## 3 Results and Discussion
### HS-SPME-GC-MS Analysis of Volatile Compounds
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Constituents** & **Class a** & **LRI b** & **RI Lit. c** & **\%** \\ \hline \(\alpha\)-pinene & MH & 941 & 939 & 1.0 \\ \(\beta\)-pinene & MH & 982 & 979 & 10.6 \\ \(\alpha\)-phellandrene & MH & 1006 & 1003 & 0.3 \\ p-cymene & MH & 1027 & 1025 & 5.0 \\ cis-sabinene hydrate & MO & 1070 & 1070 & 0.2 \\ nopinone & MO & 1139 & 1138 & 0.3 \\ trans-pinocarveol & MO & 1141 & 1140 & 2.3 \\ pinocarvone & MO & 1164 & 1164 & 1.5 \\
4-terpineol & MO & 1179 & 1177 & 0.2 \\ myrtenol & MO & 1195 & 1196 & 1.3 \\ verbenone & MO & 1207 & 1205 & 0.7 \\ methyl thymol & MO & 1234 & 1235 & 0.2 \\ (E)-anethole & PP & 1284 & 1284 & 0.5 \\ trans-pinocarylacetate & MO & 1298 & 1297 & 0.2 \\ theaspirane II & AC & 1315 & 1315 & 0.1 \\ myrtenyl acetate & MO & 1327 & 1327 & 0.7 \\ \(\delta\)-elemene & SH & 1340 & 1338 & 1.4 \\ \(\alpha\)-longipinene & SH & 1352 & 1353 & 0.5 \\ cylcosativene & SH & 1369 & 1368 & 0.6 \\ \(\alpha\)-ylangene & SH & 1372 & 1372 & 0.4 \\ \(\alpha\)-copane & SH & 1377 & 1376 & 1.2 \\ geranyl acetate & MO & 1383 & 1381 & 0.3 \\ \(\beta\)-elemene & SH & 1393 & 1391 & 2.6 \\ longifolene & SH & 1403 & 1402 & 0.1 \\ \(\alpha\)-gurjunene & SH & 1410 & 1409 & 0.3 \\ \(\beta\)-caryophyllene & SH & 1419 & 1419 & 9.2 \\ \(\beta\)-copane & SH & 1430 & 1431 & 0.3 \\ \(\gamma\)-elemene & SH & 1434 & 1433 & 0.6 \\ trans-\(\alpha\)-bergamotene & SH & 1437 & 1435 & 0.7 \\ epi-\(\beta\)-santalene & SH & 1449 & 1448 & 0.5 \\ \(\alpha\)-humulene & SH & 1456 & 1455 & 1.0 \\ alloaromodendrene & SH & 1462 & 1460 & 4.4 \\ \(\beta\)-chamigrene & SH & 1476 & 1475 & 16.2 \\ germacrene D & SH & 1481 & 1481 & 4.3 \\ \(\beta\)-seline & SH & 1486 & 1485 & 1.4 \\ \(\alpha\)-seline & SH & 1495 & 1494 & 12.8 \\ \(\alpha\)-muvolene & SH & 1499 & 1500 & 0.1 \\ trans-\(\gamma\)-cadinene & SH & 1514 & 1515 & 5.2 \\ \(\delta\)-cadinene & SH & 1524 & 1523 & 1.5 \\ \(\alpha\)-cadinene & SH & 1538 & 1539 & 0.2 \\ germacrene B & SH & 1557 & 1556 & 0.3 \\ (E)-nerolidol & SO & 1564 & 1564 & 0.3 \\ germacrene d-4-ol & SO & 1575 & 1576 & 1.4 \\ pathulenol & SO & 1577 & 1578 & 1.1 \\ carophyllene oxide & SO & 1582 & 1581 & 0.7 \\ geranyl l-methylbutyrate & MO & 1600 & 1596 & 0.4 \\ \(\gamma\)-eudesmol & SO & 1632 & 1632 & 0.4 \\ \(\tau\)-cadinol & SO & 1641 & 1640 & 2.6 \\ \hline Monoterpene hydrocarbons & & & & 16.9 \\ Oxygenated monoterpenes & & & & 8.3 \\ Sesuiterence hydrocarbons & & & & 65.8 \\ Oxygenated sesquiterpenes & & & & 6.5 \\ Phenylpropanoids & & & & 0.5 \\ Apocarotonoids & & & & 0.1 \\ Total identified & & & & 98.1 \\ \hline \hline \end{tabular}  
* MH: monoterpene hydrocarbons; MO: oxygenated monoterpens; SH: sesquiterpene hydrocarbons; SO: oxygenated sesquiterpenes; PP: phenylpropanoids; AC: apocarotonoids. b Linear retention index on HP-SMS column, experimentally determined using homologous series of C\({}_{8}\)–C\({}_{32}\) alkanes. c Linear retention index taken from the NIST library.  
\end{table} 
Table 1: Aroma profile (relative percentages of identified compounds) of the aerial parts of _P. spinosa_ obtained using HS-SPME–GC–MS. Compounds are listed in order of their elution from an HP-5 MS column. was dominated by a mixture of oxygenated sesquiterpenes (61.12%) and sesquiterpene hydrocarbons (34.76%). Moreover, the main constituents were different \(\alpha\)-cadinol (16.48%), germacra-1(10),5-diene-3,4-diol (14.45%), \(\gamma\)-cadinene (12.03%), and \(\alpha\)-muurolol (9.89%) were the most abundant ones, while, except for \(\gamma\)-cadinene, they were not detected in our study. Nevertheless, the results from the analysis of HS-SPME fractions and EOs obtained by hydro-distillation are not directly comparable due to the completely different sampling methods. For instance, the low temperature maintained during the HS-SPME sampling avoids the thermal degradation of some constituents, conversely to distillation methods. This aspect can partially justify why many of the major constituents identified by [PERSON] et al. (2010) were not found in our extract or were present in low amounts.