In this work, thermal characterization of centrifuged aromatic citrus oils was studied using thermal lens (TL) and open photoacoustic cell (OPC). The thermal diffusivity (D) was obtained by TL, fitting the critical time parameter of the experimental curves to the theoretical values. An experimental arrangement of non-matched mode lasers with a probe laser and an excitation lasers was used. On the other hand, the thermal effusivity (e) of the samples was obtained by using OPC. The thermal conductivity (k) was calculated from the relationship between D and e. The thermal parameters obtained were compared with the theoretical values in the literature. UV-vis spectroscopy, Attenuated Total ReflectanceFourier Transform Infrared spectroscopy (ATR-FTIR) and 1H Nuclear Magnetic Resonance (NMR) were used to determine the absorption coefficients and chemical structure of the citrus oils. The importance of this research work was the determination of the thermal parameters of essential oils as an alternative technique for quality control application.

1. Accepted Manuscript
Title: Thermal properties of centrifuged oils measured by
alternative photothermal techniques
Authors: R. Carbajal-Valdez, J.L. Jim´enez-P´erez, A.Cruz
Orea, Z.N. Correa-Pacheco, M.L. Alvarado-Noguez, I.C.
Romero-Ibarra, J.G. Mendoza ´Alvarez
PII: S0040-6031(17)30235-6
DOI: http://dx.doi.org/10.1016/j.tca.2017.09.014
Reference: TCA 77830
To appear in: Thermochimica Acta
Received date: 11-6-2017
Revised date: 3-9-2017
Accepted date: 13-9-2017
Please cite this article as: R.Carbajal-Valdez, J.L.Jim´enez-P´erez, A.Cruz Orea,
Z.N.Correa-Pacheco, M.L.Alvarado-Noguez, I.C.Romero-Ibarra, J.G.Mendoza
´Alvarez, Thermal properties of centrifuged oils measured by alternative photothermal
techniques, Thermochimica Actahttp://dx.doi.org/10.1016/j.tca.2017.09.014
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
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2. Thermal properties of centrifuged oils measured by alternative
photothermal techniques
R. Carbajal-Valdez1
, J.L. Jiménez-Pérez2,*
, A. Cruz Orea1
, Z. N. Correa-Pacheco3
, M. L.
Alvarado-Noguez4
, I. C. Romero-Ibarra2
, J. G. Mendoza Álvarez1
1
CINVESTAV-IPN, Av. Instituto Politécnico Nacional 2508, Col. San Pedro Zacatenco,
Delegación Gustavo A. Madero, Código Postal 07360, Ciudad de México, México
2
UPIITA, Instituto Politécnico Nacional, Avenida Instituto Politécnico Nacional No. 2580,
Col. Barrio la Laguna Ticomán, Gustavo A. Madero, CP 07340, Ciudad de México, México
3
CONACYT, Centro de Desarrollo de Productos Bióticos-Instituto Politécnico Nacional
(CEPROBI-IPN), Carretera Yautepec–Jojutla, km 6. San Isidro, C.P. 62731, Yautepec,
Morelos, México
4
ESIME, Instituto Politécnico Nacional, Av. Instituto Politécnico Nacional Edificio 5,
Unidad Profesional Adolfo López Mateos, Zacatenco, Delegación Gustavo A. Madero, C.P.
07738, Ciudad de México, México
*
Tel: +52-55-572-6300 ext. 56911, E-mail: jimenezp@fis.cinvestav.mx
Highlights
 Thermal characterization of centrifuged aromatic citrus oils was studied
 Thermal lens (TL) and open photoacoustic cell (OPC) were used for characterization
 Thermal diffusivity, thermal effusivity and thermal conductivity were obtained
 Thermal effusivity and conductivity of green mandarin oil is first time reported
 Absorption coefficients and chemical structure of the citrus oils were determined
Abstract
In this work, thermal characterization of centrifuged aromatic citrus oils was studied using
thermal lens (TL) and open photoacoustic cell (OPC). The thermal diffusivity (D) was
obtained by TL, fitting the critical time parameter of the experimental curves to the
theoretical values. An experimental arrangement of non-matched mode lasers with a probe
laser and an excitation lasers was used. On the other hand, the thermal effusivity (e) of the
samples was obtained by using OPC. The thermal conductivity (k) was calculated from the

