Quality Control of Isocyanates

Importance of the Topic

Accurate determination of isocyanate content is critical in industrial quality control due to the high reactivity and toxicity of these compounds. Traditional wet‐chemical methods such as HPLC and titration involve time‐consuming sample preparation and use of reagents. A fast, chemical‐free alternative enhances laboratory throughput, reduces hazardous waste, and supports real‐time decision making in production environments.

Study Objectives and Overview

This application note evaluates the use of visible-near infrared spectroscopy (Vis-NIR) with the XDS RapidLiquid Analyzer for rapid, reagent-free quantification of isocyanates. The goal is to compare prediction performance and analysis speed against standard HPLC protocols outlined in ASTM D7252.

Methodology and Instrumentation

Samples of liquid isocyanate formulations were measured in transmission mode over 400–2500 nm at a controlled temperature of 30 °C. No chemical pretreatment was required. Spectral data acquisition and model development were performed using Vision Air Complete software.

• Measurement configuration: 8 mm disposable glass vials, path length 8 mm.
• Spectral range: 400–2500 nm, transmission mode.
• Temperature control: 30 °C built-in thermostat.
• Software: Vision Air Complete for data capture and multivariate calibration.

Main Results and Discussion

Multivariate calibration models relating Vis-NIR spectra to reference titration values achieved high accuracy and precision. Key figures of merit for the quantification of NCO content were:

• Coefficient of determination (R²): 0.968
• Standard error of calibration (SEC): 0.24 % NCO
• Standard error of cross-validation (SECV): 0.26 % NCO

These metrics indicate strong agreement between Vis-NIR predictions and primary wet-chemical results, with minimal bias and high reproducibility.

Benefits and Practical Applications

Vis-NIR spectroscopy offers several practical advantages over conventional methods:

• Analysis time under one minute versus up to 40 minutes for HPLC with sample prep.
• Elimination of reagents and disposal costs.
• Simple workflow requiring only vial loading and instrument start.
• Potential for high-throughput screening in production QC.

Used Instrumentation

The study employed the following Metrohm equipment and software:

• XDS RapidLiquid Analyzer (Cat. No. 2.921.1410)
• Disposable glass vials, 8 mm diameter (Cat. No. 6.7402.000)
• Vision Air 2.0 Complete spectroscopy software (Cat. No. 6.6072.208)

Future Trends and Opportunities

The demonstrated approach can be extended to inline process monitoring, integration with advanced machine learning algorithms, and miniaturized sensor platforms. Further development may target other reactive or hazardous analytes, enabling real-time PAT (process analytical technology) implementations and automated quality assurance.

Conclusion

Vis-NIR spectroscopy using the XDS RapidLiquid Analyzer provides a rapid, accurate, and chemical-free method for isocyanate quantification. With excellent calibration performance and analysis times below one minute, this technique represents a viable alternative to traditional HPLC and titration methods for routine QC.

References

• ASTM D7252: Standard Test Method for Determination of Isocyanate Content in Polyurethane Raw Materials by High Performance Liquid Chromatography
• Metrohm Application Note AN-NIR-068: Quality Control of Isocyanates