Synthesis of magnetic multiwall carbon nanotubes for enantioseparation of three pesticide residues in fruits and vegetables by chiral liquid chromatography

Article abstract of DOI:10.1002/chir.23029

In this study, magnetic multiwalled carbon nanotubes (MMWCNTs) were synthesized and used as adsorbent for preconcentration of chiral pesticide residues (including epoxiconazole, tebuconazole, and metalaxyl) in lettuce, cabbage, and apple. Several parameters affecting the treatment efficiency were investigated, including extraction solvent and absorption solvent. Under the optimal conditions, all three chiral pesticides showed decent enantiomeric separation (Rs?>?1.48). The linearity of each target was good with the correlation coefficient (r²) being greater than 0.9923. The average recoveries of the three spiked levels were 73.4% to 110.9% with repeatability (RSD_r) less than 7.6%, and the limit of quantification of the method was 0.10 to 0.25?mg·kg^?1. The results indicated that MMWCNTs had a good purifying effect, which can be applied as an effective pretreatment tool for the determination of residual chiral pesticides in fruits and vegetables.

Full text of DOI:10.1002/chir.23029

Received: 29 June 2018
DOI: 10.1002/chir.23029
Revised: 29 August 2018
Accepted: 3 October 2018
R E G U L A R A R T I C L E
Synthesis of magnetic multiwall carbon nanotubes for
enantioseparation of three pesticide residues in fruits and
vegetables by chiral liquid chromatography
Shuo Lei1 | Xianhui Li1 | Yang Wang1 | Lirong Sun2 | Hao Liu2 | Longshan Zhao1
1 School of Pharmacy, Shenyang
Abstract
Pharmaceutical University, Shenyang,
In this study, magnetic multiwalled carbon nanotubes (MMWCNTs) were syn-
thesized and used as adsorbent for preconcentration of chiral pesticide residues
(including epoxiconazole, tebuconazole, and metalaxyl) in lettuce, cabbage,
and apple. Several parameters affecting the treatment efficiency were investi-
gated, including extraction solvent and absorption solvent. Under the optimal
conditions, all three chiral pesticides showed decent enantiomeric separation
(Rs > 1.48). The linearity of each target was good with the correlation coeffi-
cient (r2) being greater than 0.9923. The average recoveries of the three spiked
levels were 73.4% to 110.9% with repeatability (RSDr) less than 7.6%, and the
limit of quantification of the method was 0.10 to 0.25 mg·kg−1. The results indi-
cated that MMWCNTs had a good purifying effect, which can be applied as an
effective pretreatment tool for the determination of residual chiral pesticides in
fruits and vegetables.
China
2 Central Laboratory, Tongliao
Agricultural and animal Products Quality
Safety Center, Tongliao, China
Correspondence
Longshan Zhao, School of Pharmacy,
Shenyang Pharmaceutical University, 103
Wenhua Road Shenhe District, Shenyang,
China.
Email: longshanzhao@163.com
Funding information
National Natural Science Foundation
of China, Grant/Award Number:
No. 81503029; Shenyang Pharmaceutical
University, Grant/Award Number:
ZQN2016011; Young and Middle‐aged
Backbone Personnel Training Program of
Shenyang Pharmaceutical University,
Grant/Award Number: ZQN2016011;
National Natural Science Foundation of
China, Grant/Award Number: 81503029
KEYWORDS
carbon nanomaterials, chiral resolution, garden stuff, hazard residues, pretreatment
1 | INTRODUCTION
and separation of enantiomers for the detection and con-
trol of chiral pesticides.
Pesticides are widely applied to control pests of fruits and
vegetables, which becomes a main problem in food safety.
Since more than 1000 pesticides are currently in use
around the world, it is estimated that chiral pesticides in
China account for more than 40% of pesticides used at
present.1,2 Although the physical and chemical properties
are identical for the pair of enantiomers, different enantio-
mers tend to exhibit different bioactivity and toxicity in
biosystems.1 One may represent high biological activity,
whereas the other may be inefficient or even toxic to non-
target organisms. However, the majority of pesticides com-
mercially available are racemates. Accordingly, it is
significant to establish an effective method for extraction
For the pesticides in fruits and vegetables, it is chal-
lenging to develop an effective method to extract and ana-
lyze since they occur in complex matrixes at trace levels. A
number of methods have been used to deal with complex
matrixes such as: solid phase extraction (SPE),3-5 matrix
solid‐phase dispersion (MSPD),6-8 quick, easy, cheap,
effective, rugged, and safe (QuEChERS) method,1,9,10 and
ultrasound‐assisted solvent extraction.11-13
The SPE technology is one of the most frequently
used approaches for cleanup of pollutants, owing to the
advantages such as high enrichment factor and low
organic solvent consumption.14 China has promulgated
many standards for testing pesticide residues in fruits
Chirality. 2018;1–9.
wileyonlinelibrary.com/journal/chir
© 2018 Wiley Periodicals, Inc.
1

