hydrophobic ionic liquid-based ultrasound-assisted extraction of magnolol and honokiol from cortex...
TRANSCRIPT
Short Communication
Hydrophobic ionic liquid-based ultrasound-assisted extraction of magnolol andhonokiol from cortex Magnoliae officinalis
The hydrophobic ionic liquid of [BMIM][PF6] was successfully used for the ultrasound-
assisted extraction of hydrophobic magnolol and honokiol from cortex Magnoliae offici-nalis. To obtain the best extraction efficiencies, some ultrasonic parameters including the
concentration of [BMIM][PF6], pH, ultrasonic power and ultrasonic time were evaluated.
The results obtained indicated that the [BMIM][PF6]-based ultrasound-assisted extraction
efficiencies of magnolol and honokiol were greater than those of the [BMIM][BF4]-based
ultrasound-assisted extraction (from 48.6 to 45.9%) and the traditional ethanol reflux
extraction (from 16.2 to 13.3%). Furthermore, the proposed extraction method is validated
by the recovery, correlation coefficient (R2) and reproducibility (RSD, n 5 5), which were
90.8–102.6, 0.9992–0.9998, and 1.6–5.4%, respectively.
Keywords: Honokiol / Ionic Liquid / Magnoliae officinalis / Magnolol /Ultrasound-assisted extractionDOI 10.1002/jssc.201000076
1 Introduction
Magnolia officinalis Rehd. et Wils., the Chinese name of
Houpo, is one kind of popular herbal medicine and officially
listed in the Chinese Pharmacopoeia [1]. It has been proved
to be effective in the treatment of many diseases including
anxiety and nervous disturbance, thrombotic stroke, typhoid
fever and dead muscle [2, 3]. Magnolol and honokiol
(Figs. 1A and B), the main bioactive constituents of the
medicinal plant, have multiple therapeutic effects and
pharmacological activities such as anti-anxiety, anti-depres-
sion, anti-oxidant, anti-inflammatory, anti-bacteria, anti-
platelet, anti-arrhythmia, anti-tumor, anti-cancer, etc. [2, 4].
Heat-reflux extraction [2] is the most widely used tech-
nique for the extraction of magnolol and honokiol from
cortex M. officinalis. However, this traditional extraction
method is laborious, time-consuming and solvent-consum-
ing. Recently, ultrasonic-assisted extraction and microwave-
assisted extraction have been introduced for the alternative
extraction method of heat-reflux extraction. Compared
with the microwave-assisted extraction, ultrasonic-assisted
extraction does not require expensive apparatus and
complicated operation [5] so that it gained more attention in
the extraction of target compounds [6–8].
In recent years, ionic liquids have received much
attention as a novel class of effective solvent media alter-
native to organic solvents [9–12]. Especially, ionic liquid-
based extraction has been applied in the extraction of
bioactive compounds from medicinal plant [13–15].
However, these experiments all dealt with the hydrophilic
ionic liquid-based extraction of hydrophobic target
compounds, which seems to deviate from the dissolution
rule of similarity. For this purpose, hydrophobic
[BMIM][PF6] was tested for the extraction of hydrophobic
magnolol and honokiol from cortex M. officinalis.
2 Materials and methods
2.1 Reagents and materials
Purchased from the National Institute for the Control of
Pharmaceutical and Biological Products (Beijing, China),
the reference compounds of magnolol and honokiol were
dissolved in methanol and then stored at �201C. Ionic
liquids of 99.0% 1-butyl-3-methylimidazolium hexafluoro-
phosphate ([BMIM][PF6]) and 1-butyl-3-methylimidazolium
tetrafluoroborate ([BMIM][BF4]) were ordered from Shang-
hai Chengjie Chemical (Shanghai, China) and used directly.
Other reagents were at least of analytical grade and used
directly. Doubly distilled water was used throughout the
whole experiments.
The medicinal material of cortex M. officinalis was
obtained by Jianlian drug store (Jinan, China), which
Lijin Zhang1
Xiao Wang2
1Department of Food Science,Tianjin Agricultural University,Tianjin, P. R. China
2Shandong Analysis and TestCenter, Shandong Academy ofSciences, Shandong, P. R. China
Received February 3, 2010Revised April 13, 2010Accepted April 14, 2010
Correspondence: Dr. Lijin Zhang, Department of Food Science,Tianjin Agricultural University, No. 22 Jinjing Road, XiqingDistrict, Tianjin 300384, P. R. ChinaE-mail: [email protected]: 186-22-2378-2596
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
J. Sep. Sci. 2010, 33, 2035–2038 2035
species was confirmed by Dr. Jia Li (Shandong University of
Traditional Chinese Medicine, Jinan, China).
