Quantification and Chemical Identification of NOx Reduction Agent AdBlue (AUS32) Using ATR-FTIR

Importance of the Topic

The control of NOx emissions in diesel engines is critical for environmental compliance and public health. AdBlue, a high-purity aqueous urea solution, must meet strict ISO 22241 specifications to ensure efficient SCR performance. Rapid and reliable methods for verifying AdBlue quality and urea concentration support regulatory adherence and operational efficiency in automotive and industrial settings.

Objectives and Study Overview

This application note explores the use of ATR-FTIR spectroscopy on an Agilent Cary 630 FTIR to identify and quantify urea in commercial AdBlue. The specific goals are:

• Create a fast qualitative method for AdBlue identification according to ISO 22241-2 Annex J.
• Develop a linear calibration model for routine urea quantification in AdBlue using Agilent MicroLab Quant software.
• Validate the method against standard ISO combustion and refractive index techniques for accuracy and precision.

Methodology and Instrumentation

Samples of commercial AdBlue and a 32.5% w/w urea standard were prepared. ATR-FTIR spectra were collected on the Cary 630 FTIR with diamond single reflection module. Key parameters included spectral range 4000–650 cm–1, 256 scans per sample, and 4 cm–1 resolution. The MicroLab software guided the user through identification and quantification workflows via intuitive pictures and automated parameter settings.

Main Results and Discussion

Identification

• Commercial and reference AdBlue samples yielded high Hit Quality Indices (HQI 0.998 and 0.999), clearly distinguishing them from water (HQI 0.824).

Quantification

• A linear calibration curve based on the urea peak at 1157 cm–1 achieved R = 0.99934.
• Cross-validation and independent set validation with control samples (6–43% w/w urea) gave total standard errors below 0.2%.
• Repeatability tests on six replicates of a 32.5% w/w standard returned precision of 0.3% RSD and accuracy above 99%.

Benefits and Practical Applications

The FTIR-based method offers:

• Non-destructive, reagent-free analysis with minimal sample preparation.
• Rapid analysis time of ~2.5 minutes per sample (can be reduced further).
• Automated workflows and color-coded results to minimize operator error.

Future Trends and Potential Applications

Integration of ATR-FTIR into on-site monitoring and inline process control may improve real-time quality assurance. Advances in chemometric methods and portable FTIR designs could extend this approach to other urea-based formulations and environmental monitoring applications.

Conclusion

The Agilent Cary 630 FTIR with ATR sampling and MicroLab software provides a robust, economical, and user-friendly alternative to ISO 22241-2 compliance methods for AdBlue quality control, delivering high accuracy, precision, and throughput.

Used Instrumentation

The Cary 630 FTIR spectrometer equipped with a single reflection diamond ATR module and Agilent MicroLab software version 5.7 was employed.

References

1. Foerter, D. C.; Whiteman, C. S. Typical Installation Timelines for NOx Emissions Control Technologies on Industrial Sources; Institute of Clean Air Companies, 2006.
2. Fojtikova, P.; et al. Tracking AdBlue Properties During Tests of Selective Catalytic Reduction (SCR) Systems: Suitability of Analytical Methods for Urea Content Determination. Int. J. Energy Res. 2020, 44, 2549–2559.