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LEI ET AL.
and vegetable crops, of which the solid‐phase extraction
technology are used as pretreatment method.15 However,
in SPE procedure, the selection of appropriate sorbent is a
significant factor, which affects recovery and enrichment
factor. In addition, because of the limit of mass transfer
rate, extraction processes of ordinary SPE is time‐
consuming in some cases.16,17
In recent years, QuEChERS method has gradually
become a common method for extracting pesticide resi-
dues, which means quick, easy, cheap, effective, rugged,
and safe. Although commercialized QuEChERS device
is convenient, it is disposable with high cost. Therefore,
it is necessary to establish an efficient, convenient, and
cheap pretreatment method for the extraction of pesticide
residues in complex matrix samples.
In this study, MMWCNTs were synthesized by chem-
ical coprecipitation method and chracterized by Fourier
transform infrared spectroscopy (FTIR) characterization,
magnetization curve, and magnet adsorption phenome-
non. The performance of the prepared particles was
evaluated by extracting three chiral pesticides in
lettuce, cabbage, and apple. An enantioselective high‐
performance liquid chromatography with ultraviolet
detection (HPLC‐UV) method was developed for the
separation
using
CHIRALCEL
OJ‐H
column
(4.6 mm × 250 mm, I.D. 5 μm). To the authors' knowl-
edge, such a method based on MMWCNTs for the extrac-
tion of pesticides from fruits and vegetables has never
been exploited.
Carbon nanotubes have been received research inter-
est among scientists since they were discovered by Iijima
in 1911. Their application and synthesis system have been
explored and refined since then. Carbon nanotubes can
be categorized into single‐walled carbon nanotubes
(SWCNTs) and multiwalled carbon nanotubes
(MWCNTs). Because MWCNTs have large specific sur-
face area, they possess strong adsorption capacity and
high enrichment ability for the absorption of pesticide
residues, metal compounds, and polycylic aromatic
hydrocarbons.18 Zhao et al extracted pesticide residues
in vegetables using MWCNTs as solid‐phase extraction
sorbent. Their results showed that the analytes were
quantitatively extracted with satisfactory recoveries and
cleanup effect from those complex matrixes.19
Hadjmohammadi et al compared the adsorption capacity
and enrichment factor of MWCNT with C18 as adsorbing
material in SPE process. Their results demonstrated that
MWCNT had higher extraction efficiency and lower
detection limit toward C18 material.20 Although
MWCNTs have satisfactory adsorption and clean‐up abil-
ity, their separation from sample solutions is often diffi-
cult and time‐consuming.21 In order to overcome this
flaw, magnetization technology was introduced to avoid
redundant separation approach. Magnetic multiwalled
carbon nanotubes (MMWCNTs) were then synthesized,
which have both magnetic nanoparticles and carbon
nanotube structure.16 A unique advantage of this technol-
ogy is that the particles can be rapidly isolated from sam-
ple solution in an external magnetic field after adsorbing.
2 | MATERIALS AND METHODS
2.1 | Chemicals and reagents
Carboxyl‐functionalized multi‐walled carbon nanotubes
(MWCNT‐COOHs) were purchased from Chengdu
Organic Chemistry Co Ltd, Chinese Academy of
Sciences (Chengdu, China). Racemic epoxiconazole,
tebuconazole, and metalaxyl (Figure 1) (all 95% purity)
were brought from Shandong Weifang Runfeng
Chemical Co, Ltd (Shandong, China). The pesticide
stock solutions were prepared in n‐hexane (HPLC
grade) at a concentration of 1 mg/mL and kept at 4°C.
Ammonium sulfate dodecahydrate (NH4Fe(SO4)2·12H2O)
and
ammonium
ferrous
sulfate
hexahydrate
((NH4)2Fe(SO4)2·6H2O) were offered by Hengxing
Chemical Reagent Factory (Tianjin, China). Ammonia,
methylene chloride, toluene, methanol, n‐hexane,
acetonitrile, and isopropanol andacetic acid were of ana-
lytical grade and supplied by Yuwang Industrial Co, Ltd
(Shandong, China). Hexane and isopropanol of HPLC
grade were supplied by Concord Technology Co, Ltd
(Tianjin, China).
2.2 | Sample preparation
Lettuces, cabbages, and apples were purchased from local
market in Shenyang, and the edible parts were mashed
and homogenized. Afterwards, the homogenates were
FIGURE 1 Structures of three chiral
pesticides

