**2.3 Method for chemical analysis**

There is a myriad of technics and methods for essential oil chemical profiling. All the methods used in organic chemistry can be used here. Due to their volatility nature, the compounds that constitute essential oil are preferably analyzed by gas chromatography (GC). Gas chromatography alone does not provide enough data for good chemical proofing. Therefore, many other analytical tools have been used such as mass spectrometry (MS), infrared spectroscopy (IR), and nuclear magnetic resonance (NMR). As well, many technics have been used to make the GC a better tool for chemical profiling, and these include chiral selective GC and multidimensional GC. Advances in liquid chromatography have highlighted the usefulness of high-pressure liquid chromatography (HPLC) as a tool for essential oil analysis. Many variants are available to date as multidimensional HPLC, HPLC-MS, and HPLC-GC. The following section will walk you through gas chromatography and gas chromatography coupled with mass spectrometry for their popularity and the Fourier transform infrared spectroscopy for its simplicity and for being environment-friendly and long-term cost-effectiveness.

**19**

index.

*Essential Oil's Chemical Composition and Pharmacological Properties*

*2.3.1 Gas chromatography and variant in essential oil analysis*

Gas chromatography is an old essential oil chemical profiling method. As all the chromatographic methods, it is based on the single compound separation from a complex matrix between two phases regarding their affinity between the phases, their shape, and mass. The mobile phase is the one which moves by capillarity or pressure transporting compounds faster or slower toward the fixed phase. In GC, the mobile phase is a gas and the fixed phase is a solid at room temperature, but at a high temperature, this phase will be slightly melted but will remain fixed on the column. For analysis, the essential oil is mixed with a solvent (mostly hexane or pentane) and introduced into the injector room set at 200°C with the help of a syringe. The mixture is carried by the mobile phase into the column. Here the temperature drops down to about 50°C. All the compounds settle down at different distance in the column. This column itself is placed in an oven set with gradient increasing temperature (1–5°C/min). Each compound has it vaporization point and therefore when the oven temperature will reach this point, it will be volatilized thereby take off from the stationary (fixed) phase and carry and spit off out of the column.

Usually, the column is connected to a detector, which in the case of essential oil analysis is the flame ionization detector (FID). In this case, when the compound comes out of the column, it is burned and the increasing temperature in the flame, proportional to the compound scaffold, is detected and transformed into a peak. The compound identification is done by using the retention time and/or the Kovats index. The following formula as presented in Adams is used to calculate the Kovats

*KI*(*x*) <sup>=</sup> <sup>100</sup>*Pz* <sup>+</sup> <sup>100</sup>( *logRTx* <sup>−</sup> *logRTPz* \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *logRTPz* <sup>−</sup> *logRTPz*+1) (1)

*KI*(x) is the Kovats indices of compounds *x*, *P*(*z*) is the paraffin with *z* carbon atoms, *P*(*z* + 1) is the paraffin with *z* + 1 carbon atom, and *RT* is the retention time.

*AI*(*x*) is the arithmetic index of compounds *x*, *P*(*z*) is the paraffin with *z* carbon atom, *P*(*z* + 1) is the paraffin with the *z* + 1 carbon atom, and *RT* is the retention time. After calculation of index, the value is compared with that of the online libraries

When the GC is connected to MS, the compound is accelerated and ionized into

**Table 1** summarizes few retention or Kovats indexes reported in the literature for randomly selected plant and randomly selected papers. The diversity of chemotype obtained per essential oil is interesting. But the question about the accuracy of this profiling method has come up. Moreover, the Internet-based data bank proposes a huge range of retention indexes for the same compounds. For illustration mater, let us take the eucalyptol also called cineol-1,8. In the NIST database in the slightly polar column, here dimethyl-silicone with 5% phenyl group (DIMS 5P), this compound have a retention indexes ranging from 1021 to 1044 [44]. This range represents 23 units in the retention indexes. Taking into consideration the Kovats or Van Den Dool and Kartz formula, this range (8 min 57 s to 9 min 44 s) represents a gap of 47 s. For the same column, in terms of polarity, in Adams Database, during this period, 24 single compounds can be identified [45]. More complexly, there are overlappings in

\_\_\_\_\_\_\_\_\_\_\_ *RTx* − *RTPz*

*RTPz* <sup>−</sup> *RTPz*+1) (2)

The linearization of this formula presented in Adams is as follows:

the different compartment of its scaffold and detected as bands.

