## 2 Results  
### Chemical Composition of Essential Oil  
The chemical complexity of the essential oil obtained by the HS-SPME of the dry plant powder aerial part was determined using GC-MS analysis and is tabulated in Table 1, Figure 1. Compounds are listed in the order of elution on the capillary column, with retention times (Rts). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**\#** & **Compound** & **Rt (min.)** & **RI** & **\%Conc.** \\ \hline
1 & Ethyl 2-methylbutyrate & 10.88 & 845.00 & 0.10 \\ \hline
2 & \(\alpha\)-Thujene & 14.71 & 931.00 & 0.10 \\ \hline
3 & \(\alpha\)-Pinene & 15.15 & 940.00 & 0.10 \\ \hline
4 & Camphene & 15.94 & 957.00 & 0.10 \\ \hline
5 & Benzaldehyde & 16.16 & 961.00 & 0.10 \\ \hline
6 & Sabinene & 17.00 & 979.00 & 0.10 \\ \hline
7 & \(\beta\)-Pinene & 17.30 & 985.00 & 0.10 \\ \hline
8 & 2-Octanone & 17.40 & 987.00 & 0.10 \\ \hline
9 & Myrcene & 17.58 & 991.00 & 0.10 \\ \hline
10 & Octan-2-ol & 17.85 & 996.00 & 0.10 \\ \hline
11 & \(\alpha\)-Phellandrene & 18.51 & 1010.00 & 0.10 \\ \hline
12 & \(\alpha\)-Terpinene & 19.11 & 1022.00 & 0.10 \\ \hline
13 & \(p\)-Cymene & 19.45 & 1029.00 & 0.20 \\ \hline
14 & Limonene & 19.73 & 1034.00 & 2.60 \\ \hline
15 & Artemisia ketone & 21.00 & 1060.00 & 1.60 \\ \hline
16 & \(\gamma\)-Terpinene & 21.17 & 1063.00 & 0.10 \\ \hline
17 & _cis_-sabinene hydrate & 21.61 & 1072.00 & 0.30 \\ \hline
18 & 2-Nonanone & 22.53 & 1090.00 & 20.00 \\ \hline
19 & Terpinen-4-ol & 22.70 & 1094.00 & 0.20 \\ \hline
20 & 2-Nonanol & 22.87 & 1097.00 & 1.50 \\ \hline
21 & Linalool & 22.97 & 1099.00 & 0.50 \\ \hline
22 & Nonanal & 23.10 & 1102.00 & 0.10 \\ \hline
23 & Oct-2-yl acetate & 24.69 & 1134.00 & 0.30 \\ \hline
24 & Geijerene & 25.59 & 1153.00 & 1.40 \\ \hline
25 & Camphor & 25.65 & 1154.00 & 2.70 \\ \hline
26 & Borneol & 26.70 & 1176.00 & 0.10 \\ \hline
27 & 2-Decanone & 27.43 & 1190.00 & 1.60 \\ \hline
28 & \(\alpha\)-Terpineol & 27.74 & 1197.00 & 0.10 \\ \hline
29 & _cis_-dihydroracurone & 28.02 & 1203.00 & 0.30 \\ \hline
30 & _trans_-dihydroracurone & 28.42 & 1211.00 & 0.60 \\ \hline
31 & 2-Nonyl acetate & 29.43 & 1233.00 & 7.50 \\ \hline
32 & Carvone & 30.24 & 1250.00 & 1.30 \\ \hline
33 & Isogeijerene C & 31.00 & 1266.00 & 0.10 \\ \hline
34 & 2-Undecanone & 32.33 & 1295.00 & 37.30 \\ \hline
35 & 2-Undecanol & 32.53 & 1299.00 & 0.70 \\ \hline
36 & 3-Nonyl acetate & 32.87 & 1306.00 & 0.10 \\ \hline
37 & 2-Decyl acetate & 33.94 & 1330.00 & 0.10 \\ \hline
38 & Piperitenone & 34.85 & 1351.00 & 0.10 \\ \hline
39 & 6-Dodecanone & 35.47 & 1365.00 & 1.20 \\ \hline
40 & (Z)-ethyl cinnamate & 36.09 & 1379.00 & 0.10 \\ \hline
41 & 8-epi-Dictamol & 36.48 & 1387.00 & 0.10 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of the _Ruta caldepensis_ aerial part essential oil extracted using HS-SPME. The application of headspace solid-phase microextraction (HS-SPME) to the aerial part of the Saudi chalepensis species resulted in 0.83% (_v/w_) yields of pale-yellow essential oil. The volatile constituents of the essential oil were identified by comparing their mass spectra to the NIST08 mass spectral database. The relative percentages of the individual components were calculated based on the GC/MS peak area. The GC/MS analysis of the _R. chalepensis_ oil revealed the presence of 68 aroma constituents with a total yield of 97.70%. This showed that this essential oil