3. relationship between D and e. The thermal parameters obtained were compared with the
theoretical values in the literature. UV-vis spectroscopy, Attenuated Total Reflectance-
Fourier Transform Infrared spectroscopy (ATR-FTIR) and 1
H Nuclear Magnetic Resonance
(NMR) were used to determine the absorption coefficients and chemical structure of the
citrus oils. The importance of this research work was the determination of the thermal
parameters of essential oils as an alternative technique for quality control application.
Keywords: thermal diffusivity; thermal effusivity; citrus essential oils; thermal lens; open
photoacoustic cell
1 Introduction
Aromatic essential oils have been used since ancient times in cosmetics, incense or perfumes,
as well as for therapeutic, in medicine (microbial and antispasmodic) and culinary
applications [1-3]. Citrus essential oils are complex mixtures of chemical compounds that
impart characteristic flavor and odor of the fruits. Such chemical compounds can be classified
mainly into three groups: terpenes, sesquiterpenes and oxygenates. However, the chemical
composition depends on cultivation climate, harvest time, the biotype of plant and finally the
process of extracting oils [4-6]. Therefore, it is necessary to determine a profile of the
constituents of essential oils, because the variability in chemical composition determines
their quality. Citrus essential oils are characterized by a volatile and non-volatile fraction,
resulting in a complex product of several hundred compounds. Oils are typically composed
of a mixture of a significant volatile fraction (85–99%) that can be further processed by
distillation and the remaining 1–15% non-volatile residue. The volatiles are composed of
mono- and sesquiterpene hydrocarbons and their oxygenated derivatives, aliphatic
aldehydes, alcohols and esters, whereas the non-volatile fraction contains hydrocarbons,
sterols, fatty acids, waxes, non-volatile terpenes, carotenoids and flavonoids, as well as
coumarins and furocoumarins. The non-volatile residue, which forms from 1% to 15% of the
oil, contains hydrocarbons, sterols, fatty acids, waxes, carotenoids, coumarins, psoralens, and
flavonoids [7]. Industrially, physical characteristics commonly used as the first parameter for
certification are color, taste, odor, density and refractive index. The importance of these
substances and the variety of methods of preparation and purification, like the use of
analytical techniques make necessary to determine their composition and characterize them
for authentication purposes. Among alternative techniques used for these purposes, TL and
OPC are important to determine the thermal properties such as diffusivity, effusivity and
thermal conductivity. In this work, four centrifuged essential oils were studied: lemon,
orange, grapefruit and green mandarin. Our results were compared with the values of the
thermal constants of various essential oils from the literature, obtaining optimal values of
new compositions of citrus oils using two alternative photothermal techniques.
2 Experimental
2.1. Thermal Lens (TL)
The TL spectrometry experimental setup is observed in Fig. 1. The sample is exposed to an
excitation laser beam to generate a local temperature increase and to a probe beam that passes
through the sample. There is an increase in temperature because of the heat produced from