*AI*(*x*) = 100*Pz* + 100(

or the Adams library [45].

*DOI: http://dx.doi.org/10.5772/intechopen.86573*

*Essential Oil's Chemical Composition and Pharmacological Properties DOI: http://dx.doi.org/10.5772/intechopen.86573*

*Essential Oils - Oils of Nature*

*2.2.5 Solvent extraction*

*2.2.6 Supercritical fluid extraction*

this method is the complexity of the system.

**2.3 Method for chemical analysis**

absolute.

hours by heating. The aromatized wax is then called concrete. This later undergoes solubilization in a polar solvent and then partitioned with absolute ethanol. The product obtained after this process is at most a part of the essential oil as present in plant, and it contains many other terpenes that can be solubilized in fats used; that is, while at the end, the product is not called essential oil but

This is the oldest method for obtaining crude extract from plants. The principle is based on the solubilization of the compounds in the cells by the solvent. This method also has two variants as it can be run in room temperature or in high temperature. But no matter whether the extraction was performed in room temperature or not, the solvent will be separated by Rotavapor regarding the volatility of the solvent. This method does not really lead to obtaining the essential oil as all the nonvolatile compounds are also extracted by this approach. Therefore, the chemical profile will not be that of the volatile fraction of the plants but for

This method is the most modern and sophisticated. It uses gases at their supercritical stage. The gas at supercritical stage is liquid due to the high pressure applied to it. Many solvents can be used as the method brings the solvent at its temperature and pressure above its thermodynamic critical point, but the most used is CO2 for the reason that it needs less pressure to be liquified, it is less reactive than other, it is noninflammable, it is nontoxic and available at low cost with high purity, and most importantly it can be removed from the plant material using just the press release. This method is based on the fact that gas at the supercritical state can enter throughout the plant material like a gas and dissolve component like a liquid. After the extraction procedure, the essential oils compounds are mixed with the supercritical fluid (in liquid form). The separation is performed by reducing temperature and increasing the pressure up to room conditions [13–17]. The principal limit of

There is a myriad of technics and methods for essential oil chemical profiling. All the methods used in organic chemistry can be used here. Due to their volatility nature, the compounds that constitute essential oil are preferably analyzed by gas chromatography (GC). Gas chromatography alone does not provide enough data for good chemical proofing. Therefore, many other analytical tools have been used such as mass spectrometry (MS), infrared spectroscopy (IR), and nuclear magnetic resonance (NMR). As well, many technics have been used to make the GC a better tool for chemical profiling, and these include chiral selective GC and multidimensional GC. Advances in liquid chromatography have highlighted the usefulness of high-pressure liquid chromatography (HPLC) as a tool for essential oil analysis. Many variants are available to date as multidimensional HPLC, HPLC-MS, and HPLC-GC. The following section will walk you through gas chromatography and gas chromatography coupled with mass spectrometry for their popularity and the Fourier transform infrared spectroscopy for its simplicity and for being environment-friendly and long-term

the compound that is soluble in the solvent used in the process [13–17].

**18**

cost-effectiveness.

#### *2.3.1 Gas chromatography and variant in essential oil analysis*

Gas chromatography is an old essential oil chemical profiling method. As all the chromatographic methods, it is based on the single compound separation from a complex matrix between two phases regarding their affinity between the phases, their shape, and mass. The mobile phase is the one which moves by capillarity or pressure transporting compounds faster or slower toward the fixed phase. In GC, the mobile phase is a gas and the fixed phase is a solid at room temperature, but at a high temperature, this phase will be slightly melted but will remain fixed on the column.

For analysis, the essential oil is mixed with a solvent (mostly hexane or pentane) and introduced into the injector room set at 200°C with the help of a syringe. The mixture is carried by the mobile phase into the column. Here the temperature drops down to about 50°C. All the compounds settle down at different distance in the column. This column itself is placed in an oven set with gradient increasing temperature (1–5°C/min). Each compound has it vaporization point and therefore when the oven temperature will reach this point, it will be volatilized thereby take off from the stationary (fixed) phase and carry and spit off out of the column.