LEI ET AL.
3
then placed respectively in 500 mL round bottom flasks
and frozen for 12 hours before being freeze‐dried. The
resulting dry powders were put into jars for later use.
2.3 | Preparation and characterization of
MMWCNTs
One gram of MWCNT was suspended into 200 mL of
mixed solution containing 1.7 g (NH4)
Fe (SO4)
2
2·6H2O and 2.51 g NH4Fe(SO4) ·12H O. Under the pro-
2
2
tection of nitrogen, ammonia solution was added
dropwise to control the pH of the solution above 11.
Afterwards, the mixture was sonicated for 15 min, and
then mechanically stirred for 30 min on a temperature
controlled water bath at 50°C. After reaction, the
obtained MMWCNTs were collected by magnet isolation
and rinsed three times with distilled water and absolute
ethanol, respectively, and then dried under vacuum at
50°C.
The surface chemistry of MMWCNTs and MWCNTs
were studied using FTIR spectrum (Figure 2). Compared
with the spectrum of bare MWCNTs, the FTIR spectra
of MMWCNTs composites appeared at 584.7 cm−1 for
Fe–O characteristic band, 3427.7 cm−1 for O–H stretching
band, and 1384.3 cm−1 for –CH3 stretching band, indicat-
ing the MMWCNTs were composed of oxidized MWCNT
and iron oxide.16,22
Determination of magnetization curve is another
potent method to evaluate magnetic property of magnetic
materials. Typical magnetization curve of the modified
MMWCNTs is shown in Figure 3. Clearly, the curve has
no hysteresis, suggesting that the particles are
superparamagnetic.21 The composite has a saturation
magnetization of 38 emu·g−1, which validates its good
FIGURE 3 Hysteresis loop diagram of magnetic multiwalled
carbon nanotubes
magnetic property. What is more, the cluster of particles
in external magnetic field (Figure 4) reflects its satisfac-
tory magnetic property.
2.4 | Chromatographic conditions
Three pesticides (epoxiconazole, tebuconazole, and
metalaxyl) were quantified using chiral liquid chromatog-
raphy with a UV detector. The chromatography column
was CHIRALCEL OJ‐H column (4.6 mm × 250 mm, I.
D. 5 μm) provided by Daicel Chiral Technologies Co,
Ltd (Tokyo, Japan). The chiral separation was carried
out under gradient elution condition, and the following
gradient conditions were used: n‐hexane: isopropanol
(95:5, v/v) originally, then a linear gradient to n‐hexane:
isopropanol (80:20, v/v) until 30 min, followed by a linear
gradient from n‐hexane: isopropanol (80:20, v/v) to n‐
hexane: isopropanol (95:5, v/v) until 45 min. The flow
FIGURE 2 IR spectra characterization of multiwalled carbon
nanotubes and magnetic multiwalled carbon nanotubes
FIGURE 4 Actual magnetic phenomenon

