Determination of Fatty Acid Methyl Esters by GCxGC-TOFMS

Significance of the Topic

The composition of fatty acids in food products critically affects human health. Saturated fats and trans fatty acids raise LDL cholesterol and risk of atherosclerosis, while cis and polyunsaturated fatty acids lower it. Reliable profiling of fatty acid methyl esters (FAMEs), especially for trans isomers, supports nutritional monitoring and regulatory compliance.

Objectives and Study Overview

This study aimed to develop a comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS) method for FAME analysis, compare it to one-dimensional GC-TOFMS, and apply it to real food samples (flaky pastry and egg) to quantify 37 FAMEs.

Experimental Methodology and Instrumentation

Standards and real samples were derivatized to FAMEs and analyzed under two configurations:

• 1D GC-TOFMS: Agilent 6890N GC, DB-5MS column (30 m×0.25 mm×0.25 µm), 1 µL split injection, helium carrier, LECO Pegasus 4D TOFMS at 70 eV (45–650 u), 2 spectra/s acquisition.
• GC×GC-TOFMS: Agilent 6890N with LECO thermal modulator and secondary oven, DB-5MS primary column (30 m×0.25 mm×0.25 µm) and BPX-50 secondary column (2 m×0.1 mm×0.1 µm), same injection and carrier settings, modulation time 5 s, hot pulse 1 s, 100 spectra/s acquisition.

Temperature programs were optimized to achieve full elution of C6–C24 FAMEs and linear contour plots based on volatility and polarity.

Main Results and Discussion

GC×GC-TOFMS delivered enhanced separation compared to 1D GC-TOFMS. Optimization with BPX-50 in the second dimension achieved linear elution of all FAMEs under a 300 °C program. Contour plots ordered FAMEs by carbon number (X-axis) and double bond count (Y-axis). Deconvolution software correctly resolved coeluting isomers (e.g., gamma-linolenic, oleic, linoleaidic). In real samples, GC×GC contour plots rapidly highlighted key C18 FAMEs and quantified 37 analytes, revealing higher trans-elaidic content in pastry than in egg.

Benefits and Practical Applications

• Baselined separation of all FAMEs, including trans isomers, in a single run.
• Structured contour plots facilitate identification by volatility and polarity without additional MS libraries.
• Automated deconvolution and quantification streamline analysis of complex food matrices.
• Potential adaptation for routine GC×GC-FID workflows in QA/QC laboratories.

Future Trends and Potential Applications

Expected developments include integration with high-resolution MS or tandem MS for improved selectivity, further automation of data processing, expansion to other lipid classes, and broader adoption in regulatory monitoring and nutritional research.

Conclusion

The GC×GC-TOFMS method provides robust, high-resolution analysis of fatty acid methyl esters, outperforming one-dimensional approaches and enabling comprehensive profiling of cis and trans isomers in food samples.

Reference

• LECO Corporation. Determination of Fatty Acid Methyl Esters by GC×GC-TOFMS. St. Joseph, MI: LECO Corporation; 2008.