Usually, the column is connected to a detector, which in the case of essential oil analysis is the flame ionization detector (FID). In this case, when the compound comes out of the column, it is burned and the increasing temperature in the flame, proportional to the compound scaffold, is detected and transformed into a peak. The compound identification is done by using the retention time and/or the Kovats index. The following formula as presented in Adams is used to calculate the Kovats index.

$$\begin{aligned} \text{(\dots} \\ \text{KI}\_{\langle x \rangle} = \mathbf{100}P\_x + \mathbf{100} \left( \frac{\log \text{RT}\_x - \log \text{RT}\_x}{\log \text{RT}\_x - \log \text{RT}\_{x\*1}} \right) \end{aligned} \tag{1}$$

*KI*(x) is the Kovats indices of compounds *x*, *P*(*z*) is the paraffin with *z* carbon atoms, *P*(*z* + 1) is the paraffin with *z* + 1 carbon atom, and *RT* is the retention time.

The linearization of this formula presented in Adams is as follows:

$$AI\_{(x)} = \mathbf{100} \, P\_x + \mathbf{100} \left( \frac{RT\_x - RTP\_x}{RTP\_x - RTP\_{x+1}} \right) \tag{2}$$

*AI*(*x*) is the arithmetic index of compounds *x*, *P*(*z*) is the paraffin with *z* carbon atom, *P*(*z* + 1) is the paraffin with the *z* + 1 carbon atom, and *RT* is the retention time.

After calculation of index, the value is compared with that of the online libraries or the Adams library [45].

When the GC is connected to MS, the compound is accelerated and ionized into the different compartment of its scaffold and detected as bands.

**Table 1** summarizes few retention or Kovats indexes reported in the literature for randomly selected plant and randomly selected papers. The diversity of chemotype obtained per essential oil is interesting. But the question about the accuracy of this profiling method has come up. Moreover, the Internet-based data bank proposes a huge range of retention indexes for the same compounds. For illustration mater, let us take the eucalyptol also called cineol-1,8. In the NIST database in the slightly polar column, here dimethyl-silicone with 5% phenyl group (DIMS 5P), this compound have a retention indexes ranging from 1021 to 1044 [44]. This range represents 23 units in the retention indexes. Taking into consideration the Kovats or Van Den Dool and Kartz formula, this range (8 min 57 s to 9 min 44 s) represents a gap of 47 s. For the same column, in terms of polarity, in Adams Database, during this period, 24 single compounds can be identified [45]. More complexly, there are overlappings in


**21**

*Essential Oil's Chemical Composition and Pharmacological Properties*

Compounds AP SAPC PC [6] [7] [8] [10] [93] a-Pinene 924–951 921–944 1008–1039 931 936 1075 961 939 Myrcene 975–991 980–995 1140–1175 980 991 1174 991 991 Camphene 936–965 936–959 1043–1086 944 952 1102 943 954 Eucalyptol 1013–1039 1021–1044 1186–1231 1021 1031 1221 1032 1031 Camphor 1106–1153 1127–1155 1481–1537 1122 1148 1547 1088 1144 Verbenone 1167–1198 1190–1224 1696–1735 1183 1209 — 1119 1207 Bornyl acetate 1259–1209 1264–1297 1549–1597 1272 1292 1612 1277 —

Compounds AP SAPC PC [89] [36] [9] [94] [95] Myrcene 975–991 980–995 1140–1175 981 988 — 980 992 a-Thujone 1076–1104 1099–1117 1385–1441 1104 1101 1105 — 1102 Camphor 1106–1153 1127–1155 1481–1537 1122 1141 1143 1108 1142 Eucalyptol 1013–1039 1021–1044 1186–1231 1027 1026 1034 1191 1032 b-Caryophyllene 1400–1442 1405–1440 1569–1632 1395 1417 1418 — 1418 Humulene 1439–1459 1436–1456 1637–1689 1430 1452 — 1430 1454 Viridiflorol 1561–1598 1569–1604 2041–2110 — — — 1587 —

Compounds AP SAPC PC [96] [97] [98] [99] [89] Eugenol 1323–1372 1345–1375 2100–2198 1392 1353 1370 1354 2098 b-Caryophyllene 14,000–1442 1405–1440 1569–1632 1458 1428 1426 1421 — Eugenyl acetate 1472–1493 1514–1531 2252–2277 1552 1538 — 1522 2107 Humulene 1439–1459 1436–1456 1637–1689 1579 — 1460 1455 —

