Determination of Fatty Acids in Foods Using Gas Chromatography with Positive-ion Chemical Ionization Tandem Mass Spectrometry

Significance of the Topic

Fatty acids are key nutritional and functional constituents in food products. Their detailed profiling supports food quality control, nutritional labeling and detection of adulteration. However, complex food matrices and co-eluting interferences demand analytical methods with high sensitivity and selectivity to reliably quantify both saturated and unsaturated fatty acids.

Study Objectives and Overview

This work evaluates four analytical strategies for fatty acid methyl ester analysis by gas chromatography–mass spectrometry: GC-EI-MS, GC-PICI-MS, GC-EI-MS/MS and GC-PICI-MS/MS. The goal is to compare limits of quantitation, interference separation and performance in a real food sample.

Methodology and Instrumentation

Sample Preparation and Derivatization:

• 200 mg ground fish meat extracted with organic solvent and centrifuged.
• Supernatant dried under nitrogen and methylated using a commercial kit at 37 °C.
• Purified methyl esters obtained via liquid–liquid extraction and cleanup.

Chromatographic and MS Conditions:

• Shimadzu GCMS-TQ8030 with SP-2560 column (100 m × 0.20 mm, 0.25 µm).
• Injector at 250 °C; oven ramp from 40 °C to 240 °C.
• Ionization: EI at 70 eV; positive-ion chemical ionization (PICI) using isobutane at 70 kPa.
• Detection modes: SIM and MRM with Ar collision gas (200 kPa) and optimized collision energies.

Key Results and Discussion

• Limit of Quantitation: PICI-SIM and PICI-MRM achieved lower LOQs for all 37 fatty acids versus EI modes, particularly improving unsaturated fatty acid detection by over twofold in many cases.
• Selectivity: EI spectra produced numerous low-abundance fragments and co-eluting interferences, limiting monitoring ion choice. PICI generated strong quasi-molecular ions, enhancing sensitivity, while MRM further improved selectivity by targeting unique precursor–product transitions.
• Matrix Separation: In fish extract, PICI-MRM resolved overlapping peaks effectively, whereas EI-SIM and EI-MRM showed poor separation of isobaric compounds.

Benefits and Practical Applications

• Enhanced detection of trace fatty acids in complex foods aids regulatory testing and authenticity assessments.
• MRM mode reduces false positives and improves confidence in compound identification for QA/QC laboratories.
• PICI-MRM streamlines multi-component profiling, reducing analysis time compared to multiple SIM runs.

Future Trends and Potential Uses

• Coupling PICI with high-resolution mass spectrometry to further elevate selectivity and structural elucidation.
• Automated, on-line derivatization and sample preparation for high-throughput applications.
• Extension to broader lipidomics workflows encompassing intact lipids and complex lipid classes.

Conclusion

Positive-ion chemical ionization tandem MS in MRM mode (PICI-MRM) delivers superior sensitivity and selectivity for both saturated and unsaturated fatty acids compared to EI-based methods. It is recommended for routine fatty acid analysis in food research and quality control environments.

References

• Kawana S., Kudo Y., Sakamoto Y., Nakagawa K., Chambers L., Whitney R., Miyagawa H. Determination of Fatty Acids in Foods Using Gas Chromatography with Positive-ion Chemical Ionization Tandem Mass Spectrometry. ASMS 2013, ThP-201.