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

The measurement of biodiesel concentration in diesel fuels is critical for regulatory compliance, engine performance optimization, and quality assurance. The ASTM D7371-07 standard provides a reliable framework to quantify biodiesel content from 1–100% by volume, enabling both large fleet operators and individual users to verify blend specifications on site.

Objectives and Study Overview

The study aimed to develop a portable, rapid, and accurate method for quantifying biodiesel in diesel blends using an Agilent 5500 Series FTIR spectrometer. Calibration and qualification standards covering seasonal variations in diesel cetane index were prepared to validate the ASTM D7371 procedure across B5, B10, B20, and higher blends.

Methodology and Instrumentation

Calibration standards were produced by mixing certified B100 biodiesel with ULSD at three cetane index levels (low, high, ultra-high) to generate 70 samples spanning 0–100% biodiesel. An additional 21 qualification samples with varied concentrations tested method accuracy.

The analytical workflow comprised:

• FTIR-ATR measurement using 64 scans at 4 cm–1 resolution (30 seconds per sample).
• Partial least squares (PLS) modeling focusing on the ester carbonyl band at 1741 cm–1 and the 1170–1245 cm–1 region characteristic of FAME.
• Implementation of three separate calibration models (0–10%, 10–30%, 30–100%) within Microlab software for conditional reporting of results.

Used Instrumentation

The key instrument employed was the Agilent 5500 Series FTIR spectrometer equipped with a nine-reflection diamond attenuated total reflectance (ATR) interface. Data processing and model deployment were performed with Thermo Galactic PLS/IQ software integrated into Microlab.

Key Results and Discussion

Spectral analysis revealed linear increases in FAME absorbance at diagnostic bands across the full concentration range. The PLS models achieved outstanding correlation (R2=0.999 for the 0–10% range) using 3–4 factors on mean-centered data. Qualification tests yielded an average relative error of 0.47% and a maximum error of 1.56%, with a standard error of qualification (0.08%) well below the ASTM D7371 limit (0.21%).

Practical Benefits and Applications

This FTIR-ATR-PLS approach offers:

• Rapid analysis (30 seconds per sample) suitable for high-throughput testing.
• Portable operation enabling field or dockside verification of biodiesel blends.
• Simplified user interface in Microlab allowing untrained personnel to obtain accurate results.

Future Trends and Opportunities

Advances may include expanding PLS libraries for alternative biofuels, integrating cloud-based data management for real-time fleet monitoring, and miniaturizing spectrometer hardware for handheld use. Enhanced chemometric algorithms could further reduce sample variability and extend applicability to complex fuel matrices.

Conclusion

The integration of ASTM D7371-07 with the Agilent 5500 FTIR-ATR system provides a validated, user-friendly method for quantifying biodiesel in diesel fuels. The method demonstrates high precision, low error, and rapid turnaround, supporting quality control across production, distribution, and end-use environments.

References

• ASTM International. D7371-07 Standard Test Method for Determination of Biodiesel Fuel (FAME) Content in Diesel Fuel Oils by FTIR Using ATR. 2007.