Qualitative Analysis of Triglycerides in Cooking Oil Using GC/MS

Significance of the topic

The qualitative characterization of triglycerides in cooking oils is crucial for food quality control, authenticity verification and nutritional assessment. Combining electron ionization and chemical ionization in GC/MS enables both detailed structural fragmentation and precise molecular weight determination, overcoming limitations of traditional library searches and enhancing confidence in compound identification.

Objectives and Study Overview

This study demonstrates a combined EI/CI GC/MS approach to profile triglycerides in butter oil. By leveraging complementary ionization techniques, the method aims to identify fatty acid compositions in complex natural mixtures without reliance on extensive spectral libraries.

Methodology and Instrumentation

Sample preparation:

• Commercial butter diluted to ~5% in chloroform
• 0.5 μL injected with a 50:1 split ratio

GC/MS conditions:

• Instrument: Shimadzu GCMS-QP2010 Plus
• Column: Frontier Labs UA+-65, 30 m × 0.25 mm I.D., 0.1 μm film
• Oven program: 150 °C (1 min), ramp 5 °C/min to 350 °C (20 min)
• Carrier gas: He at 45 cm/s
• Injector temp: 370 °C; interface: 350 °C; ion source: 250 °C
• EI: m/z 29–1090, 0.5 s scan interval
• CI (NH3 reagent): m/z 500–1090, 0.5 s scan interval

Key Results and Discussion

The total ion chromatograms obtained by EI and CI were equivalent, revealing multiple triglyceride peaks. Structural elucidation followed three fragmentation patterns:

1. Pattern 1 (three identical fatty acids): Peak 29 showed CI [M+NH4]+ at m/z 902 (M=884) and EI fragment m/z 603, indicating C18 fatty acids with one double bond (282 Da) at all three positions.
2. Pattern 2 (three different fatty acids): Peak 21 CI ion at m/z 824 (M=806) and EI fragments m/z 523, 551, 579 corresponded to fatty acid masses of 284, 256 and 228 Da, assigned to C18:1, C16:0 and C14:0.
3. Pattern 3 (two identical, one different): Peak 19 CI ion at m/z 796 (M=778) and EI fragments m/z 523, 551 identified fatty acids of 256 and 228 Da; intensity analysis assigned two C16:0 and one C14:0 residues.

Benefits and Practical Applications

This combined EI/CI GC/MS strategy provides accurate determination of triglyceride molecular weights and fatty acid compositions, improving reliability in food quality analysis, authenticity testing and lipid profiling without extensive database dependence.

Future Trends and Potential Applications

Advances in high-resolution mass spectrometry, rapid chromatography, and bioinformatics are poised to further enhance lipidomics workflows. Applications may expand to clinical lipid biomarker discovery, pharmaceutical development and advanced food fraud detection.

Conclusion

The integrated EI and CI approach in GC/MS offers a robust, unambiguous method for triglyceride analysis in complex oil matrices, combining detailed fragmentation data with precise molecular weight measurement.

Instrumentation

• Shimadzu GCMS-QP2010 Plus mass spectrometer
• Frontier Labs UA+-65 capillary column (30 m × 0.25 mm I.D., 0.1 μm film)
• Ammonia reagent gas for CI and helium carrier gas for GC separation