Analysis of fatty acids in a cooking oil using an On-line micro Reaction Sampler

Importance of the Topic

The accurate determination of fatty acid composition in cooking oils is essential for quality control, nutritional labeling and food safety. Traditional derivatization methods involve toxic or time-consuming reagents. Developing an efficient, reagent-free on-line approach enhances analytical throughput and reduces chemical hazards.

Objectives and Study Overview

This study aimed to evaluate an on-line micro Reaction Sampler coupled with a pyrolyzer and GC/MS for direct conversion of triglyceride-derived fatty acids into methyl esters. The performance was compared to conventional boron trifluoride (BF3) methanol derivatization in terms of composition accuracy, precision and ease of use.

Methodology

A hexane solution of commercial cooking oil was deposited in a sealed glass capsule. After solvent evaporation, methanol was added and the capsule flame-sealed. In the micro Reaction Sampler, the capsule was lowered into a pyrolyzer heated to 250 °C for 10 minutes under 7.1 MPa, promoting transesterification to fatty acid methyl esters (FAMEs). The reaction products were immediately transferred to the GC column for analysis.

Instrumentation Used

• Multi-Shot Pyrolyzer (EGA/PY-3030D)
• On-line Micro Reaction Sampler
• Vent-free GC/MS adapter
• Gas Chromatograph with split/splitless injector and mass spectrometer detector

Results and Discussion

Chromatographic analysis revealed clear detection of methyl palmitate (16:0), methyl stearate (18:0), methyl oleate (18:1), methyl linoleate (18:2) and methyl linolenate (18:3). Composition ratios determined by the on-line method closely matched those from BF3-methanol derivatization:

• 16:0 ~9.6 %, 18:0 ~3.3 %, 18:1 ~41.8 %, 18:2 ~38.2 %, 18:3 ~7.2 %
• Relative standard deviations below 3 % for all fatty acids

This indicates that high-temperature, high-pressure methanol treatment efficiently produces FAMEs with minimal isomerization and comparable precision.

Benefits and Practical Applications

The on-line micro Reaction Sampler method offers:

• Rapid, closed-system derivatization without toxic reagents
• Automated sample introduction and analysis integration
• Reduced sample handling and contamination risk

These features make it well-suited for routine QC in food laboratories and large-scale screening of edible oils.

Future Trends and Potential Applications

Advancements may include:

• Integration with high-throughput robotic platforms
• Extension to complex lipid classes and biomaterials
• Miniaturized pyrolysis modules for in-field analysis

Further optimization of reaction parameters could broaden applicability to diverse matrices such as biodiesel feedstocks and polymeric materials.

Conclusion

The study demonstrates that on-line high-temperature methanol transesterification via a micro Reaction Sampler coupled to GC/MS is a viable, efficient alternative to classical reagent-based derivatization. It delivers accurate fatty acid profiles with minimal sample preparation and environmental impact.

Reference

1. Y. Ishida et al., J. Anal. Appl. Pyrolysis, 49 (1999) 267-276.
2. S. Saka et al., J. Chem. Eng. Jpn, 34 (2001) No.3 383-387.