3.4. Gas Liquid Chromatography-Mass Spectrometry (GLC/MS)

The composition of the essential oils was determined using a GLC-MS system (Agilent Technologies, Middelburg, The Netherlands) outfitted with a gas chromatograph (7890B), mass spectrometer detector (5977A), and HP-5MS column (30 m × 0.25 mm internal diameter and 0.25 μm film thickness) at Central Laboratories Network, National Research Centre, Cairo, Egypt. The temperature program was set to 40 °C for 1 min; then raised at 4 °C/min to 150 °C for 6 min; and lastly raised at 4 °C/min to 210 °C and held for 1 min. The injector and detector were both kept at 280 °C and 220 °C, respectively. Electron ionization (EI) at 70 eV was used to obtain the mass spectra with a spectral range of m/z 50–550 and a solvent delay of 5 min. The samples were diluted with n-hexane (≥99%, Sigma–Aldrich, Sternheim, Germany, 1:19, v/v) injected at 1 µL volume, and analyses were carried out using hydrogen as the carrier gas at a flow rate of 1.0 mL/min. The retention indices were calculated based on the retention times of the standard alkane series (C7–C40, Sigma Aldrich GmbH, Sternheim, Germany). The recording and integrating of the chromatograms was performed using enhanced Chem Station software, version MSD F.01.01.2317 (Agilent Technologies, Middelburg, The Netherlands). Based on the normalization method using the reading of three chromatographic runs, quantitation was carried out. The identification of the compounds was elucidated by comparing their retention indices (RIs) and mass spectral data with the reported data in the Wiley Registry of Mass Spectral Data (9th Ed.), NIST Mass Spectral Library (2011).