2.2 Apparatus
All ultrasound-assisted extractions were carried out on a
variable power ultrasound cleaning bath of Kotter-KT-300Y
(40 cm� 20 cm� 10 cm internal dimensions water bath,
Jining Kotter Ultrasonic Electron, Jining, China). The HPLC
analysis was performed by Waters 600 Millennium32 system
including a Waters 996 photodiode array detection (DAD)
system, a Waters 600 multisolvent delivery system, a Waters
600 system controller, a Waters 600 pump and a Millen-
nium32 workstation (Waters, Milford, MA, USA).
2.3 Ionic liquid-based ultrasound-assisted extraction
200 g dried and homogenized cortex M. officinalis sample
was ground into powder. [BMIM][PF6] was dissolved in
lower polar and nontoxic ethanol considering its solubility
and its viscosity. About 20mL ethanol solutions of
[BMIM][PF6] and 1.0 g sample powder were prepared for
the ultrasound-assisted extraction, the ultrasonic tempera-
ture of which was kept constant by the replacement between
inlet and outlet water. The optimum extraction conditions
were systematically studied in this study. Each extract was
filtrated through a 0.45 mm filter for subsequent HPLC
analysis. To demonstrate the advantage of the hydrophobic
ionic liquid-based extraction efficiencies of magnolol and
honokiol, aqueous solution of [BMIM][BF4]-based extraction
was also carried out under the same extraction conditions.
2.4 Traditional reference extraction method
Furthermore, the traditional ethanol reflux extraction was
supplied as the reference extraction. That is, 1.0 g sample
powder was extracted by 20 mL refluxing ethanol for 2 h,
during which the refluxing ethanol was kept constant by
continuously adding ethanol. After three times of extrac-
tions, the extract of ethanol reflux was combined, concen-
trated to 20 mL and filtrated through a 0.45 mm filter for
subsequent HPLC analysis.
2.5 Chromatographic condition
The chromatographic column was a Waters Symmetry-
shield RP18 (250 mm� 4.6 mm id, 5 mm), the eluent was a
mixture of methanol and 0.5% acetic acid (80:20, v/v), the
flow rate was 1.0 mL/min, the injection volume was 10 mL
and the column effluent was monitored at the wavelength of
290 nm. All chromatographic measurements were operated
at room temperature.
3 Results and discussion
3.1 Effect of solvent concentration on extraction
The [BMIM][PF6]-based extraction behavior is due to its
dissolving ability for hydrophobic magnolol and honokiol
and its distinct multiple interactions with target compounds
including dispersive interaction and hydrogen bonding [16].
The extraction efficiencies of magnolol and honokiol in
Fig. 2A increased with the increase of concentration from 0
to 2.0 mol/L, whereas the extraction efficiencies decreased
with a further increase of concentration from 2.0 to
3.0 mol/L, which can be explained by the fact that excessive
[BMIM][PF6] is too viscous to penetrate through the powder
sample. According to this, 2.0 mol/L [BMIM][PF6] was used
in the following study.
3.2 Effect of pH on extraction
pH determines the existence of phenolic magnolol and
honokiol in the ethanol solution, which influences the
corresponding interaction between [BMIM][PF6] and the
phenolic compounds. The effect of pH on the extraction
efficiencies is shown in Fig. 2B, meaning that the change of
pH had no significant effect on the extraction efficiencies of
magnolol and honokiol. Therefore, the pH was set at 7.15 in
the following study.
3.3 Effect of ultrasonic power on extraction
Ultrasonic power plays an important role in the complete
dispersion of solvent medium into the solid sample. Figure
2C shows that the maximum extraction efficiencies of
magnolol and honokiol were achieved at 200 W of ultrasonic
bath. When the ultrasonic power was higher than 200 W,
there was no significant increase of the extraction efficien-
cies. Therefore, the ultrasonic power of 200W was enough
for the maximum extraction efficiencies of magnolol and
honokiol from cortex M. officinalis.
OH OH OH
OH
A B
Figure 1. Chemical structure of magnolol (A) and honokiol (B).
J. Sep. Sci. 2010, 33, 2035–20382036 L. Zhang and X. Wang
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
3.4 Effect of ultrasonic time on extraction
To some degree, the ultrasonic time is in direct proportion
to the extraction efficiency. The extraction results in Fig. 2D
show that the extraction efficiencies of magnolol and
honokiol increased within the first 30 min and longer
extraction time did not produce higher extraction efficien-
cies. In view of this, 30 min is the appropriate extraction
time.
