Evaluation of Cryogen-Free Thermal Modulation-Based Enantioselective Comprehensive Two-Dimensional Gas Chromatography for Stereo-Differentiation of Monoterpenes in <i>Citrus</i> spp. Leaf Oils

oleh: Haneen Ibrahim Al Othman, Atiqah Zaid, Francesco Cacciola, Zhijun Zhao, Xiaosheng Guan, Jalal T. Althakafy, Yong Foo Wong

Format: Article
Diterbitkan: MDPI AG 2023-02-01

Deskripsi

This study evaluates the applicability of enantioselective gas chromatography (<i>e</i>GC) and enantioselective comprehensive two-dimensional gas chromatography (<i>e</i>GC×GC) coupled with flame ionization detection for the stereospecific analysis of designated chiral monoterpenes within essential oils distilled from the leaves of <i>Citrus hystrix</i> (CH), <i>C. limon</i> (CL), <i>C. pyriformis</i> (CP), and <i>C. microcarpa</i> (CM). A cryogen-free solid-state modulator with a combination of enantioselective first-dimension and polar second-dimension column arrangements was used to resolve potential interferences in <i>Citrus</i> spp. leaf oils that can complicate the accurate determination of enantiomeric compositions. Interestingly, considerable variations were observed for the enantiomeric fractions (EFs) of the chiral terpenes. (+)-limonene was identified as the predominant enantiomer (60.3–98.9%) in all <i>Citrus</i> oils, (+)-linalool was the major enantiomer in CM (95.9%), (−)-terpenin-4-ol was the major isomer in CM (66.4%) and CP (61.1%), (−)-α-pinene was the dominant antipode in CL (55.5%) and CM (92.1%). CH contained (−)-citronellal (100%) as the pure enantiomer, while CL and CP have lower proportions (9.0–34.6%), and citronellal is absent in CM. The obtained enantiomeric compositions were compared and discussed with results from <i>e</i>GC using the same enantioselective column. To our knowledge, this work encapsulates the first report that details the EFs of these chiral monoterpenes in <i>Citrus</i> spp. leaf oil.