Compounds AP SAPC PC [22] [100] [23] [98] [101] a-Terpinene 1001–1024 1007–1026 1154–1195 — 1010 1016 1019 1019 p-Cymene 1004–1029 1011–1033 1246–1291 1029 1014 1024 1026 1033 Limonene 1012–1038 1019–1039 1178–1219 — 1022 1028 1031 — Terpineol 1148–1180 1178–1230 1655–1687 — 1162 1194 1190 1177 g-Terpinene 1035–1062 1049–1069 1222–1266 1064 1049 1057 1062 1060 Linalool 1074–1098 1088–1109 1507–1564 — 1084 1099 1100 1107 Thymol 1260–1289 1272–1304 2100–2205 — — 1288 1296 1315 Carvacrol 1272–1300 1291–1344 2140–2246 1308 1286 1296 1305 b-Caryophyllene 14,000–1442 1405–1440 1569–1632 — — 1419 1419 1423

Compounds APC SPC PC [102] [103] [104] [105] [106] a-Pinene 1001–1024 1007–1026 1154–1195 939 — 926 943 935 Camphene 936–965 936–959 1043–1086 953 — 944 954 950 Linalool 1074–1098 1088–1109 1507–1564 — 1112 — — 1103

*DOI: http://dx.doi.org/10.5772/intechopen.86573*

**Retention indexes** *Rosmarinus officinalis*

*Saliva officinale*

*Syzygium aromaticum*

*Thymus vulgaris*

*Zingiber officinale*


*Essential Oils - Oils of Nature*

Compounds AP SAPC PC [26] [25] [24] [85] [86] Diallyl sulfide 835–872 831–872 1118–1177 855 784 — 846 854

Diallyl disulfide 1054–1078 1048–1095 1436–1526 1080 1111 1085 1079 1084

Diallyl trisulfide 1266–1292 1277–1320 1775–1822 1301 1207 1311 1301 1305

Compounds AP SAPC PC [5] [28] [29] [30] [14] Ocimene 1027–1050 1028–1047 1211–1251 1030 — 1043 — 1043 Linalool 1074–1098 1088–1109 1507–1564 1092 — 1107 1100 1101 Terpineol 1148–1180 1178–1203 1655–1687 1167 1179 — — 1181 Linalyl acetate 1234–1254 1238–1268 1532–1570 1246 — 1256 — 1258 Borneol 1134–1172 1152–1177 1653–1717 1155 1167 1170 1144 1169

Compounds AP SAPC PC [4] [13] [16] [12] [33] Neral 1211–1240 1231–1269 1641–1706 — — 1246 1245 1240 Nerol 1206–1239 1216–1250 1752–1832 — — 1228 — — Geranial 1236–1260 1252–1291 1680–1750 — — 1278 1271 1270 Geraniol 1231–1256 1238–1269 1795–1865 1185 1252 1258 — — Caryophyllene 1400–1442 1405–1440 1569–1632 — 1417 1405 1421 1418 Germacrene D 1458–1491 1446–1493 1676–1726 — 1484 1480 1489 1480 Cadinene 1506–1542 1503–1541 1734–1803 — 1523 1538 1514 —

Compounds AP SAPC PC [87] [88] [89] [90] [17] Eucalyptol 1013–1039 1021–1044 1186–1231 1031 1031 1027 1029 1026 Ocimene 1027–1050 1028–1047 1211–1251 1038 1045 — 1048 1034 Linalool 1074–1098 1088–1109 1507–1564 1111 1120 1085 1116 1095 Eugenol 1323–1372 1345–1375 2100–2198 — — 1377 1376 1330 Humulene 1439–1459 1436–1456 1637–1689 1447 1455 1430 1459 1445 Cadinene 1506–1542 1503–1541 1734–1803 1519 — 1497 — 1505

Compounds AP SAPC PC [3] [89] [91] [92] [15] a-Pinene 924–951 921–944 1008–1039 938 930 931 931 939 b-Phellandrene 1005–1036 995–1013 1148–1186 1040 978 1024 1021 1003 g-Terpinene 1035–1062 1049–1069 1222–1266 — 1049 1051 1050 1060 a-Cubebene 1345–1359 1438–1480 1438–1480 1357 — 1377 1352 1351 Farnesene 1484–1509 1488–1493 1627–1668 1455 1518 1453 1445 1443 b-Caryophyllene 14,000–1442 1405–1440 1569–1632 1437 1395 1419 1419 1419