4. the absorbed energy in the sample generating a lens-like optical effect detected by the probe.
The propagation of the probe beam laser through the TL results in either a defocusing or a
focusing of the beam center. Subsequently, the intensity of the probe beam is measured using
a detector [8, 9].
The theory of the TL is expressed in terms of the Fresnell diffraction theory based in the
phase shift on the probe beam after passing through the sample [9-11]. The analytical
expression for the probe beam intensity is as follows:
( ) = (0) 1 −
[( ) ]
(1)
where, I(t) is the time dependence of the probe laser beam at the detector. I(0), is the initial
value of I(t) for t zero, θ is the phase shift of the probe beam after passing through the sample
due to the increase in temperature.
= ; = (2)
where Zc is the confocal distance of the probe beam, Z1 is the distance from the probe beam
waist to the sample. wp is the probe beam spot size and we is the excitation beam spot sizes
at the sample [9].
= − (3)
where Pe is the excitation beam power, Ae is the optical absorption coefficient of the sample
at the excitation beam wavelength, L is the sample thickness, k is the thermal conductivity, λ
is the laser wavelength of the probe beam, and (ds/dT) is the temperature coefficient of the
optical path length change at the probe beam wavelength.
The characteristic time constant of the thermal lens tc depends on the excitation beam spot
size at the sample we, and thermal diffusivity D it can be expressed as:
= (4)
and tc can be determined by fitting the Eq. (1) to the experimental data. The TL was
calibrated with water to compare with the values reported in the literature. The experimental
parameters of TL are summarized in table 1.
2.2. Open photoacoustic cell technique (OPC)
The Open photoacoustic cell technique (OPC) was used for the thermal effusivity
measurements [12]. The thermal effusivity measures essentially the thermal impedance of

5. the sample, or the sample´s ability to exchange heat with the environment. The technique
consists of a modulated beam, obtained with a mechanical chopper, at an angular frequency
of ω = 2πf. The OPC experimental setup is observed in Fig. 2. A detail of the cross section
of the photoacoustic cell is shown in Fig. 3. In the photoacoustic cell, the liquid sample is
placed on the aluminum foil of known thermal effusivity. An electret microphone connected
to the cell detects the heat generated due to the temperature rise and then it diffuses into the
photoacoustic (PA) gas chamber modulating the pressure (acoustic waves) within the PA
cell. A lock-in amplifier interfaced with a data acquisition system measures the microphone-
response signal [13].
For the calculation of the thermal effusivity the obtained photoacoustic signal of each sample
is normalized, by using the photoacoustic signal when the sample is air, and the following
equation is used [14]:
= √ (5)
where is the density of the used aluminum foil (2.7 g cm-3
), is the specific heat of the
aluminum foil (0.9 Jg-1
°C-1
), is the thickness of the aluminum foil (0.0016 cm), = 2
being f the modulation frequency of the excitation beam in the sample, and is the slope of
the normalized photoacoustic signal, as a function of the square root of f. The cell (Fig. 3)
was calibrated with water to compare with the values reported in the literature. The obtained
value for distilled water was (e = 1487.05 ± 47 Ws /
/m °C ) and the reported values
are e = 1640 Ws /
/m °C and e = 1595 Ws /
/m °C [14]). It can be seen, that the
obtained value was similar to the reported values. In the case of the studied essential oils they
contains, among others components, ethanol and the reported thermal effusivity of ethanol is
0.0585 (Ws1/2
/(cm2 o
C)) [15].
Measurements of absorption coefficients and chemical structure were determined by
complementary techniques such as UV-vis spectroscopy, ATR-FTIR and 1
H NMR. 3 Results
and discussion
Different oil batches for the essential oils (lemon, orange, grapefruit and green mandarin)
were used (Chemical aromatic SA Mexico). Essential oils were obtained from the pericarp
of citrus peel by scrapping or breaking the oil cells near the fruit’s surface and using water to
drag the oil in the form of an emulsion, which was centrifuged to obtain the cold pressed oil
[16]. Samples measurements were done at room temperature. A total of 10 measurements
were made for each essential oil under the same conditions.
In Fig 4, the UV-vis spectra of centrifuged citrus oils of lemon, orange, grapefruit, and green
mandarin oils can be seen. An absorbance peak is observed in the region of 300 - 350 nm for
the centrifuged citrus oils due to monoterpene alcohols (terpenes with OH). The bands at 400
- 450 nm and 660 nm are related to the presence of carotenoids and chlorophylls that give
the characteristic color to oil and fruit. The spectra were recorded for essential oils extracted

