## 3 Materials and Methods
### GC-MS Analysis  
Approximately 20 mg of rose essential oil was extracted from 100 g of the flower sample and dissolved in 1 mL of N-hexane for four hours. For each sample, three replicates were used. As described by [PERSON] et al. [37], essential oil samples were dissolved in dichloromethane for GC-MS analysis. GC-MS analysis was performed using a Thermo Scientific Trace GC Ultra/ISQ Single-Quadrupole MS with a TG-5 MS fused-silica capillary column (30 m, 0.251 mm, 0.1 mm film thickness) Markham, ON, CA. Owing to the simplicity and rapidity of this method, it is possible to accurately identify the origin of rose varieties. Table 1 lists the parameters used in this analysis.  
After headspace injection, the volatile organic components in the rose samples were detected quickly by heating them directly. By analyzing the gas-phase ion migration spectra and fingerprint chromatograms, the instrument can determine the differences between the volatile organic compounds in each sample. Based on the percentage of the relative peak area, all identified components were quantified. The compounds were tentatively identified based on a comparison of their relative retention times and mass spectra with NIST and Wiley library data obtained from the GC-MS system [38]. An example of GC-MS analysis that we received from the laboratory is provided in Figure 2 and Table 2.  
Figure 1: Geographical locations of the 10 Taif rose farms (Al-Hada (**a**) and Al-Shafa (**b**)) from which the samples were collected.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter Settings for Thermo Scientific, Trace GC Ultra/ISQ Single-Quadrupole MS** \\ \hline Analysis time & 60 min. \\ Column type & TG-SMS fused-silica capillary column \\ Ionization energy & 70 eV \\ Carrier drift gas & Helium (He) \\ Carrier gas flow rate & 1 mL/min. \\ Initial MS temperature 40 \({}^{\circ}\)C/3 min & 40 \({}^{\circ}\)C \\ Increasing rate of temperature & 5 \({}^{\circ}\)C/min (hold 5 min) \\ The injector and MS final temperature & 280 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table}
Table 1: Various parameters of GC–MS analysis used in this research.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**R\({}_{\bf T}\)** & **Mw** & **MF** & **Area\%** & **Compound Name** \\ \hline
5.16 & 232 & C14H16O 3 & 0.83 & Ethyl- 2-[(benzyloxymethyl)methyl]cycloprop-2-ene-1-carboxylate \\ \hline
6.46 & 210 & C15H30 & 1.05 & 2,4,6,8-Tetramethyl-1-undecene \\ \hline
8.11 & 136 & C10H16 & 18.43 & \(\hat{\rm a}\)-Pinene \\ \hline
8.29 & 136 & C\({}_{9}\)H\({}_{12}\)O & 1.06 & Spiro[cyclopropane-1,6[3]-oxatricyclool [3.2.1.0(2,4)]octane] \\ \hline
9.41 & 120 & C 9H12 & 4.09 & 1,8-Nonadiyne (CAS) \\ \hline
9.56 & 136 & C10H16 & 0.48 & Sabinene \\ \hline
10.02 & 108 & C8H12 & 8.42 & 3-Cyclopentyl-1-propyne -6 \\ \hline
10.13 & 100 & C\({}_{6}\)H\({}_{12}\)O & 0.23 & Cyclopentamenethanol \\ \hline
10.68 & 136 & C10H16 & 0.64 & \(\varsigma\)Terpinene \\ \hline
10.95 & 134 & C10H14 & 0.55 & Benzene,1-ethyl-2,4-dimethyl (CAS) \\ \hline
11.07 & 136 & C10H16 & 1.65 & \(\hat{\rm a}\)-Phellandrene \\ \hline \hline \end{tabular}
\end{table}
Table 2: Example of GC–MS data of rose oil composition. RT = retention time, MW = molecular weight, MF = molecular formula. Area% = the percentage of the component.  
Figure 2: Representative sample of the GC-MS fingerprints generated by GC-MS analysis of the studied rose oils.