N alkane

The essential oils were analyzed using GC–FID and GC–MS. The analysis was conducted using an Agilent 7990 B gas chromatograph equipped with a 5988A mass spectrometer and a HP-5MS (0.25 mm i.d., 30 mL, 0.25 μm f.t., 5% phenyl methyl polysiloxane). The following oven temperature was used: 5 min at 60 °C, then up to 240 °C with the rate of 3 °C min⁻¹, held for 10 min. Helium (carrier gas) flow rate was 1 mL min⁻¹; the injector split ratio was 1:30; the mass range and electron impact (EI) were 400 m/z and 70 eV, respectively. The identification of constituents was performed using the procedure explained by Morshedloo et al.^{60 (link)}, which is based on the interactive combination of linear retention indices (RIs), calculated respect to a homologous series of n-alkanes (Supelco, Bellefonte, CA), and the mass spectrum (MS) matching with commercial libraries (ADAMS, WILEY 275 and NIST 17). GC-FID analysis was performed using an Agilent 7990 B gas chromatograph equipped with a flame ionization detector (FID), capillary column VF 5MS (30 mL, 0.25 mm i.d., 0.50 μm f.t., 5% phenyl methyl polysiloxane). The same oven temperature reported for GC–MS was used. The injection volume of the essential oil was 1 μL the essential oil in n-hexane (1:100). Quantification of the constituents was performed by peak area normalization without using correction factors^{61 (link)}.

An Agilent 6890/5975C GC‐MS system equipped with HP‐5 ms column (30 m × 0.25 mm i.d., 0.25 μm film thickness; J&W Scientific) was used to analyze volatile compounds that accumulated on the SPME fiber. The carrier gas was helium with splitless mode, which was delivered at a linear velocity of 1 ml/min. The desorption time was 5 min in the injection port at 250°C. The temperature was programmed to be hold at 35°C for 3 min and increased to 280°C at a rate of 5°C/min. The mass selective detector was operated in the electron impact ionization mode at 70 eV, in the scan range m/z 40–400. The interface temperature was 230°C, and the retention time of each volatile was converted to the Kovats retention index using n‐alkanes (Sigma, Co.) as references. The volatile compounds were tentatively identified by matching the mass spectra with the spectra of the reference compounds in both the Wiley mass spectra (MS) library (8th edn) and the NIST/EPA/NIH MS library (version 2.2a) and verified on the basis of mass spectra obtained from the literature and comparison of Kovats retention indices with those reported in the literature. Finally, identification accuracy was determined by separating relevant standard compounds through GC‐MS analysis under the same conditions (Dong et al., 2013).