Biodiesel analysis: Biofuel blend by NMR spectroscopy

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  • Published: Apr 15, 2017
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
thumbnail image: Biodiesel analysis: Biofuel blend by NMR spectroscopy

Counting on biodiesel

Counting on biodiesel, cheminformatics analysis of NMR spectra detects vegetable oil Photo credit: CC via Flickr user Gustavo Gomes

A new quantitative method of analysing the biodiesel in a diesel-biodiesel blend using proton nuclear magnetic resonance (NMR) spectroscopy has been developed by researchers in Brazil. The resulting spectra are subjected to a univariate calibration in which the integrals of the spectra are considered. Statistical comparison with infrared (IR) spectra corroborate the findings.

Biodiesel in biodiesel blended fuels are an important part of efforts to cut down our reliance on fossil fuels and to create a sustainable transport system. Many cities and whole regions have adopted biofuels on a large scale for public transport and even private transport. However, there is always room for fraud in any human endeavour and the addition of raw vegetable oil rather than processed, transesterified oil, is rife in the market for biofuels. Although even in the absence of fraud there is always the possibility of inadequately processed vegetable oil being added to a blend with the same end result, sooty, polluting, and inefficient fuel combustion.

Fuel validation

Gustavo Shimamoto, Luis Bianchessi, and Matthieu Tubino of the Institute of Chemistry, University of Campinas (UNICAMP) in Brazil explain that their proposed proton NMR spectroscopic approach to biodiesel verification is not only valid against European Standard EN 14078 IR spectroscopic analysis but also shows that the NMR method can easily spot the difference between biodiesel and vegetable oil, something that cannot actually be discerned using IR spectroscopy alone. "The proton NMR method is a more practical and efficient alternative to the official method," the team writes in the journal Talanta (The International Journal of Pure and Applied Analytical Chemistry).

The team explains that Brazil is one nation at the forefront of adopting biodiesel. The bio component of commercial diesel has increased from2 percent by volume in 2008 to close to 10 percent currently, with 10% being the definitive target by 2019. Univariate and multivariate calibrations of IR spectra are the standard for quality analysis of biodiesel blends but these do not detect cheap contaminants such as vegetable oil. Not only does vegetable oil lower the quality of the fuel and increase pollution it can lead to damage to engines and so its detection, whether inadvertent or illegal is important if the adoption of biodiesel is to be an ongoing process towards greater sustainability of transport.

Spectral confidence

Critical is the fact that vegetable oil or poorly transesterified oil may be added at a late stage before it is pumped into vehicles and so any analytical technique used to detect contamination at any stage must be sufficiently robust to cope with a range of sample types.

NMR spectroscopy is expensive but it is fast and the team has now proven it to be sufficiently robust in this context, indeed only a simple proton NMR spectrum is needed. Analysis is carried out with a 95% confidence level, the team reports.

Related Links

Talanta 2017, online: "Alternative method to quantify biodiesel and vegetable oil in dieselbiodiesel blends through 1H NMR spectroscopy"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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