Water content in carbon dioxide using Karl Fischer titration

Importance of the topic

Accurate determination of trace water in carbon dioxide is crucial for maintaining product quality and process safety in industries such as food packaging, semiconductor manufacturing and pharmaceuticals. Karl Fischer titration offers high sensitivity and selectivity for water analysis in nonaqueous gas matrices.

Objectives and Study Overview

This study aims to automate the measurement of water content in CO2 using a modified Metrohm 875 KF Gas Analyzer. The method was developed to improve throughput and precision while handling low water levels in compressed gas samples.

Methodology and Instrumentation Used

Sample Preparation:

• Liquid-phase CO2 drawn from a pressurized cylinder
• Connection via PEEK capillary (0.5 mm i.d.) for calibration and measurement

Reagents:

• HYDRANAL-Coulomat AG-oven
• HYDRANAL-Coulomat CG
• Dry nitrogen (5.0, <3 ppm H2O)

Instrument Modification and System Setup:

• Replacement of control valve with 30 cm PEEK capillary (0.18 mm i.d.) to regulate CO2 flow
• System flushed with sample gas then purged with nitrogen to minimize start drift

Used Instrumentation

• Metrohm 875 KF Gas Analyzer (model 2.875.9020)
• PEEK capillaries: 30 cm × 0.18 mm (6.183.1130), 40 cm × 0.5 mm (6.183.1050)
• Various Swagelok fittings

Main Results and Discussion

The automated method yielded an average water content of 99.0 ppm (n = 6) with a relative standard deviation of 0.38 %. The low drift and high repeatability demonstrate the robustness of the modified setup. Professional installation of the modification is recommended to ensure system integrity.

Benefits and Practical Applications

Automation of CO2 water analysis reduces operator influence and increases sample throughput. The method provides precise, reliable data for quality control and compliance in industrial gas production.

Future Trends and Opportunities

Emerging trends include inline moisture monitoring for continuous process control, miniaturized titration cells for field use, and adaptation of the approach for other industrial gases.

Conclusion

The modified Karl Fischer titration method on the 875 KF Gas Analyzer delivers accurate, reproducible measurement of water in CO2. Its automation and low detection limits make it suitable for routine quality assurance in various industries.