6. by centrifugation. Changes were observed due to differences in chemical composition of the
different oils [17-18].
In Fig. 5 the ATR-FTIR spectra for the different oils can be seen. Due to the similar chemical
composition of the oils, these spectra showed the typical characteristic absorption bands. The
characteristic absorption bands for essential oils are present: the broad band between 3036-
2784 cm-1
that corresponds to the asymmetrical and symmetrical stretching vibration of the
aliphatic -CH in CH2 and CH3 groups and -OH stretching for alcohol and phenols. At 1743
cm-1
the ester carbonyl functional groups of the triglycerides are assigned. The triglycerides
are the principal components in oils. The most relevant monoterpene components occurring
in these oils are limonene and γ-terpinene, but α - and β -pinene, myrcene, sabinene, octanal,
decanal, citral, sinensal, and nootkatone can also be present [19]. In lemon, orange and
grapefruit essential oils, limonene occurs at levels of approximately 95% and in other citrus
oils at 50–78%. Thus, the ATR-FTIR spectra of these oils are mainly characterized by
limonene vibrational modes to be seen at 877 cm-1
(out-of-plane bending of the terminal
methylene group), at 1442 cm-1
(δ CH2) and at 1644 cm-1
[20]. The individual ν (C=C)
stretching vibrations of both monoterpenes are found at 1658 cm-1
(α -pinene) and 1640 cm-
1
(β-pinene), respectively. Also, α -pinene presents the characteristic signal of the -CH at 787
cm-1
, β-pinene shows the absorption band of the terminal methylene group at 873 cm-1
and
of the cyclohexane ring at 853 cm-1
. Finally, the bands at 800 and 950 cm-1
are associated to
the wagging vibrations of CH and CH2 groups.
Among monoterpenes, numerous aldehyde derivatives can be well recognized by ATR-FTIR
spectroscopy where the intense IR band due to the C=O stretching mode is seen between
1782-1569 cm-1
(blue circle), and the increased ofthe peak at 1158 cm-1
(red circle) for (C=C)
in aromatics. These were observed only for lemon oil compared to the other essential oils.
Figure 6 shows the 1
H NMR spectrum of lemon essential oil. The spectrum shows the
resonances of limonene (Table 2). The signal at 0.66 ppm is attributed to a compound with a
pinenic structure. Then, methylenic protons of all insaturated fatty chains were observed in
the ~1.2 region. In 1.62 and 1.66 ppm there are the squalene and the limonene signals,
respectively. In the inset, the signals at 1.66 and 1.72 shows the limonene contributions
signals. Additionally, other significant correlations were also observed at 5.0 ppm and 2.0
ppm region. It is noticeable that the intensity of 4.7 ppm corresponds to limonene signal. The
sample contains p-cymene with its characteristic resonance at ~7.1 ppm. It is well known that
limonene and p-cymene are components of lemon oil. On area from 9.8 to 10.0 ppm and from
5 to 6 ppm signals were assigned to geranial and neral, two unsaturated aldehydes
characteristic of lemon oil. As shown in Figure 6, neral and geranial displayed many
overlapped signals, but they could be readily distinguished by chemical shifts of the aldehyde
proton (9.9 and 10.0 ppm, respectively), the methyl in cis or trans position (1.98 and 2.17
ppm, respectively) and the overlapping signals observed for CH2 at 2.23 ppm in geranial [21].
Fig.7. shows the 1
H spectrum for the different citric essential oils: orange, grapefruit and
green mandarin. All citric essential oils shown similar spectra. Limonene has been also
determined in the orange, grapefruit and mandarin oils. The 1
H spectrum of these oils is

