Determination of FAME in Biodiesel blends using FTIR

Importance of the Topic

Biodiesel, composed of fatty acid methyl esters (FAME), is a sustainable diesel substitute that reduces particulate emissions and offers superior lubricity. Accurate quantification of FAME in diesel blends is essential for meeting regulatory labeling requirements (up to B5 in Europe and the US) and ensuring product quality throughout production and distribution.

Objectives and Study Overview

This application note demonstrates a rapid FTIR-based method for determining FAME concentration in diesel blends according to DIN EN 14078. The aim is to establish calibration models, evaluate sensitivity, and illustrate a user-friendly workflow for both low (0.02–1 % m/m) and standard (0–5 % m/m) concentration ranges.

Methodology

The analysis exploits the pronounced carbonyl absorption band at ~1745 cm⁻¹, unique to esters and absent in petrodiesel. A univariate linear calibration based on the Lambert-Beer law correlates absorbance with FAME content. Two path lengths (100 and 500 µm) enable measurement ranges of 0–5 % m/m and 0.02–1 % m/m respectively. Samples may be diluted for higher concentrations and measured in transmission using a liquid flow-through cell.

Instrumentation Used

• Bruker ALPHA II FTIR spectrometer with RockSolid interferometer and diode laser
• Liquid flow-through cuvettes with 100 µm and 500 µm spacers
• Dedicated FAME-in-diesel software wizard for calibration, path length detection, dilution correction, and autosampler control
• Optional compatibility with INVENIO and VERTEX spectrometers

Key Results and Discussion

Calibrations in the 0–5 % m/m range yielded a correlation coefficient of 0.9999 and standard deviation of 0.017 % m/m. The shorter-path 500 µm cell achieved a correlation of 1.0000 and standard deviation of 0.003 % m/m for 0.02–1 % m/m. Detection limits down to 0.02 % m/m were confirmed. Typical analysis time, including background, is under four minutes per sample.

Benefits and Practical Applications

• High throughput: less than two minutes per measurement
• Minimal sample preparation with simple dilution
• Automatable for large sample series using an autosampler
• Robust, compact instrumentation operable by non-specialists
• Automatic PDF reporting compliant with DIN EN 14078

Future Trends and Applications

Advancements may include inline process monitoring, integration of chemometric algorithms for multivariate analysis, expanded spectral libraries for broader fuel components, and digital connectivity for remote quality control in smart refineries.

Conclusion

FTIR spectroscopy with a liquid flow-through cell provides a fast, accurate, and robust solution for FAME quantification in diesel blends. The method meets regulatory standards and supports both routine QA/QC and automated high-throughput applications.

Reference

1. Bruker Optics. Application Note AN M60: Determination of FAME in Biodiesel Blends Using FTIR. 2021.