Analysis of the sesquiterpene fraction of citrus essential oils by using the off‐line combination of high performance liquid chromatography and gas chromatography‐based methods: a comparative study

Abstract

The present investigation is based on the off-line combination of high-performance liquid chromatography (HPLC), with different high-resolution gas chromatography (GC) methods (LC//GC), for the analysis of the sesquiterpene hydrocarbon (SH) fraction of various Citrus essential oils. Attention was directed to such constituents because the SH profile is often highly specific and can vary considerably between different Citrus oil-types. The (normal phase) HPLC step was exploited for the separation of the hydrocarbons, from the oxygenated compounds, hence generating a simplified sub-sample. After, the hydrocarbon fraction was concentrated and subjected to analysis, using conventional GC-quadrupole mass spectrometry (qMS) and GC-flame ionization detection (FID), comprehensive two-dimensional GC-qMS and comprehensive two-dimensional GC-FID, and cold-injection GC-qMS. The latter approach was exploited to avoid and evaluate solute rearrangements occurring under hot-injection conditions. The data derived from each approach were compared, to evaluate each analytical approach. Apart from the comparative scopes, an overall highly-detailed view (both qualitative and quantitative) was attained on the SH fraction of each essential oil, with many constituents reported here for the first time.

In-Depth Qualitative Analysis of Lime Essential Oils Using the Off-Line Combination of Normal Phase High Performance Liquid Chromatography and Comprehensive Two-Dimensional Gas Chromatography-Quadrupole Mass Spectrometry

“…Six hydrocarbons (all aliphatic) reported in Table 1, to the best of the present authors’ knowledge, have not been previously reported in the literature (an in-depth investigation was carried out) in a cold-extracted lime oil. Furthermore, γ-elemene (a sesquiterpene) was found for the first time in Persian oil, even though it has been reported in Key A and B oils [2,10]. Five hydrocarbons were found in both types of Key oils (undecane, tetradecane, pentadecane, hexadecane, heptadecane), while six (tetradec-1-ene, tetradecane, γ-elemene, pentadecane, hexadecane, heptadecane) were present in the Persian oil.…”

“…Abbreviations: M: monoterpene; Ali: aliphatic; S: sesquiterpene. a Compound not yet identified in cold-extracted laboratory oils [2,10]. b Compound identified in only one of the samples.…”

“…b Compound identified in only one of the samples. c Compound identified previously in industrially cold-extracted lime oils and cold-extracted laboratory oils, reported since 1980 [2,10]. d Compound identified previously only in cold-extracted laboratory oils [2,10].…”

“…With the aim of exploiting the benefits of both LC and GC × GC (with single quadrupole (Q) MS), in previous off-line research the two technologies were combined (LC//GC × GC-QMS) and used for the highly-detailed qualitative analysis of sweet orange and bergamot essential oils [9]. Later studies were focused on a highly specific albeit minor chemical class (sesquiterpene hydrocarbons) of lemon, bergamot, sweet orange, clementine, bitter orange, mandarin (green, yellow, red), pink grapefruit, and lime (Key A, Key B, and Persian) essential oils [10], and on the oxygenated constituents of green, yellow, and red mandarin oils [11].…”

Stereoselective Synthesis of the Spirocyclic Ring System of the Sesquiterpene Spirolepechinene

“…It has since been tentatively identified in several other plant-based sources. [7][8][9][10] Spirolepechinene has a unique relative stereochemistry about its spirocentre. The two other members of the spirojatamane class, erythrodiene and spirojatamol have epimeric relative configuration about their spirocentres compared to spirolepechinene.…”