*3.2. Extraction of EO, GC-MS Analysis, and Identification of Chemical Constituents*

About 250 g of the air-dried powder aerial parts of *P. lapathifolia* was subjected to hydrodistillation over Clevenger-type apparatus for three hours, and the dark yellow, oily layer was separated by n-hexane via a separating funnel. The EO chemical composition was analyzed and identified based on gas chromatography–mass spectrometry (GC–MS) using the instrument at the Medicinal and Aromatic Plants Research Dept., National Research Center, Egypt. The instrument comprises a TRACE GC Ultra Gas Chromatographs (THERMO Scientific Corp., Miami, CA, USA) and a thermo mass spectrometer detector (ISQ Single Quadrupole Mass Spectrometer; Model ISQ spectrometer, THERMO Scientific Corp., Miami, CA, USA). The system was equipped with a TR-5 MS column with specifications of 30 m × 0.32 mm i.d. and 0.25 μm film thickness. Helium was used as a carrier gas at a flow rate of 1.0 mL min−<sup>1</sup> and a split ratio of 1:10. The temperature program started at 60 ◦C for one minute and was then raised 4.0 ◦C every minute to 240 ◦C, then held for one minute. Electron ionization (EI) at 70 eV with a spectral range of *m*/*z* 40–450 was used for performing mass spectra. The chemical constituents of the EO were tentatively identified by their retention indices (relative to n-alkanes C8-C22) and mass spectrum matching to the Wiley spectral library collection and the NSIT library database [41].