3.5 Comparison of the proposed approach with the
traditional method
In order to investigate the advantage of [BMIM][PF6], a
series of extraction experiments were carried out under the
same ultrasound-assisted extraction conditions. Compared
with the extraction efficiencies of magnolol and honokiol
obtained by the [BMIM][BF4]-water extraction, [BMIM][PF6]-
ethanol extraction provided higher extraction efficiencies
(48.6 and 45.9% enhanced), respectively. When compared
with the traditional ethanol reflux extraction, the proposed
approach still offered higher extraction efficiencies (16.2 and
13.3% enhanced) and shorter extraction time (330 min
reduced). This means that the proposed [BMIM][PF6]-based
ultrasound-assisted extraction is a rapid and efficient
extraction approach of magnolol and honokiol from the
cortex M. officinalis.
3.6 Method validation
To evaluate the proposed [BMIM][PF6]-based ultrasound-
assisted extraction approach, the linearity, reproducibility,
LOD and extraction efficiencies of magnolol and honokiol
were evaluated by spiked sample. As summarized in Table 1,
linear range of magnolol and honokiol was 5.76–300.00 and
3.32–200.00 mg/L, their correlation coefficient of the
regression lines was from 0.9992 to 0.9998 and the LOD
was from 0.043 to 0.068 mg/L, which was approximately
equal to the LODs of the literature values [17, 18].
Furthermore, Table 2 summarizes that the recovery ranged
from 90.8 to 102.6% and the RSD was lower than 5.4%. All
of the above suggested the reliability of the present method.
Table 1. Calibration curves, linear range, correlation coefficients and LODs of magnolol and honokiol
Components Calibration curve Linear range (mg/L) Correlation coefficient (R2) LODs (mg/L)
Magnolol y 5 8359.2x14097 5.76–300.00 0.9992 0.068
Honokiol y 5 5329.7x11773 3.32–200.00 0.9998 0.043
0
20
40
60
80
100
80 150 200 250 300 350Ultrasonic power(W)
Etr
act
ion
effi
cie
nci
es(
%)
0
20
40
60
80
100
10 20 30 40 50 60 90Ultrasonic time(Minutes)
Ext
ract
ion
effic
ienc
ies(
%)
0
20
40
60
80
100
0 0.5 1.0 1.5 2.0 2.5 3.0
Concentration of [BMIM][PF6](mol/L)
Ext
ract
ion
effic
ienc
ies(
%)
0
20
40
60
80
100
1.15 4.15 7.15 9.55 12 15 18
pH
Ext
ract
ion
effic
ienc
ies(
%)
A B
C D
Figure 2. (A) Effect of the [BMIM][PF6]concentration on the [BMIM][PF6]-basedultrasound-assisted extraction efficiency.(B) Effect of pH on the [BMIM][PF6]-based ultrasound-assisted extraction effi-ciency. (C) Effect of ultrasonic power onthe [BMIM][PF6]-based ultrasound-assistedextraction. (D) Effect of ultrasonic time onthe [BMIM][PF6]-based ultrasound-assistedextraction. (The extraction efficiency isexpressed as the observed value of magnololand honokiol and the maximum amount ineach curve was considered to be 100%.)
J. Sep. Sci. 2010, 33, 2035–2038 Sample Preparation 2037
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com
4 Concluding remarks
A green and effective method of the hydrophobic
[BMIM][PF6]-based ultrasound-assisted extraction has been
developed for the extraction of magnolol and honokiol from
cortex M. officinalis. Compared with [BMIM][BF4]-based
ultrasonic-assisted extraction and conventional heat reflux
extraction, the proposed approach proved to be more
effective in view of the extraction efficiencies and extraction
time. Furthermore, the spiked test revealed that the
proposed extraction was suitable for the effective extraction
of magnolol and honokiol from cortex M. officinalis.
The authors have declared no conflict of interest.
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Table 2. Yields of magnolol and honokiol under optimized
extraction conditions (n 5 5)
Spiked (mg) Recovery (%) RSD (%)
Magnolol Honokiol Magnolol Honokiol
5.0 97.7 93.2 2.9 5.4
10.0 102.6 90.8 3.2 1.6
20.0 95.8 96.1 2.7 4.1
J. Sep. Sci. 2010, 33, 2035–20382038 L. Zhang and X. Wang
& 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com