Chromatographic Conditions as a Source of Analytical Variability in GC–MS Profiling of Essential Oils

The analytical characterization of essential oils (EOs) is often interpreted primarily in terms of biological variability, although analytical conditions may also affect compositional profiling and data comparability. In this study, the influence of chromatographic conditions on gas chromatography–mass spectrometry (GC–MS) profiling was investigated. Five EOs representing chemically diverse plant matrices, including Pistacia lentiscus (resin and stem) and leaf oils from Salvia rosmarinus, Laurus nobilis, and Thymus vulgaris, were analyzed using two capillary columns with different stationary phases: RTX-5MS (5% phenyl-substituted polysiloxane) and CP-Sil 5 CB (100% dimethylpolysiloxane). Comparative analysis revealed reproducible differences in chromatographic profiles and relative peak-area distribution, particularly within terpene-rich regions containing structurally related compounds. The most pronounced effects were observed for highly volatile monoterpenes, which were underrepresented under CP conditions. These findings demonstrate that chromatographic selectivity and column geometry may affect the semi-quantitative representation of EO profiles and contribute to variability in reported compositions. Overall, the results highlight the importance of carefully controlled analytical conditions in EO characterization.