7. characterized by the presence of the resonance at 4.64 ppm due to =CH2 protons of limonene.
In the 1
H NMR spectrum of mandarin oils, (see the signals in Table 2), the resonances of
limonene (terpene) at 4.64 and 5.37 ppm region and the signal at ~0.7ppm due to a pinenic
structure are present.
From Fig. 8, the transient thermal lens (TL) signal evolutions for citrus oils: lemon, orange,
grapefruit and green mandarin are observed. A decrease of the signal as time passes is
observed. The open circles correspond to the experimental data and the best fit of Eq. (1) to
the experimental data is represented by the red line.
The thermal diffusivity of the citrus oils was measured at room temperature. From the best
fit of Eq. (1) to the experimental data the obtained values were: D = (7.18 ± 0.05) × 10−8
m2
·s−1
, D = (7.22 ± 0.03) ×10−8
m2
·s−1
, D = (7.33 ± 0.03) ×10−8
m2
·s−1
, and D = (7.39
± 0.04) ×10−8
m2
·s−1
citrus oils: lemon, orange, grapefruit, and green mandarin,
respectively. These results are shown in Table 3. These values are in agreement with the
diffusivity values obtained by other analytical techniques [18, 22].
Thermal effusivity values for the samples can be seen in Fig. 9, as an example of the best
fitting of Eq. 5. The obtained values of e were for citrus oils of lemon, orange, grapefruit,
and green mandarin are: (0.0532±0.0026) W・s1/2
・m−2
・o
C−1
, (0.0508±0.0016) W・s1/2
・
m−2
・o
C−1
, (0.0489±0.0011) W・s1/2
・m−2
・o
C−1
, and (0.0646±0.0034) W・s1/2
・m−2
・o
C−
1
, respectively. The reported thermal effusivity of ethanol = 0.0585 (W・s1/2
・m−2
・o
C−1
).
These values agree with the effusivity values obtained with other techniques [22].
As can be seen, the thermal conductivity (k) is the result of the thermal diffusivity (D) and
the thermal effusivity (es) of the sample. The obtained results from Fig. 9 are summarized in
Table 3, where the values for thermal diffusivity (D) and thermal effusivity (e) were used to
calculate the thermal conductivity (k) using the relationship = √ for the different
citrus oils [23].
The obtained values ofthermal diffusivity, effusivity and conductivity for the evaluated citrus
oils are similar to the values reported in the literature with k ranging from 0.130±0.006 to
0.142±0.007 W/m o
C [19]. This slight difference can be related to a variation in chemical
composition of these essential oils related with the extraction process [5, 6]. The measured
values lie in the range of centrifuged essential oils samples, as observed in table 3.
It can be seen from the properties in Table 3, that there is a tendency for the thermal
properties, having lemon oil the lowest value of diffusivity, the highest effusivity and
conductivity. On the other hand, the oil with the highest diffusivity was green mandarin,
having the lowest values of thermal effusivity and conductivity, these two trends are
according to the relation = √ , respectively. From spectroscopic techniques: UV-Vis
spectroscopy, ATR-FTIR and 1
H-NMR results, some changes or differences were observed

