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

Significance of the topic

AdBlue, a 32.5% w/w aqueous urea solution, is essential for reducing NOx emissions in diesel engines via selective catalytic reduction (SCR). Ensuring its identity, purity, and concentration is vital for regulatory compliance (ISO 22241) and for protecting air quality. Routine quality control demands fast, reliable, and cost-effective analytical methods.

Study objectives and overview

This application study evaluates the use of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) with the Agilent Cary 630 FTIR for both qualitative identification and quantitative determination of urea in commercial AdBlue. The goal is to develop a streamlined workflow as an alternative to the ISO 22241-2 combustion and refractive-index methods.

Methodology and instrumentation

The method comprises two parts: qualitative identification and quantitative calibration.

Qualitative identification

• Reference library creation using a 32.5% w/w urea standard.
• Spectrum comparison of commercial AdBlue against the reference via Hit Quality Index (HQI).
• Color-coded pass/fail criteria for immediate result interpretation.

Quantitative calibration

• Preparation of ten urea standards (10–60% w/w) in 10 mL volumetric flasks.
• Acquisition parameters: spectral range 4000–650 cm–1, 256 scans, 4 cm–1 resolution.
• Construction of a linear calibration curve based on the urea absorption band at ~1157 cm–1 using Agilent MicroLab Quant.
• Validation via cross-validation (total standard error ≈0.18) and independent control samples (error ≈0.19).

Used instrumentation

• Agilent Cary 630 FTIR spectrometer (ultracompact benchtop design)
• Single-reflection diamond ATR sampling module
• Agilent MicroLab Quant software (version 5.7)

Main results and discussion

Identification achieved HQI values of >0.99 for both standard and commercial AdBlue, with clear discrimination from water (HQI ≈0.82). The quantification model exhibited excellent linearity (R = 0.99934) over 10–60% w/w urea. Repeatability tests on a 32.5% w/w standard yielded <0.3% RSD, and analysis of commercial samples gave <0.6% RSD with >99% accuracy.

Benefits and practical applications of the method

The ATR-FTIR approach requires minimal sample volume, no reagents, and limited operator training. A full calibration setup takes ~30 minutes; routine analysis requires ~1.5–2.5 minutes per sample. The compact footprint and guided software workflow reduce error and support high-throughput QC in production and inspection labs.

Future trends and opportunities

Advances may include integration of chemometric models for impurity profiling, online process monitoring with flow-through ATR probes, and expansion to other exhaust fluid formulations. Automation and remote diagnostics could further boost the efficiency of SCR fluid quality assurance.

Conclusion

The Agilent Cary 630 FTIR with diamond ATR and MicroLab Quant software provides an easy-to-implement, rapid, and reliable method for both identifying and quantifying urea in AdBlue. It meets ISO 22241-2 identification requirements and offers a cost-effective alternative for routine urea determination.

References

• Foerter, D. C.; Whiteman, C. S. 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 – Suitability of Various Analytical Methods for Urea Content Determination. Int. J. Energy Res. 2020, 44, 2549–2559.