4
LEI ET AL.
rate was 0.8 mL·min−1 constantly. The eluent was moni-
tored using UV detection at a wavelength of 230 nm.
3 | RESULTS AND DISCUSSION
3.1 | Optimization of pretreatment
procedure
2.5 | Pretreatment procedure
2.5.1 | Extraction procedure
3.1.1 | Optimization of extraction solvent
The type of extraction solvent might have direct impacts
on the recoveries. The selection depends mainly on the
structure of the analytes and their solubility. In this
experiment, three kinds of solvents with good solubility
for the pesticides were selected: dichloromethane, tolu-
ene, and methanol. The effects of different extraction sol-
vents on the recovery rate were investigated and the
result is shown in Figure 5A. Obviously, the best extrac-
tion efficiency was obtained when dichloromethane was
used as the extraction solvent. Thus, pesticides in fruit
and vegetable samples were extracted with dichlorometh-
ane by sonication.
One gram of freeze‐dried powder was added into a 50‐mL
centrifuge tube and extracted with 20‐mL dichlorometh-
ane by ultrasonic for 30 min. The mixture was then cen-
trifuged at 4000 rpm for 10 min. The supernatant was
collected, and the residue was extracted again. The super-
natant was combined and evaporated under nitrogen
stream at 40°C, then dissolved by 20 mL of n‐hexane.
2.5.2 | Magnetic clean‐up procedure
Eighty milligrams of MMWCNTs were added to the sam-
ple extract. The mixture was sonicated for 2 min, and
then shaken for 30 min at 40°C water bath heating. After
the oscillating, the composites were isolated by a magnet
on the outer wall of the centrifuge tube, and the superna-
tant was discarded. The remained carbon nanotubes were
then washed with 2‐mL methanol by ultrasonicating for
15 min. The washing operation was repeated for three
times. Afterwards, the supernatants were combined, and
then evaporated to dryness under nitrogen stream at
40°C. The residue was diluted to 200 μL with n‐hexane:
isopropanol (95:5, v/v). Finally, 20 μL of the sample solu-
tion was injected into HPLC.
3.1.2 | Optimization of absorption solvent
The type of adsorption solvent also plays a significant role
in the extraction efficiency. It is expected that the selected
solvents have certain solubility of the pesticides to be
tested, so as to facilitate the adsorption of pesticides by
MMWCNTs. In this study, acetonitrile, n‐hexane, and
isopropanol were selected as alternative adsorption sol-
vents. The results showed that the highest extraction
recovery when n‐hexane was used (Figure 5B). In addi-
tion, the vegetable extracts changed from to colorless
FIGURE 5 Optimization of the pretreatment process: A, extraction solvent; B, absorption solvent; C, amount of MMWCNTs; D, eluent; E,
elution time. The text in abscissa is as follows: a dichloromethane, toluene, methanol; b n‐hexane, acetonitrile, isopropanol; c 20, 40, 60, 80, 100;
d CH2Cl2, CH2Cl2‐acetic acid, methanol, methanol‐acetic acid; e 5, 10, 15, 20

LEI ET AL.
5
after adsorption by n‐hexane. Given the above, pesticides
in samples were extracted with n‐hexane.
pesticides. The correlation coefficients (r2) for all pesti-
cides enantiomers ranged from 0.9923 to 0.9998, which
meant good linearities of the method (Table 1). The
LOQ was selected as the lowest spike level for which true-
ness was in the range of 70% to 120% and reproducibility
below 20%. LOQ was set at 0.25 mg·kg−1 for metalaxyl
and tebuconazo, and 0.10 mg·kg−1 for epoxiconazole. In
this study, the weight of matrix is calculated on the basis
of freeze‐dried powder. As the weight of fruits and vegeta-
bles reducing substantially in the freeze‐drying process, it
meant that LOQs might be higher than that of the
methods extracting directly. All of the three pesticides
attained satisfactory resolution (Figure 6).
Trueness was calculated on five replicates and ranged
from 73.4% to 110.9% with the repeatability (RSDr) vary-
ing from 1.3% to 7.6%. The within‐laboratory reproduc-
ibility (RSDwR) was measured over 3 days. As shown in
Table 2, all precision values fulfilled the analytical
requirements regulated in the SANTE 11813/2017. It sug-
gests that as a novel adsorbent material, MMWCNTs have
adequate capability to adsorb analytes thoroughly, which
can be used as an effective pretreatment tool for the
determination of contaminants in complex matrix.
The retention time of the analyte in the spiked sample
was compared with that of the calibration standard. The
deviations are shown in Table 3. The deviations were
thought to be acceptable within 0.1 min according to
SANTE 11813/2017.
3.1.3 | Optimization of the amount of
MMWCNTs
The effects of the amount of MWCNTs on the recovery
were carefully investigated at a fortification concentration
of 10 mg·kg−1 (Figure 5C). As shown in the diagram, the
recovery increased as the amount of MMWCNTs ranging
from 20 to 80 mg. When the amount increased above
80 mg, the recovery remained constant almost. Therefore,
80 mg of magnetic particles were added in the following
experiments considering that the adsorption was greatest
when this dosage was used.
3.1.4 | Optimization of the eluent
Different eluent has certain effect on the recovery rate.
Four organic solvents including dichloromethane,
dichloromethane‐acetic acid (95:5, v/v), methanol, and
methanol‐acetic acid (95:5, v/v) were investigated for their
elution capacity. As the results shown in Figure 5D, the
acetic acid could improve the recovery of compounds.
However, the solution always contained precipitation
after being evaporated and dissolved when acetic acid
was added, which made it difficult to filtrate through a
0.45‐μm micron filter. Take all the factors into account,
methanol was chosen as eluent in order to get satisfactory
results.
3.3 | Comparison among MMWCNTs and
other absorbents
3.1.5 | Optimization of the elution time
In order to further demonstrate the superiority of the
method, the sorption capacity on MMWCNTs were com-
pared with MWCNTs in this study. It can be seen in
Figure 7, the recovery of metalaxyl was higher when
MMWCNTs were used as absorbents, whereas that of
tebuconazole and epoxiconazole were slightly lower. This
phenomenon might be due to two reasons: on the one
Elution time is another influential parameter on the
extraction recovery. In general, extraction recovery
improves with the elution time increasing. However, on
the negative side, the structure of MMWCNTs may be
destroyed simultaneously. Therefore, the influence of elu-
tion time varying from 5 to 20 min was tested. As shown
in Figure 5E, extraction efficiency reached maximum at
15 min. Therefore, 15 min was used to elute in subse-
quent experiments.
TABLE 1 Specificity, sensitivity, and linearity of the proposed
method
LOQ
Linearity
Compounds
tR (min) (mg·kg−1
)
(mg·kg−1
)
r2
3.2 | Method validation
Metalaxyl E1
Metalaxyl E2
18.841
24.130
0.25
0.25
0.25
0.25
0.10
0.10
0.5‐20
0.5‐20
0.5‐20
0.5‐20
0.5‐20
0.5‐20
0.9996
0.9998
0.9998
0.9995
0.9923
0.9992
The developed method was validated under optimum
conditions based on linearity, limits of quantification
(LOQs), trueness, precision, and retention time referring
to SANTE 11813/2017.
The linearity was established at five concentration
levels in the range of 0.5 to 20 mg·kg−1 for all of the
Tebuconazole E1 21.449
Tebuconazole E2 31.309
Epoxiconazole E1 26.479
Epoxiconazole E2 33.059

