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

Importance of the topic

Commercial diesel vehicles equipped with selective catalytic reduction (SCR) systems rely on high-purity urea solutions (AdBlue) to reduce harmful NOx emissions. Compliance with ISO 22241 standards is essential to ensure product quality and environmental protection. Rapid and reliable analytical methods are critical for quality control and regulatory verification of urea concentration in AdBlue.

Objectives and study overview

This application note demonstrates the use of an Agilent Cary 630 FTIR spectrometer, equipped with a diamond ATR module, to perform both qualitative identification and quantitative determination of urea content in commercial AdBlue. The goal is to establish a simpler, faster, and more economical alternative to the ISO 22241-2 combustion and refractive index methods.

Methodology and instrumentation

Analyses were conducted on an Agilent Cary 630 FTIR with a single-reflection diamond ATR sampling module. Key experimental parameters included a spectral range of 4000–650 cm–1, a resolution of 4 cm–1, and 256 co-added scans per measurement. The Agilent MicroLab software guided users through a library-based qualitative method (HQI scoring) and a quantitative workflow using MicroLab Quant. Calibration standards ranged from 10 to 60% w/w urea, and control samples at 6, 12, 29, 33, and 43% w/w were used for validation.

Key findings and discussion

Qualitative identification achieved high Hit Quality Index (HQI) values (>0.998) for standard and commercial AdBlue samples, with clear differentiation from water. Quantitative calibration yielded excellent linearity (R=0.99934) based on the area of the characteristic urea peak (~1157 cm–1). Cross-validation and independent set validation showed total standard errors of 0.18% and 0.19%, respectively. Repeatability studies on six portions of a 32.5% w/w urea standard produced a relative standard deviation of 0.3% and accuracy >99%.

Benefits and practical applications

FTIR-ATR provides minimal sample preparation, no consumables, and rapid results (~2.5 minutes per sample). The method reduces operator error through guided software and color-coded outputs. It offers a cost-effective option for routine urea content verification in quality control laboratories, replacing more time-consuming ISO 22241-2 procedures.

Future trends and potential applications

Advancements may include automated sampling interfaces for high-throughput screening, integration with in-line process monitoring, and application of chemometric and machine learning algorithms for multi-component analysis. Miniaturization and portable FTIR systems could enable field testing of urea-based fluids and other industrial formulations.

Conclusion

The Agilent Cary 630 FTIR-ATR instrument combined with MicroLab software delivers a robust, accurate, and user-friendly solution for routine qualitative and quantitative analysis of AdBlue. It aligns with ISO 22241 requirements while offering significant savings in time, cost, and operational complexity.

References

• Foerter DC, Whiteman CS. Typical Installation Timelines for NOx Emissions Control Technologies on Industrial Sources. Institute of Clean Air Companies (ICAC), December 2006.
• Fojtikova P, et al. Tracking AdBlue Properties During Tests of Selective Catalytic Reduction (SCR) Systems ‐ the Suitability of Various Analytical Methods for Urea Content Determination. Int. J. Energy Res. 2020, 44, 2549–2559.