Unlocking terpene enantiomeric resolution: Optimization of carrier gas and chromatographic parameters on conventional and tandem chiral columns

Abstract

Background: The separation of enantiomers via chiral gas chromatography remains a pivotal area of research in analytical chemistry, driven by its critical role in the quality control of high-value products. Recent helium shortages and escalating costs have necessitated the exploration of alternative carrier gases, such as nitrogen and hydrogen. Maintaining optimal resolution is paramount, as co-elution directly impacts the accuracy of enantiomeric ratio determination and, consequently, the reliability of analytical data. Given that resolution is a function of efficiency, selectivity, and retention, a thorough investigation of these parameters is essential to optimize enantiomeric separations when comparing different carrier gases.

Results: In this study, a comprehensive comparison of nitrogen, helium, and hydrogen as carrier gases was conducted using bergamot essential oil as a model sample on a commercially available cyclodextrin (CD) column. The analysis revealed distinct chromatographic profiles, underscoring the importance of selecting the appropriate carrier gas and chromatographic conditions for specific separation challenges. Notably, hydrogen demonstrated superior performance compared to helium, exhibiting higher resolution at elevated linear velocities. However, the analysis of a real sample highlighted significant limitations, including co-elution of chiral components with each other and with achiral compounds. To address these issues, the separation was optimized by joining two chiral stationary phases. The strategic arrangement of chiral selectors within this tandem phase column facilitated enhanced separation of critical enantiomeric pairs. This approach yielded significant improvements in enantiomer resolution, both amongst themselves and in relation to non-chiral compounds, compared to the conventional column.

Significance: These findings offer insights into the design and application of tandem chiral stationary phases for the analysis of chiral components in essential oils. The ability to fine-tune separation selectivity through the strategic combination of chiral selectors, optimization of chromatographic parameters, and judicious selection of carrier gas represents a significant advancement. This comprehensive approach provides a powerful tool for tackling challenging separations and holds broad implications for the quality control and authentication of essential oils and related products.

Keywords: Carrier gas selection; Chromatographic parameters optimization; Enantiomeric separation; Tandem chiral stationary phase; Terpenes.