891–915 887–928 1241–1322 916 918 — 908 915

1100–1132 1123–1165 1587–1605 1138 1116 1145 1126 1131

**Retention indexes** *Allium sativum*

Allyl methyl disulfide

Allyl methyl trisulfide

*Lavandula angustifolia*

*Melissa officinalis*

*Ocimum basilicum*

*Peper nigrum*

**20**


**Table 1.**

*Retention indexes of important compounds from 10 randomly selected essential oils.*

the range proposed by the NIST as reported by Babushok [44] as it can be observed in **Table 1**; for the same DIMS5P column, α pinene (921–944) is overlapping with camphene (936–959) and eucalyptol (1021–1044) is overlapping with ocimene (1028–1047) and camphor (1127–1155). These observations are the real pitfalls of these identification approaches and can lead to misuses of the valuable data from those data banks. In fact, these overlappings lead to compound identification oriented to the chemotype available in the literature rather than the real chemotype that is analyzed. And the previous paragraph had highlighted that the chemical profile thereby the pharmacological profile can change because of a myriad of factors. All these lead to questioning the robustness of this actual gold essential oil chemical profiling strategy not in the view of the provided database or analytic tools but in the view of data interpretation by the users.

#### *2.3.2 Infrared spectroscopy and chemometric analysis*

The idea besides the spectroscopy analysis is the fact that, in the electromagnetic radiation, there is a range of a tiny part of visible light that exists as a wave. This light moves in a straight line if the part of this light is not reflected, refracted, or absorbed by the matter. In biology and chemistry, this technique is used to produce an infrared spectrum in the case of infrared spectroscopy by passing an infrared radiation through a given sample knowing that the atom constituting the sample will lead to absorption of a part of the light energy. When a part of the molecule present in the sample absorbs this energy, it will become unstable and will react by twisting, stretching, bending, rocking, wagging, or scissoring depending on the bond linking these atoms with the rest of the molecule. The energy absorbed, the different reactions of the atom lead to the appearance of a specific peak on the spectrum [46–49].

The spectrum can be at least qualitatively interpreted without prior or additional chemometric algorithm as it provides a high level of specific information on the molecular aspect of the essential oil [50]. In fact, the spectrum regions are known and correspond to established characteristic group absorbances [47] and therefore the assignment can lead to specific chemical identification (**Figure 3**). But this is when the sample is a single compound. When the mixture is analyzed, the peak cannot be simply attributed to the compounds as it is most of the time the result of the overlapping small vibration of different closely related groups from a different molecule in the mixture.

For the quality purpose, the fingerprint region is most important. In fact, the fingerprint region is a unique vibrational signature that a given essential oil can have. It is as specific as the fingerprint is specific to a human. But to be more

**23**

**Figure 3.**

**Figure 4.**

*spectrum [51].*

*Essential Oil's Chemical Composition and Pharmacological Properties*

efficient in the analysis of the area, chemometric tool should be used such as derivation. This approach is a simple application of the derivate formula to the equation of the fingerprint region or a given region. This technique provides with key benefits. In fact, it enhances the resolution for the first derivative and the second derivative gives negative peaks of each band in the examined region [47] an example from **Figure 3** is given in **Figure 4A**. It is also possible to apply other data processing such

*Spectral processing of fingerprint (a), C-H (b) and O-H (c) regions of Ocimum basilicum essential oil's FTIR* 

*Infrared spectrum of Ocimum basilicum essential oil obtained from Fourier transform infrared spectroscopy.*

Using this approach, an increasing number of authors have succeeded in discriminating the essential oil of various plants based on their chemotype [46, 51–56]. Those authors have suggested that for a known essential oil, the fingerprint of the

This part of the chapter is huge and covers various aspects of human and animal care. It will be easier to find a disease that no essential oil as a whole or its component can exert any effect. Essential oils are used to manage even diseases that are not scientifically measurable these days. These include protecting against misfortune and bad spirit and protecting the soul after death. This aspect of the therapeutic use of the essential oil will not be described here. The following paragraphs will be

as baseline correction, smoothing, or curve fitting [47].

**3. Pharmacological property of essential oils**

oil should be used as a tool for rapid essential oil quality control.

*DOI: http://dx.doi.org/10.5772/intechopen.86573*

*Essential Oil's Chemical Composition and Pharmacological Properties DOI: http://dx.doi.org/10.5772/intechopen.86573*

#### **Figure 3.**

*Essential Oils - Oils of Nature*

**Retention indexes**

**Table 1.**

view of data interpretation by the users.

