A Sample Prep-Free Analysis of Triglycerides and Fatty Acids with “Smart IS+” and “SMCI+” - Authentication Studies -

Importance of the Topic

The rapid classification and identification of free fatty acids (FFAs) and triglycerides (TGs) are critical in fields ranging from food authenticity assessment to physiological research. Traditional gas chromatography/mass spectrometry (GC/MS) workflows require time-consuming derivatization steps or specialized columns. The combination of direct probe sampling with Smart IS+ and SMCI+ ionization simplifies analysis, enabling preliminary authentication studies of edible oils and advancing lipidomic investigations.

Objectives and Study Overview

This work aims to demonstrate a derivatization-free GC/MS approach for qualitative analysis of FFAs and TGs using Shimadzu’s GCMS-TQ8050 NX equipped with Smart IS+ (dual EI/PCI ion source) and SMCI+ (methanol‐mediated chemical ionization). Key goals include:

• Evaluating mass spectral patterns of six FFAs and five TGs under EI, Quick Chemical Ionization (QCI), and SMCI modes.
• Assessing elution profiles for mixtures to confirm chromatographic separation.
• Applying the method to preliminary authentication of coconut and sunflower oils.

Methodology and Instrumentation

Samples of FFAs (C10:0 to C18:1) and TGs (LLL, MMM, PPP, SSS, OOO) were prepared at 5000 ppm. One microliter aliquots were dried in a direct inlet (DI) probe, heated from ambient to 450 °C under controlled ramps. Ion source temperature was 230 °C. Mass spectra were acquired from m/z 50–900 at 3333 amu/s in three ionization modes:

• Electron Ionization (EI)
• Quick Chemical Ionization (QCI) with isobutane
• SMCI with methanol reagent gas

The GCMS-TQ8050 NX system enabled seamless switching between modes. Authentication studies used cold-pressed coconut and sunflower oils purchased locally.

Main Results and Discussion

EI spectra matched FFAs to NIST library (similarity > 85) though molecular ion peaks were weak for C10:0 and C18:1. QCI spectra of saturated FFAs showed [M+H]+ as base peak, whereas oleic acid (C18:1) presented [M–OH]+ at m/z 265. SMCI spectra revealed additional [M–OH+OMe+H]+ ions, indicating in-source methyl ester formation for saturated FFAs.
Chromatographic separation under QCI produced clear elution order for FFAs (C10:0→C12:0→C14:0→C16:0→C18:0→C18:1) below 225 °C. For TGs, EI, QCI, and SMCI spectra shared characteristic [M–FA]+ ions (e.g., m/z 183/257 for LLL, 265/339 for OOO). Elution of TGs under QCI followed LLL→MMM→PPP→OOO→SSS between 150–350 °C.
Authentication of coconut oil by SMCI displayed dominant [M–FA]+ peaks of LLL and MMM, confirming high saturated lipid content. Sunflower oil yielded OOO [M–FA]+ peaks consistent with unsaturated TG prevalence.

Practical Benefits and Applications

The Smart IS+ and SMCI+ workflows offer:

• Elimination of derivatization and specialized columns
• Rapid qualitative profiling of FFAs and TGs in complex samples
• Preliminary authenticity screening of edible oils
• Flexibility to switch ionization modes without hardware changes

Future Trends and Possibilities

Emerging directions include quantitative method development, expansion to other lipid classes (e.g., phospholipids), hyphenation with two-dimensional GC for enhanced separation, and integration into high-throughput QA/QC pipelines. Advances in reagent gas chemistries may further improve sensitivity and selectivity.

Conclusion

The combination of direct probe sampling with Smart IS+ and SMCI+ ionization on the GCMS-TQ8050 NX enables fast, derivatization-free analysis of fatty acids and triglycerides. Characteristic ion patterns and separation profiles support both qualitative identification and rapid authentication studies of vegetable oils, demonstrating a streamlined alternative for lipid analysis.