Posted by Ivan Wortman on Sep 11, 2025
Biodiesel is a renewable alternative to fossil diesel, but its oxidative degradation remains a major obstacle. This process, driven by free radicals, reduces stability, increases acidity, and threatens engine performance.
Here, we highlight three important studies that applied ESR to biodiesel research — from tracking free radical formation to evaluating the role of antioxidants.
This pioneering work applied ESR with spin trapping to monitor free radicals in biodiesel made from corn, soybean, and commercial blends. The technique successfully revealed the three stages of oxidative degradation: initiation, propagation, and termination.
The researchers also compared ESR data with Rancimat results. They found that the ESR induction period (EIP) matched the oxidative stability rankings obtained from Rancimat but required far less time.
Conclusion: ESR was a fast, sensitive, and inexpensive tool for assessing biodiesel degradation and stability.
Notable Quote: "Electronic paramagnetic resonance (EPR) monitoring via spin trapping demonstrated to be a valuable tool in the study of radical reactions in biodiesel, since the formed free radicals are unstable and difficult to detect."
🔗Read the paper here.
Building on earlier work, this study used ESR to examine how antioxidants influence biodiesel degradation over time. The researchers quantified how different antioxidants delayed radical formation and reduced hydroxyl radical signals during the oxidation process.
These ESR findings aligned closely with conventional stability metrics, such as induction period and acidity number, confirming that antioxidants extend biodiesel’s usable life by slowing radical-driven reactions.
Conclusion: ESR provided direct quantitative evidence of antioxidant action, reinforcing its role as a diagnostic and quality-control tool in biodiesel stability studies.
Notable Quote: "The EPR demonstrated to be efficient in the evaluation of the degradation reaction in different biodiesel samples by observing PBN adduct radicals over time."
🔗 Read the paper here.
Ferrari’s study focused on how nitroxide-based antioxidants (redoxomas) protect biodiesel from oxidative degradation. The team tested compounds such as Tempol (R01) and Redoxoma R17 to assess their ability to stabilize soybean biodiesel.
Using EPR (Electron Paramagnetic Resonance) with the DPPH radical assay, along with UV-Vis spectroscopy and the Rancimat method, the researchers compared how these additives neutralized free radicals. Results from EPR and UV-Vis aligned closely with the Rancimat stability test, confirming the reliability of the spectroscopic approaches. Among the additives, Redoxoma R17 provided the strongest protective effect, performing on par with Tempol in extending biodiesel stability.
Conclusion: EPR enabled sensitive monitoring of radical suppression, proving to be valuable for comparing antioxidant performance.
Note that this technical paper was translated to English and then reviewed.
Across these three studies, ESR emerges as a central method for biodiesel research:
Together, these insights show that ESR is not only deepening our understanding of biodiesel chemistry but also paving the way for more stable, sustainable fuels.
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Disclaimer: This article is provided for informational purposes only. The ESR5000 is a scientific research instrument. Its use in quality control, regulatory, or medical contexts depends on customer validation and applicable standards.
This article was written in part with the assistance of AI to help organize, summarize, and reference publicly available information.
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