6
LEI ET AL.
FIGURE 6 Enantioseparation
chromatograms of three chiral pesticides:
A, Metalaxyl, B, Tebuconazole,
C, Epoxiconazole
hand, the specific surface area (SSA) of MWCNT was
larger than that of the same weight of MMWCNT on
which were iron oxides covering.23 On the other hand,
in the process of the experiment, different adsorbents
were weighed in the same quality, while the volume of
MWCNTs was almost twice than that of the MMWCNTs.
That is to say, the attachment of iron oxide leads to sub-
stantial extra weight. Despite these, a significant advan-
tage of being conveniently isolated from solution made
MMWCNT a promising adsorbent to remove pollutant
from matrix.
adsorbent16,17 is generally not more than 100 mg. It
reflects the high uptake capacity of the latter. In addition,
MMWCNTs can be regenerated in comparison with
many other methods. Experiments showed that after
repeatedly adsorption–desorption experiments, the recov-
ery of MMWCNT can still achieve satisfactory results.8,23-
25
To sum up, MMWCNT can greatly reduce scientific
research cost.
3.4 | Real sample analysis
Some other common pretreatment methods such as
SPE, MSPD, and QuEChERS method are the methods
that developed in recent years. Their theories are identi-
cal to that of MMWCNT. In general, the amount of their
adsorbent ranges from a few hundred milligrams to sev-
eral grams, whereas the amount of MWCNT
The newly developed method was applied to analyze veg-
etables and apple samples obtained from local market in
Shenyang (China). The results showed that there were
no samples found to be contaminated with target
pesticides.