*2.3.2 Infrared spectroscopy and chemometric analysis*

*APC, apolar column; SPC, slightly polar column; PC, polar column.*

*Retention indexes of important compounds from 10 randomly selected essential oils.*

the range proposed by the NIST as reported by Babushok [44] as it can be observed in **Table 1**; for the same DIMS5P column, α pinene (921–944) is overlapping with camphene (936–959) and eucalyptol (1021–1044) is overlapping with ocimene (1028–1047) and camphor (1127–1155). These observations are the real pitfalls of these identification approaches and can lead to misuses of the valuable data from those data banks. In fact, these overlappings lead to compound identification oriented to the chemotype available in the literature rather than the real chemotype that is analyzed. And the previous paragraph had highlighted that the chemical profile thereby the pharmacological profile can change because of a myriad of factors. All these lead to questioning the robustness of this actual gold essential oil chemical profiling strategy not in the view of the provided database or analytic tools but in the

Eucalyptol 1323–1372 1345–1375 2100–2198 1033 1060 1015 1027 1032 Neral 1211–1240 1231–1269 1641–1706 — 1265 1249 1227 1247 Geranial 1236–1260 1252–1291 1680–1750 — 1292 — 1252 1379 Germacrene D 1458–1491 1446–1493 1676–1726 1481 1532 — 1469 b-Farnesene 14,000–1442 1405–1440 1569–1632 — 1518 — — 1458 Zingiberene 1463–1494 1485–1509 1696–1743 1495 1521 1492 1487 1508

The idea besides the spectroscopy analysis is the fact that, in the electromagnetic

The spectrum can be at least qualitatively interpreted without prior or additional

chemometric algorithm as it provides a high level of specific information on the molecular aspect of the essential oil [50]. In fact, the spectrum regions are known and correspond to established characteristic group absorbances [47] and therefore the assignment can lead to specific chemical identification (**Figure 3**). But this is when the sample is a single compound. When the mixture is analyzed, the peak cannot be simply attributed to the compounds as it is most of the time the result of the overlapping small vibration of different closely related groups from a different

For the quality purpose, the fingerprint region is most important. In fact, the fingerprint region is a unique vibrational signature that a given essential oil can have. It is as specific as the fingerprint is specific to a human. But to be more

radiation, there is a range of a tiny part of visible light that exists as a wave. This light moves in a straight line if the part of this light is not reflected, refracted, or absorbed by the matter. In biology and chemistry, this technique is used to produce an infrared spectrum in the case of infrared spectroscopy by passing an infrared radiation through a given sample knowing that the atom constituting the sample will lead to absorption of a part of the light energy. When a part of the molecule present in the sample absorbs this energy, it will become unstable and will react by twisting, stretching, bending, rocking, wagging, or scissoring depending on the bond linking these atoms with the rest of the molecule. The energy absorbed, the different reactions of the atom lead to the appearance of a specific peak on the

**22**

spectrum [46–49].

molecule in the mixture.

*Infrared spectrum of Ocimum basilicum essential oil obtained from Fourier transform infrared spectroscopy.*

#### **Figure 4.**

*Spectral processing of fingerprint (a), C-H (b) and O-H (c) regions of Ocimum basilicum essential oil's FTIR spectrum [51].*

efficient in the analysis of the area, chemometric tool should be used such as derivation. This approach is a simple application of the derivate formula to the equation of the fingerprint region or a given region. This technique provides with key benefits. In fact, it enhances the resolution for the first derivative and the second derivative gives negative peaks of each band in the examined region [47] an example from **Figure 3** is given in **Figure 4A**. It is also possible to apply other data processing such as baseline correction, smoothing, or curve fitting [47].

Using this approach, an increasing number of authors have succeeded in discriminating the essential oil of various plants based on their chemotype [46, 51–56]. Those authors have suggested that for a known essential oil, the fingerprint of the oil should be used as a tool for rapid essential oil quality control.

### **3. Pharmacological property of essential oils**

This part of the chapter is huge and covers various aspects of human and animal care. It will be easier to find a disease that no essential oil as a whole or its component can exert any effect. Essential oils are used to manage even diseases that are not scientifically measurable these days. These include protecting against misfortune and bad spirit and protecting the soul after death. This aspect of the therapeutic use of the essential oil will not be described here. The following paragraphs will be

devoted to the review of essential oil use against top 10 human killers. Regarding the classification of 10 global causes of death around the world as published by WHO [57], ischemic heart disease, stroke, chronic obstructive pulmonary disease, lung cancer, diabetes, lower respiratory infection, diarrheal disease, tuberculosis, HIV/AIDS, and road injuries were respectively the most important human killers in 2016. Unfortunately, this chapter could not review the potential of essential oils against road accident.
