EA-IRMS: Tracing geographical origin of Argan oil using carbon and oxygen isotope fingerprints

Importance of the topic

Argan oil is a high-value product with protected geographical indication (PGI) status from south-western Morocco, supporting local economies and millions of producers. Its popularity in food, cosmetics and pharmaceutical industries makes it a frequent target for adulteration and mislabeling. Reliable analytical methods are essential to ensure product authenticity, protect consumer confidence and guard producer reputation.

Objectives and study overview

This study demonstrates a multi-isotope fingerprinting approach using carbon (δ13C) and oxygen (δ18O) isotope ratios measured by Elemental Analysis–Isotope Ratio Mass Spectrometry (EA-IRMS) to trace the geographical origin of Argan oil. A total of 47 oil samples from diverse Moroccan regions were analyzed to establish regional isotopic signatures and assess the technique’s discriminating power.

Methodology

The analytical protocol involved two workflows on the Thermo Scientific EA IsoLink IRMS System:

• Carbon isotope analysis: Weighed 0.3 mg of oil into tin capsules, combusted in a reactor with MA Plus autosampler; CO₂ gas measured in 400 seconds per sample.
• Oxygen isotope analysis: Weighed 0.6 µL oil into silver capsules, pyrolyzed at 1450 °C; CO gas measured in 530 seconds per sample.

Instruments used

• Thermo Scientific EA IsoLink IRMS System
• MA Plus autosampler
• EA IsoLink pyrolysis reactor (ceramic tube with glassy carbon reactor)

Main results and discussion

Isotopic profiles varied significantly by region. Coastal, more humid areas (Essaouira, Agadir) yielded lower δ13C values, reflecting greater relative humidity, while the drier Taroudant region showed enriched δ13C. Oxygen isotope ratios were lower near the coast (Essaouira, Chtouka) and increased at higher altitudes, illustrating the effects of rainfall depletion inland and altitude. Plotting δ13C against δ18O enabled clear clustering of samples by geographic origin, influenced by climate, altitude and proximity to the High Atlas mountain barrier.

Benefits and practical applications of the method

This isotopic approach provides a rapid, robust tool for verifying the provenance of Argan oil. By distinguishing regional signatures, it helps detect adulteration and mislabeling, thereby safeguarding producer PGI status and ensuring consumer trust.

Future trends and potential applications

Expanding the isotope dataset to include hydrogen or nitrogen isotopes could enhance discrimination. Building a comprehensive isotopic database for Argan oil and other regional products will improve authentication frameworks. Integrating this method with molecular or metabolomic profiling could further resolve fine-scale geographic origins and combat sophisticated fraud.

Conclusion

EA-IRMS carbon and oxygen isotope fingerprinting successfully differentiates Argan oils from distinct Moroccan regions. The method links isotopic variations to environmental factors, offering an effective strategy for authenticity and provenance verification in high-value agricultural products.

References

• Taous F, Amenzou N, Marah H, Maia R, Maguás C, Bahmad L, Kelly S. 2020. Forensic Chemistry.
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