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

Importance of the Topic

A rise in demand for omega-3 fish oil supplements has created opportunities for economically motivated fraud, including mislabelling and adulteration. Traditional fatty acid profiling often fails to distinguish oils from different species or geographic regions. Compound-specific stable isotope analysis provides a robust tool for verifying origin and authenticity, bolstering consumer confidence and regulatory compliance.

Objectives and Study Overview

This study applied gas chromatography-mass spectrometry-isotope ratio mass spectrometry (GC-MS-IRMS) to:

• Measure carbon (δ13C) and hydrogen (δ2H) isotope fingerprints of fatty acids in fish oils.
• Discriminate between Atlantic salmon oils from Norway and Chile.
• Differentiate Arctic cod liver oils from Iceland and Norway.

Methodology and Instrumentation

Sample Preparation:

• Derivatization of fish oil triglycerides to fatty acid methyl esters (FAMEs) using CH3COCl in MeOH.
• 1 µL injection via an automated TriPlus autosampler.

Analytical Configuration:

• Thermo Scientific TRACE 1310 GC with non-polar and high-polar capillary columns.
• Thermo Scientific GC IsoLink II interface to ConFlo IV.
• Thermo Scientific DELTA V IRMS coupled to a single quadrupole MS for simultaneous isotope and structural data.

Key Results and Discussion

Salmon Oils:

• δ13C values ranged from –19.0‰ to –33.9‰ (TDEV <1.1‰).
• δ2H values ranged from –182‰ to –282‰ (TDEV <3.9‰).
• Discriminant analysis achieved 94.29 % correct classification of Norway vs. Chile samples.

Cod Liver Oils:

• Similar isotope ranges reflecting diet and habitat.
• Discrimination between Icelandic and Norwegian cod gave 97.22 % correct predictions.

This demonstrates that compound-specific δ13C and δ2H fingerprints effectively resolve geographic origin even for closely related stocks.

Benefits and Practical Applications

The GC-MS-IRMS approach offers:

• High selectivity and sensitivity from a single injection.
• Simultaneous structural identification and isotope ratio measurement.
• Reliable authenticity testing to support traceability, quality control, and regulatory enforcement in the fish oil industry.

Future Trends and Potential Applications

Emerging directions include:

• Extending multi-isotope profiling (e.g., N, O, S isotopes) for broader food authenticity challenges.
• Applying the method to other high-value marine products and botanical oils.
• Integrating machine learning for automated pattern recognition and rapid screening.

Conclusion

GC-MS-IRMS with compound-specific isotope analysis provides a powerful and validated tool for determining fish oil provenance. The demonstrated high classification accuracy for salmon and cod liver oils underscores its value for combating fraud and ensuring product integrity.