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

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.