## 3 Results and Discussion
### Comparison of Different Extraction Methods
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{
\begin{tabular}{c} **Retention** \\ **Time (min)** \\ \end{tabular} } & \multirow{2}{*}{**Compounds**} & \multirow{2}{*}{**RI a**} & **CAS** & **Molecular** & \multicolumn{2}{c}{**Relative Area**} \\  & & & & **Number** & **Formula** & **Percentage (\%)** \\ \hline
1 & 7.334 & Dodecanal & 1408 & 112-54-9 & C\({}_{12}\)H\({}_{24}\)O & 7.10 & 6.52 \\
2 & 8.575 & Dihydro-\(\beta\)-ionone & 1434 & 17283-81-7 & C\({}_{13}\)H\({}_{22}\)O & 3.09 & 2.74 \\
3 & 8.761 & 4,6-Dimethyl-dodecane & 1437 & 61141-72-8 & C\({}_{14}\)H\({}_{30}\) & 6.49 & 5.78 \\
4 & 9.51 & Geranylacetone & 1454 & 3796-70-1 & C\({}_{13}\)H\({}_{22}\)O & 5.93 & 5.55 \\
5 & 9.875 & 1-Dodecanol & 1462 & 112-53-8 & C\({}_{12}\)H\({}_{26}\)O & 2.95 & 2.68 \\
6 & 10.184 & 4-Decalactone & 1468 & 706-14-9 & C\({}_{16}\)H\({}_{2}\)O & 3.52 & 3.26 \\
7 & 10.395 & Allyl \(n\)-decanoate & 1473 & 57856-81-2 & C\({}_{13}\)H\({}_{24}\)O\({}_{2}\) & nd b & 2.35 \\
8 & 10.645 & Trans-\(\beta\)-ionone & 1478 & 79-77-6 & C\({}_{13}\)H\({}_{20}\)O & 5.31 & 5.12 \\
9 & 11.156 & 2H-pyran-2-one & 1489 & 705-86-2 & C\({}_{10}\)H\({}_{18}\)O\({}_{2}\) & 2.49 & 2.28 \\
10 & 11.516 & 2-Tridecanone & 1496 & 593-08-8 & C\({}_{13}\)H\({}_{26}\)O & 6.29 & 5.97 \\
11 & 12.586 & Tridecanal & 1519 & 10486-19-8 & C\({}_{13}\)H\({}_{26}\)O & 4.24 & 3.74 \\
12 & 13.322 & 3,5,9-undecaterin-2-one & 1534 & 141-10-6 & C\({}_{13}\)H\({}_{20}\)O & 2.91 & 2.75 \\
13 & 14.334 & Nerololidol & 1556 & 7212-44-4 & C\({}_{15}\)H\({}_{26}\)O & 5.95 & 5.43 \\
14 & 14.767 & Dodecanoic acid & 1565 & 143-07-7 & C\({}_{12}\)H\({}_{24}\)O\({}_{2}\) & 3.92 & 3.57 \\
15 & 15.87 & Dodecanoic & 1588 & 106-33-2 & C\({}_{14}\)H\({}_{28}\)O\({}_{2}\) & 4.29 & 3.84 \\
16 & 18.691 & \(\beta\)-Acorenol & 1638 & 28400-11-5 & C\({}_{15}\)H\({}_{26}\)O & 3.02 & 2.86 \\
17 & 20.125 & Trans-Farnesol & 1662 & 106-28-5 & C\({}_{15}\)H\({}_{26}\)O & nd & 2.71 \\
18 & 20.304 & Ar-Turmerone & 1665 & 532-65-0 & C\({}_{16}\)H\({}_{20}\)O & 2.21 & 2.13 \\
19 & 20.548 & (E) 2-tetradecenal & 1669 & 51534-36-2 & C\({}_{14}\)H\({}_{26}\)O & 3.70 & 3.51 \\
20 & 21.035 & \(\gamma\)-dodecalactone & 1677 & 2305-5-7 & C\({}_{12}\)H\({}_{22}\)O\({}_{2}\) & nd & 1.83 \\
21 & 21.967 & 2-pentadecanone & 1693 & 2345-28-0 & C\({}_{15}\)H\({}_{30}\)O & 1.99 & 1.94 \\
22 & 22.499 & Pentadecane & 1702 & 1921-70-6 & C\({}_{19}\)H\({}_{40}\) & 5.41 & 4.81 \\
23 & 23.347 & Farnesol & 1716 & 4602-84-0 & C\({}_{15}\)H\({}_{26}\)O & 4.20 & 3.91 \\
24 & 24.057 & Methyl tetradecanoate & 1728 & 124-10-7 & C\({}_{15}\)H\({}_{20}\)O\({}_{2}\) & 2.52 & 2.39 \\
25 & 27.351 & Ethyl myristate & 1784 & 124-06-1 & C\({}_{16}\)H\({}_{23}\)O\({}_{2}\) & 2.51 & 2.44 \\  & & Total identified compounds & - & - & - & 90.03 & 90.11 \\ \hline \hline \end{tabular}  
* Retention indices relative to C\({}_{7}\)–C\({}_{40}\)\(n\)-alkanes on the HP-5 MS capillary column; b Not detected.  
\end{table} 
Table 3: Chemical composition of essential oils by GC-MS analysis. Most of the traditional methods require organic solvents, which resulting environmental pollution and potential health hazards to operators. On the contrary, ionic liquid is used as extraction solvent in our IL-UMASDE, ionic liquid vapor pressure is very low, so it can reduce the environmental pollution and health hazards to operators caused by solvent evaporation [22]. The ionic liquids are so expensive that its application was limited. Thus, the development of cheaper ionic liquids is the future research direction.