8. in characteristic peaks due to the chemical composition of lemon oil, where the most relevant
monoterpene components with respect to the other aromatic oils are present in its structure.
It has been found in the literature that also the percentage of heterocyclic and other
compounds varies greatly among citrus species [26]. Then, the precursor oil used for
photothermal measurements must be taken into account. From ATR-IR and 1
H NMR the
complex chemical structure of citrus oils and factors like pretreatment of peels and different
extraction process such as distillation must be taken into account as studied by other authors
[27].
It is important to highlight, that essential oils are the mixture of different organic molecules.
In the case of our studied citrus oils, chemical composition is similar being limonene the
major component followed by α-pinene, β-pinene and γ-terpinene, among others. Difference
between oils, arises from minority components, which, give different properties according to
their concentration in the essential oil. For example, the group of aldehydes such as neral,
geranial and decanal, among others. Fig 4 shows the UV-vis spectra. As mentioned before,
the bands at 400 - 450 nm and 660 nm are related to the presence of carotenoids, which have
many C=C groups in their structure, and chlorophylls, which includes C=C and C=O
functional groups in different concentrations for the essential oils [18]. From ATR-FTIR
spectroscopy in Fig. 5, an intense band due to the C=O between 1782-1569 cm-1
(blue circle)
was observed. Moreover, an increase of the peak at 1158 cm-1
(red circle) for (C=C) is
observed due to aromatic groups like limonene and γ-terpinene [28]. Some representative
chemical structures of essential oils are observed in Figure 10. The presence of this chemical
compounds were also confirmed by 1H NMR spectra from Figs. 6 and 7. Therefore, behavior
of photothermal properties are attribute to the different functional groups present in the
chemical composition of the oils, being the photothermal techniques an useful alternative to
analyze essential oils and the composition of good quality centrifuged oils.
4. Conclusions
The applications of thermal lens and open photoacoustic cell for study of thermal properties
in citrus oils centrifuged, have been presented. Thermal parameters were evaluated for four
essential oils. Thermal effusivity and conductivity of green mandarin sample are reported for
the first time in the literature. Our results were reproducible compared with the values of the
thermal constants of various essential oils reported in the literature for other photothermal
techniques. Also, results suggest that UV-vis, FTIR and NMR spectroscopy can be good
methods to study the chemical fingerprint of essential oils and to monitor the quality of the
same.
Acknowledgments
Thanks to CONACYT, COFAA, and CGPI-IPN, México, for their partial financial support.
One of the authors (A. Cruz-Orea) is grateful for the economic support of CONACYT
through Project 241330. Also, we thank Ing. Esther Ayala at the Physics Department of
CINVESTAV-IPN for her technical support.

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12. Fig. 1. Themal lens (TL) experimental setup
Fig. 2. Open photoacoustic cell (OPC) experimental setup
Chopper
Ar Laser Photoacoustic
Cell
Lock-In AmplifierData Acquisition
Probe laser
Excitation laser
Lens
Lens
Sample
Lock-in amplifier

13. Fig. 3. Cross section of the open photoacoustic cell (OPC)
Liquid Sample
Acoustic Waves
Metallized Electret Diaphragm
Air Gap
Microphone
Metal Back Plate
Incident
Acrylic Ring
Al Foil
Vacuum
Grease
PA
Chamber

14. 400 500 600 700
0
1
2
3
4
5
LEMON OIL
GREEN MANDARIN OIL
ORANGE OIL
GRAPEFRUIT OIL
Absorption(a.u.)
Wavelength (nm )
Fig. 4. UV-vis spectrum of centrifuged citrus oils: lemon, orange, grapefruit and green
mandarin
4000 3500 3000 2500 2000 1500 1000
-120
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
140
160
-CH
C=CC=O
Transmittance(%)
Wavelength (cm
-1
)
LEMON OIL
GREEN MANDARIN OIL
ORANGE OIL
GRAPEFRUIT OIL
-CH, OH
Fig. 5. FTIR spectra of lemon, green mandarin, orange and grapefruit essential oil samples.

15. Fig. 6. 1
H NMR spectrum of the lemon essential oil (CDCl3, 750 MHz NMR).
6 4 2 0
ORANGE OIL
GRAPEFRUIT OIL
GREEN MANDARIN OIL
Chemical shift (ppm)
Fig. 7. 1
H NMR spectra of the different citric essential oils: orange mandarin, grapefruit, and
green mandarin.

