Essential Oils from Six Aromatic Plants of Langtang National Park: Insights on Their Chemical Constituents via GC-MS Analysis

The essential oils were analyzed by GC-MS. The GC-MS analysis was performed on a Shimadzu GC-MS-QP2010 Plus available at the Instrument Section of the Department of Plant Resources. The capillary column used for the analysis was SH-RTX-5MS (60 m × 0.32 mm × 0.25 µm) with a crossbond of 5% diphenyl/95% dimethyl polysiloxane as the stationary phase. The GC analysis was performed under the following conditions: column oven temperature, 50 °C; injection temperature, 250 °C; ion source temperature, 250 °C; interface temperature, 200 °C; split injection mode with a split ratio of 80; Helium with a pressure of 53.8 kPa; total gas flow, 112.3 mL/min; column flow, 1.35 mL/min. The GC-MS system starts with an initial oven temperature of 50 °C for 1 min, then increases to 230 °C at a rate of 3 °C for 9 min. Mass spectral detection was carried out in electron ionization mode by scanning at 40 to 350 m/z. The total time required for analyzing a single sample was 70 min.
The chemical components of the essential oils were identified by comparing their mass spectral fragmentation patterns with those in the National Institute of Standard Technology Library (NIST) 2017 and Flavor and Fragrance Natural and Synthetic Compounds (FFNSC) 4.0 library and also by comparing the retention times of the components with those of the reference compounds. The percentage of each component (Area %) is reported as raw percentages based on the total ion chromatogram (TIC) without standardization.

The composition of essential oils obtained via hydrodistillation of leaves of Rhododendron anthopogon (AN), Artemisia dubia (AR), Boenninghausenia albiflora (BE), Elsholtzia fruticosa (EL), Juniperus recurva and Rhododendron setosum (SE) was determined by GC-MS. Figure 2Figure 3Figure 4Figure 5Figure 6 and Figure 7 show the TIC of the essential oils with peak numbers (A), extracted chromatograms of the prominent peaks with the names of the constituents (B, C), and the mass spectrum of the major constituent (C) of each essential oil. The composition of the essential oil (see the Supplementary Materials) as per the GC-MS analysis confirmed the presence of terpenoid components, mostly monoterpenes and sesquiterpenes.
Figure 2. TIC of essential oil from Rhododendron anthopogon (A), Inset: Extracted chromatogram from RT 12–20 min (B) and 32–42 min (C) and mass spectrum of Peak #2 (α–pinene) (D).
Figure 3. TIC of essential oil from Artemisia dubia (A), Inset: Extracted chromatogram from RT 11–20 min (B) and 35–44 min (C) and mass spectrum of Peak #1 (santolina-triene) (D).
Figure 4. TIC of essential oil from Boenninghausenia albiflora (A), Inset: Extracted chromatogram from RT 11–22 min (B) and 35–45 min (C) and mass spectrum of Peak #5 (β-myrcene) (D).
Figure 5. TIC of essential oil from Elsholtzia fruticosa (A), Inset: Extracted chromatogram from RT 12–26 min (B) and 35–40 min (C) and mass spectrum of Peak #11 (Perillene) (D).

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