GC-MS-IRMS: Addressing authenticity of fish oils by carbon and hydrogen isotope fingerprints

Importance of the Topic

Growing consumer interest in omega-3 fatty acids has significantly expanded the global market for fish oil supplements. This surge invites economically motivated fraud, such as mislabeling of species or origin. Traditional compositional analyses often fail to distinguish oils from similar sources, creating a need for more robust authenticity tests. Stable isotope fingerprinting of carbon and hydrogen offers a powerful solution to verify geographic provenance and detect adulteration.

Objectives and Study Overview

This study aimed to evaluate compound-specific isotope analysis by combining gas chromatography, isotope ratio mass spectrometry, and quadrupole mass spectrometry (GC-MS-IRMS) to address fish oil authenticity. A total of 30 salmon oils and 43 cod liver oils were examined for δ13C and δ2H values of key fatty acid methyl esters (FAMEs). Discriminant analysis was applied to assess the ability to differentiate samples by geographical origin.

Methodology

Oil samples were converted to FAMEs via derivatization with acetyl chloride in methanol. A 1 μL aliquot was injected using a TriPlus RSH autosampler into a TRACE 1310 GC. Separation of C14 to C22 FAMEs was achieved on either a non-polar TG-5MS or a high-polar column under controlled temperature programs. Carbon and hydrogen isotope ratios were measured by a GC IsoLink II IRMS system. Simultaneously, an ISQ 7000 quadrupole MS provided compound identification and quantitative data.

Instrumentation

• Thermo Scientific TRACE 1310 Gas Chromatograph
• Thermo Scientific GC IsoLink II Interface
• Thermo Scientific ConFlo IV Universal Interface
• Thermo Scientific DELTA Series IRMS
• Thermo Scientific ISQ 7000 Single Quadrupole GC-MS
• Thermo Scientific TriPlus RSH Autosampler

Main Results and Discussion

Carbon isotope values (δ13C) for FAMEs ranged from –19.0‰ to –33.9‰ with SD < 1.1‰. Hydrogen isotope values (δ2H) ranged from –182‰ to –282‰ with SD < 3.9‰. Discriminant analysis using selected fatty acids achieved 94.3 % correct classification for salmon (Norway vs. Chile) and 97.2 % for cod (Iceland vs. Norway), demonstrating strong potential to distinguish oils from closely related regions.

Benefits and Practical Applications

• Single-injection analysis yields structural, isotopic, and quantitative information simultaneously.
• High selectivity and sensitivity supports trace-level detection of adulteration.
• Robust verification of geographic origin enhances supply chain transparency and consumer trust.

Future Trends and Applications

Expanding isotope fingerprint databases across diverse fish species and regions will increase method coverage. Integration with rapid screening platforms and machine learning could enable high-throughput authenticity monitoring. Combining isotopic data with additional biomarkers may further strengthen fraud detection and support sustainability certification.

Conclusion

This study confirms that GC-MS-IRMS provides a reliable, sensitive, and accurate approach for authenticating fish oils by carbon and hydrogen isotope fingerprints. The method effectively differentiates oils from neighboring geographic regions, offering a valuable tool against mislabeling and adulteration in the omega-3 supplement market.

References

No formal references listed.