LEI ET AL.
7
TABLE 2 Accuracy and precision of the proposed method
Intraday
Day 2
Interday
RSDwR
(%)
Day 1
Day 3
Average (%)
Spiked
(mg·kg−1
Compounds
)
Average (%)
RSDr(%)
Average (%)
RSDr (%)
RSDr (%)
Metalaxyl E1
8
10
12
74.7
73.4
76.3
1.7
4.1
1.7
74.2
79.7
74.7
1.8
1.5
2.2
73.0
75.2
76.7
3.0
4.5
1.3
1.2
4.3
1.5
Metalaxyl E2
8
10
12
94.7
93.8
94.4
3.9
2.1
2.7
91.1
95.2
92.1
3.5
2.3
2.1
102.5
93.4
103.5
2.0
2.2
4.4
6.1
1.1
3.6
Tebuconazole E1
Tebuconazole E2
Epoxiconazole E1
Epoxiconazole E2
8
10
12
104.5
103.3
90.5
2.2
4.7
4.2
99.2
102.3
99.6
2.5
1.8
1.4
94.0
86.7
90.7
1.7
4.7
1.7
2.8
5.2
7.2
8
10
12
88.5
93.8
96.2
4.1
3.9
1.9
92.6
94.2
94.7
3.7
4.3
2.4
89.9
99.8
104.1
3.9
2.1
2.7
2.4
3.5
5.2
8
10
12
101.8
108.2
100.5
2.2
6.3
2.9
99.9
110.9
96.2
1.3
5.8
3.9
102.2
109.9
98.2
3.0
6.0
3.3
1.3
1.3
2.3
8
10
12
90.8
94.8
97.0
2.4
1.4
7.6
89.7
91.7
95.2
2.3
2.9
2.0
87.8
91.8
92.4
2.8
1.6
4.1
1.8
2.0
2.5
TABLE 3 Deviation of retention time of the proposed method
Retention Time of
Extract (min)
Retention Time of
Calibration (min)
Compounds
Deviation
Metalaxyl E1
18.841
18.802
24.161
21.423
31.348
26.389
32.974
0.039
−0.031
0.026
Metalaxyl E2
24.130
21.449
31.309
26.479
33.059
Tebuconazole E1
Tebuconazole E2
Epoxiconazole E1
Epoxiconazole E2
−0.039
0.090
0.085
4 | CONCLUSION
In the current investigation, MMWCNTs were synthe-
sized and characterized by FTIR and magnetization
curve. The performance of MMWCNTs was evaluated
by adsorption of three chiral pesticides in lettuce, cab-
bage, and apple. The results showed that the three chiral
pesticides were enantioseparated under the HPLC‐UV
condition. Recoveries of pesticide residues in samples
were in the range of 73.4% to 110.9% with RSDr less than
7.6% (n = 5). The LOQs of the target pesticide residues
obtained by this method were in the range of 0.10 to
0.25 mg·kg−1. It demonstrates that MMWCNTs have the
advantages of high extraction efficiency, convenient oper-
ation, low cost, and short time consuming as a new type
of material. Based on these superiorities, this research
FIGURE 7 Comparison of absorbability between magnetic
multiwalled carbon nanotubes and multiwalled carbon nanotubes
(M: Metalaxyl, T: Tebuconazole, and E: Epoxiconazole)

8
LEI ET AL.
10. Mastovska K, Dorweiler KJ, Lehotay SJ, Wegscheid JS, Szpylka
KA. Pesticide multiresidue analysis in cereal grains using modi-
fied QuEChERS method combined with automated direct
sample introduction GC‐TOFMS and UPLC‐MS/MS techniques.
J Agric Food Chem. 2010;58(10):5959‐5972.
provides a novel method to extract pesticides in fruits and
vegetables. What is more, this study combined this with
chiral liquid chromatography, providing a method basis
for further research on chiral pesticides in foods.
11. Bidari A, Ganjali MR, Norouzi P, Hosseini MR, Assadi Y.
Sample preparation method for the analysis of some organo-
phosphorus pesticides residues in tomato by ultrasound‐
assisted solvent extraction followed by dispersive liquid‐liquid
microextraction. Food Chem. 2011;126(4):1840‐1844.
ACKNOWLEDGMENTS
This work was supported by the National Natural Science
Foundation of China (No. 81503029) and Shenyang
Pharmaceutical University (ZQN2016011).
12. Rodríguez‐Sanmartín P, Moreda‐Piñeiro A, Bermejo‐Barrera A,
Bermejo‐Barrera P. Ultrasound‐assisted solvent extraction of total
polycyclic aromatic hydrocarbons from mussels followed by
spectrofluorimetric determination. Talanta. 2005;66(3):683‐690.
ORCID
Longshan Zhao http://orcid.org/0000-0001-5330-0689
13. Lamas JP, Sanchezprado L, Garciajares C, Llompart M.
Determination of fragrance allergens in indoor air by active
sampling followed by ultrasound‐assisted solvent extraction
and gas chromatography‐mass spectrometry. J Chromatogr A.
2010;1217(12):1882‐1890.
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