Portable measurement of biodiesel in diesel fuels by ASTM D7371-07 (FTIR- ATR-PLS method) with the Agilent 5500t FTIR spectrometer

Importance of the Topic

With tightening emission regulations and rising demand for renewable fuels, determining the precise biodiesel content in ULSD blends is essential for quality control and regulatory compliance. A rapid, portable, and accurate technique supports both large-scale distributors and on-site field operators.

Study Objectives and Overview

This study applies the ASTM D7371-07 method using FTIR-ATR combined with PLS chemometrics to quantify fatty acid methyl ester (FAME) content from 1% to 100% in diesel. Calibration and validation sets account for seasonal variations in diesel cetane index.

Methodology and Instrumentation

• Sample Preparation: ASTM-certified B100 biodiesel blended with ULSD at three cetane indices (low, high, ultra-high) yielding 70 calibration and 21 qualification standards spanning 0–100% FAME.
• Spectral Acquisition: Agilent 5500 Series FTIR spectrometer with 9-reflection diamond ATR, 64 scans, 4 cm⁻¹ resolution, 30 s measurement per sample.
• Chemometric Model: Partial least squares regression (Thermo Galactic PLS/IQ), focusing on ester carbonyl (1741 cm⁻¹) and C–O bands (1170–1245 cm⁻¹), integrated into Agilent Microlab software.

Key Results and Discussion

• Linearity: Strong correlation (R² = 0.999) for the 0–10% range, with comparable performance for 10–30% and 30–100% models.
• Accuracy: Qualification set yielded an average relative error of 0.47% and a maximum of 1.56%, well below the ASTM SEQ limit of 0.21%.
• Software Logic: Microlab automates model selection and conditional reporting, presenting a single, unambiguous FAME concentration.

Practical Benefits and Applications

• Portability and Speed: Enables on-site analysis in under one minute per sample without extensive training.
• Robustness: Accommodates fuel variations due to seasonal cetane index changes.
• Quality Assurance: Ideal for production facilities, distribution centers, and regulatory agencies monitoring biodiesel blends.

Applied Instrumentation

• Agilent 5500 Series FTIR Spectrometer
• 9-reflection diamond ATR sample interface
• Agilent Microlab software with embedded PLS models

Future Trends and Opportunities

• Extension to other bio-blend analyses, such as ethanol or renewable hydrocarbon additives.
• Integration with wireless data reporting and cloud-based QC platforms.
• Enhanced chemometric approaches using evolving machine-learning algorithms for improved robustness.

Conclusion

The Agilent 5500 FTIR-ATR method with ASTM D7371-07 PLS models delivers a simple, accurate, and portable solution for quantifying biodiesel across the full concentration range. Its speed, precision, and ease of use make it a valuable tool for industry and regulators.

References

• ASTM D7371-07 Standard Test Method for Determination of Biodiesel (FAME) Content in Diesel Fuel
• Higgins, F., Agilent Technologies Application Note 5990-7807EN, 2011