16. 0,0 0,1 0,2 0,3 0,4 0,5 0,6
7,65
7,70
7,75
7,80
7,85
7,90
7,95
8,00
time (s)
LTsignal(V)
D=7.18±0.05 (m
2
/s)
a)
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8
7,3
7,4
7,5
7,6
7,7
7,8
7,9
8,0
time (s)
LTsignal(V)
D=7.22±0.03 (m
2
/s)
b)
0,0 0,2 0,4 0,6 0,8
6,3
6,6
6,9
7,2
7,5
7,8
8,1
time (s)
LTsignal(V)
D=7.33±0.03 (m
2
/s)
c)
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8
7,2
7,3
7,4
7,5
7,6
7,7
7,8
7,9
8,0
8,1
time (s)
LTsignal(V)
D=7.39±0.04 (m
2
/s)
d)
Fig. 8. Transient thermal lens signal for citrus oils: a) lemon, b) orange, c) grapefruit, and d)
green mandarin. Experimental data correspond to open circles. The red line represents the
best fit of Eq. (1) to the experimental data

17. 4.0 4.5 5.0 5.5 6.0 6.5 7.0
0.4
0.6
0.8
1.0
1.2
Slemon
/Sair
sqrt(f) (s
-1/2
)
a)
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
0.6
0.8
1.0
1.2
1.4
Sorange
/Sair
sqrt(f) (s
-1/2
)
b)
5.0 5.5 6.0 6.5 7.0 7.5 8.0
0.8
1.0
1.2
1.4
1.6
Sgrapefruit
/Sair
sqrt(f) (s
-1/2
)
c)
4.0 4.5 5.0 5.5 6.0 6.5
0.5
0.6
0.7
0.8
0.9
d)
Smandaringreen
/Sair
sqrt(f)(s
-1/2
)
Fig. 9. Open cell photoacoustic spectrum of aromatic essential oils thermal effusivities of a)
lemon, b) orange c) grapefruit and d) green mandarin

18. Limonene Geranial Neral Decanal
Fig.10. Main chemical structures of citrus essential oils

19. Table 1.
Thermal lens experiment parameters
Pe - Excitation laser power (at 514.5 nm) 30 mW
Pp - Probe laser power (at 632.8 nm) 1 mW
ωe - Excitation laser spot size 4.9 x 10-3
cm
ω1p -Probe laser spot size at cell 1.81x 10-2
cm
m - Constant parameter 13.691
V - Constant parameter 1.22
Zc – Focal distance 6.56 cm
Z2 - Distance ~2 m
L - Length of sample cell 1.0 cm
Sample Essential Oil
Table 2.
Signals present in 1
HNMR lemon oil spectrum
Signal ppm Lemon oil
Geranial/neral 9.7-10 9.88-10
p-cymene 7.1 7.1
linalool 5.88
limonene 5.3-0.62 4.63, 4.7, 1.73, 1.66,
1.47.
terpene 4.53-4.60 4.60
squalene 1.62 1.62
Methylenic protons of all insaturated fatty
chains
1.25 0.23-1.25
Methylenic protons of palmitic and stearic
fatty chains
1.20 1.18-1.23
wax 0.98 0.97
Methyl of linolenic fatty chains 0.92 0.92
Methyl of linoleic fatty chains 0.84

20. Table 3.
Dependence of thermal diffusivity (D), thermal effusivity (e), thermal conductivity (k) and
fitting parameters (tc and θ) for the different citrus oils.
Essential Oils D(10-8
m2
/s)
Literature [18,22,
24]
D(10-8
m2
/s)
e(104
Ws1/2
/m2
o
C)
Literature [25]
e(104
Ws1/2
/m2
o
C) k(W/m o
C)
Literature [25]
k(W/m o
C)
Lemon 7.18±0.05 7.17±0.05 0.0532±0.0026 0.049 ± 0.003 0.142±0.007 0.134 ± 0.001
Orange 7.22±0.03 7.31±0.03 0.0508±0.0016 0.048 ± 0.002 0.136±0.004 0.132 ± 0.001
Grapefruit 7.33±0.03 7.37±0.02 0.0489±0.0011 0.049 ± 0.003 0.133±0.003 0.137 ± 0.002
Green mandarin 7.39±0.04 7.43±0.08 0.0478±0.0022 - 0.130±0.006 -