality control and petrochemical analysis.

Future Trends and Potential Uses

Emerging developments include integration of real-time feedback loops, machine learning for predictive drift correction, miniaturized oven modules for smaller sample volumes and coupling with automated sample preparation robots. Applications may expand into battery electrode analysis, advanced composites and high-throughput screening of porous materials.

Conclusion

The oven technique paired with coulometric Karl Fischer titration provides a robust, versatile and sensitive solution for routine moisture analysis. Its automation and adaptability to challenging matrices make it a valuable tool for modern analytical laboratories.

Reference

• Metrohm Monograph 8.026.5013 - Water Determination by Karl Fischer Titration
• AN-K-048 - Sample Preparation with the Oven Technique – Relative Blank, Metrohm