Compositional analysis of polyunsaturated fatty acid oil by one-stepthermally assisted hydrolysis / methylationin the presence of trimethylsulfonium hydroxide (TMSH)

Importance of the Topic

Polyunsaturated fatty acid composition in oils is critical for nutritional, industrial, and regulatory applications. One-step thermally assisted hydrolysis and methylation (THM) streamlines sample preparation and increases throughput for the analysis of lipid profiles. However, using strong alkaline reagents like TMAH in THM can cause isomerization of PUFAs.

Objectives and Study Overview

This study evaluates a one-step THM–GC method employing trimethylsulfonium hydroxide (TMSH) to accurately profile fatty acid compositions in oils, with emphasis on preserving PUFA integrity. Method performance was benchmarked against offline transmethylation and TMAH-based THM protocols using triarachidonin, soybean oil, and sardine oil samples.

Methodology

Samples were subjected to pyrolysis at 350°C in the presence of varying concentrations of TMSH or TMAH. The reaction generated fatty acid methyl esters (FAMEs) in situ, which were directly analyzed by GC. Offline transmethylation with TMSH followed by GC served as a reference method.

Used Instrumentation

• Pyrolysis–Gas Chromatograph (Py–GC) with capillary column
• Flame Ionization Detector (FID) and Mass Spectrometer (MS)
• Pyrolysis temperature: 350°C

Main Results and Discussion

TMSH-based THM produced chromatograms with minimal isomer peaks for C18:2 and C18:3, whereas TMAH induced significant isomerization. At 0.2 M TMSH, fatty acid profiles matched offline GC results, with recoveries around 80% for each component. Analysis of sardine oil confirmed method reproducibility and accuracy relative to traditional GC methods.

Practical Benefits and Applications

• Rapid, one-step derivatization and analysis of lipids without extensive sample prep
• Preservation of PUFA structural integrity, essential for nutritional quality assessment
• Consistent recoveries enable reliable quantitation in food quality control, research, and industrial labs

Future Trends and Opportunities

Integration with advanced detectors such as tandem MS could enhance isomer resolution and trace component analysis. Automated pyrolyzer–GC interfaces and novel derivatizing reagents may further streamline workflows for high-throughput lipidomics. Applications may expand to complex biological and environmental matrices.

Conclusion

One-step THM–GC using TMSH offers a robust, accurate, and efficient approach for compositional analysis of PUFA-rich oils, overcoming the isomerization drawbacks of conventional bases. This method aligns with modern analytical demands by simplifying sample preparation and ensuring reliable quantitation.

References

1. Y. Ishida et al., Journal of Analytical and Applied Pyrolysis, 49 (1999) 267–276