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

Importance of the topic

Rising demand for omega-3 fish oil supplements is accompanied by increased risk of fraud through mislabelling and adulteration. Robust analytical methods for verifying species, geographic origin and authenticity are critical for consumer protection and industry integrity.

Objectives and Study Overview

This study applied compound-specific carbon and hydrogen isotope analysis by gas chromatography–isotope ratio mass spectrometry (GC-IRMS) coupled with quadrupole MS to 30 salmon oils and 43 cod liver oils. The goal was to discriminate geographic provenance and detect potential mislabelling based on stable isotope fingerprints.

Methodology and Instrumentation

Oil samples were converted to fatty acid methyl esters (FAMEs) via derivatization with acetyl chloride in methanol. A single injection (1 µL) was separated on non-polar and high-polarity capillary columns under a stepped temperature program. A GC-IRMS system with automated switching between carbon and hydrogen isotope analysis provided δ13C and δ2H values for each FAME. Concurrently, a quadrupole mass spectrometer enabled qualitative compound identification.

• Derivatization agent: CH3COCl in MeOH
• Injection volume: 1 µL
• Columns: 30 m × 0.25 mm i.d. (0.25 µm) non-polar TG-5MS and 60 m × 0.32 mm i.d. (0.25 µm) high-polarity
• Carrier gas: Helium at 1.8 mL/min
• Temperature program: 100 °C initial, gradient to 330 °C
• Instrument configuration: Thermo Scientific GC IsoLink II IRMS, TRACE 1310 GC, ConFlo IV interface, DELTA V IRMS with quadrupole MS

Main Results and Discussion

Salmon oils exhibited δ13C values from –19.0‰ to –33.9‰ (±1.1‰) and δ2H values from –182‰ to –282‰ (±3.9‰). Discriminant analysis correctly classified Norwegian vs. Chilean samples with 94.3% accuracy. Cod liver oils showed similar isotopic ranges; classification of Arctic cod from Iceland vs. Norway reached 97.2% accuracy, despite close geographical proximity.

Benefits and Practical Applications

The compound-specific multi-isotope GC-IRMS approach enables simultaneous structural, quantitative and isotopic information from a single injection. It offers high selectivity, sensitivity and confidence for food authenticity testing, ensuring reliable verification of label claims and provenance in high-value fish oil products.

Future Trends and Potential Applications

Integration of additional isotope systems such as nitrogen and oxygen, expansion to other lipid-rich matrices, and further automation of data analysis could enhance throughput and discrimination power. Combining isotopic fingerprints with chemometric modeling and blockchain-based traceability may strengthen supply chain transparency.

Conclusion

GC-IRMS coupled with MS provides a powerful, accurate tool for determining fish oil origin and detecting fraud. High classification rates for geographically close samples demonstrate its robustness. Adoption of this method can safeguard product authenticity and consumer trust in the omega-3 supplement market.

Reference

• Mario Tuthorn, David Psomiadis, Balazs Horvath, Maria de Castro. GC-MS-IRMS: Addressing authenticity of fish oils by carbon and hydrogen isotope fingerprints. Thermo Fisher Scientific.