Structural Elucidation of an Unknown Compound in the Fatty Acid Methyl Esters (FAMEs) Extract of Avocado Using APGC-HRMS

Significance of the Topic

Avocado oil and fats contain a complex mixture of fatty acids whose accurate profiling is essential for nutrition research, quality control, and food safety.
Conventional GC-FID methods may overlook unexpected lipid constituents that could affect product quality or consumer health.

Objectives and Study Overview

This study applied atmospheric pressure gas chromatography paired with high-resolution mass spectrometry (APGC-HRMS) and integrated data analysis to:

• Confirm known fatty acid methyl esters (FAMEs) in an avocado extract
• Detect and structurally elucidate an unknown chromatographic peak

Methodology

An avocado fat extract was prepared by acid hydrolysis and Mojonnier extraction, then converted to FAMEs via NaOH/MeOH/BF3 derivatization.
One microliter of a 1:1000 heptane dilution was injected in splitless mode onto a DB-5MS column using an Agilent 7890 GC with a 100°C to 240°C temperature ramp.
APGC ionization with a water dopant generated predominantly [M+H]+ ions.
Data were acquired in MS E mode (low energy 6 eV, high energy 20–50 eV) on a Waters Xevo G2-XS QTof, covering m/z 50–1000.
Processed in the UNIFI Scientific Information System with automated lockmass correction.

Instrumentation

• Waters Xevo G2-XS QTof high-resolution mass spectrometer
• Atmospheric pressure gas chromatography (APGC) universal source
• Agilent 7890 GC with DB-5MS 30 m×0.25 mm, 0.25 µm column
• UNIFI Scientific Information System and Discovery Toolset

Main Results and Discussion

Five target FAMEs (C16:0, C16:1, C18:1 cis/trans, C18:2) were confirmed within ±3 ppm mass error using extracted ion chromatograms and MS E fragmentation matching.
Characteristic fragments included the loss of the methyl ester group (m/z 265.253) and series of alkyl chain cleavages with hydride abstraction clusters.
An unexpected peak at 31.29 min, m/z 303.2683, was interrogated in the UNIFI Discovery Toolset.
Elemental composition, isotope pattern scoring, ChemSpider search, and high-energy fragment matching proposed 3-pentadecenylphenol.
Key fragments included an intact benzene ring and loss of water (m/z 285.258).
Cross-referencing FooDB confirmed this compound in cashew and ginkgo lipids, supporting a tentative identification.

Benefits and Practical Applications

APGC soft ionization preserves molecular ions while MS E provides comprehensive fragmentation, enabling confident identification of known and unknown lipids.
Integrated UNIFI workflows streamline database searches, fragment annotation, and structural proposals without offline tools.
This approach enhances quality control, authenticity testing, and safety assessments in food and lipid research.

Future Trends and Potential Applications

Expansion of high-resolution spectral libraries and automated spectral matching will accelerate unknown compound discovery in complex matrices.
Combining APGC-HRMS with orthogonal techniques and reference standards will improve structural confirmation and quantification.
Real-time data processing and machine learning integration may further reduce turn-around time for food safety screenings.

Conclusion

The described APGC-HRMS method paired with UNIFI software effectively profiles FAMEs and elucidates unexpected lipid constituents in avocado extracts.
This workflow supports high-confidence structural assignments and can be adapted to a range of food and biological matrices.

References

• 1. Duarte PF, Chaves MA, Borges CD, Mendonca CR. Avocado: characteristics, health benefits and uses. Food Technol. 2016;46(4):747–754.
• 2. Sigma-Aldrich. Analytical chromatography products.
• 3. MS-Textbook. Chapter 7: hydride abstraction processes.
• 4. FooDB. Compound FDB002351: 3[(8Z)-8-pentadecen-1-yl]phenol.