Imidazolium ionic-liquid-modified phenolic resin for solid-phase extraction of thidiazuron and forchlorfenuron from cucumbers

Journal of Chromatography A 1623 (2020) 461192

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Journal of Chromatography A
journal homepage: www.elsevier.com/locate/chroma

Imidazolium ionic-liquid-modified phenolic resin for solid-phase
extraction of thidiazuron and forchlorfenuron from cucumbers
Pengfei Li a, Yanke Lu a, Jiangxue Cao a, Mengyuan Li a, Chunliu Yang a,∗, Hongyuan Yan a,b,∗
a
b

Key Laboratory of Medicinal Chemistry and Molecular Diagnosis, College of Public Health, Hebei University, Baoding, 071002, China
Key Laboratory of Analytical Science and Technology of Hebei Province, College of Pharmaceutical Science, Hebei University, Baoding, 071002, China

a r t i c l e

i n f o

Article history:
Received 21 February 2020
Revised 30 April 2020
Accepted 30 April 2020
Available online 5 May 2020
Keywords:
Imidazolium ionic liquid
Phenolic resin
Solid-phase extraction
Benzoylurea plant hormone
Cucumber

a b s t r a c t
An imidazolium ionic-liquid-modified phenolic resin (ILPR) was synthesized using 3-aminophenol as a
functional monomer, glyoxylic acid as a green cross-linker, and polyethylene glycol 60 0 0 as a porogen.
The obtained ILPR showed better extraction of benzoylurea plant hormones thidiazuron and forchlorfenuron than the unmodified phenolic resin because the imidazolium IL provides more interaction modes
with the analytes. ILPR, as a tailored adsorbent for solid-phase extraction, was coupled with highperformance liquid chromatography (ILPR–SPE–HPLC) for the simultaneous determination of thidiazuron
and forchlorfenuron in cucumbers. Good linearity of the ILPR–SPE–HPLC method was obtained, ranging
from 0.0100 to 5.00 μg g−1 with a correlation coefficient (r) ≥ 0.9999. The recoveries of spiked samples
ranged from 91.4% to 100.7% with a relative standard deviation of ≤ 6.0%.

1. Introduction
Widely used in crop production in many countries, thidiazuron
(TDZ) and forchlorfenuron (CPPU) are benzoylurea plant hormones
that regulate plant growth and development and promote fruit
quality [1–4]. However, several studies have shown that they may
interfere with the endocrine system and could be harmful to human genes [5]. Since the maximum residue limits (MRLs) for
TDZ and CPPU in fruits and vegetables are strictly controlled at
50 μg kg−1 in many countries [6], there is an urgent need to develop sensitive, accurate methods to detect trace levels of these
compounds. To date, a number of methods have been developed
based on liquid chromatography [7,8], liquid chromatographytandem mass spectrometry [9–11], gel chromatography-gas chromatography/mass spectrometry [12], Raman spectroscopy [6], ion
mobility spectrometry [13], and electrophoresis [14,15]. Although
these methods have their own advantages, all suffer from impurity
interference due to the complex sample matrices [16]. Therefore, a
simple and effective sample pretreatment method would be very
desirable for complicated samples before instrumental analysis.
Solid-phase micro-extraction, solid-phase extraction (SPE), magnetic solid-phase extraction, and matrix solid-phase dispersion

∗

Corresponding authors.

E-mail addresses: (C. Yang), (H. Yan).

/>0021-9673/© 2020 Elsevier B.V. All rights reserved.

© 2020 Elsevier B.V. All rights reserved.

[17–24] are the most widely used pretreatment techniques because
they not only separate and purify simultaneously, but also are economical, simple, and fast [25,26]. In a sense, it is crucial to develop new adsorbents with higher adsorption selectivities and excellent adsorption capacities, which can improve the efficiencies of
these methods [17,21]. In recent years, phenolic resins have been
used in the field of separation science owing to their high porosity,
excellent thermal stability, and low cost of raw materials [27–29].
However, the reported traditional phenolic resins function through
a single type of adsorption interaction. Furthermore, the formaldehyde used as the cross-linker in the preparation of those phenolic resins is harmful to the environment and human health; it can
induce respiratory irritation, allergic reaction, and cancer, even at
concentrations slightly higher than nature levels [29,30]. It would
be desirable to develop innovative resin adsorbents with high adsorption capacity, multiple adsoption interactions, and green synthesis process. To this end, we considered the use of glyoxylic acid
(H(CO)CO2 H), a biodegradable, natural component of plants, which
could serve as a cross-linking agent.
Ionic liquids (ILs) are molten salts consisting of inorganic anions and organic cations [31]. Generally low in toxicity, recyclable, and functionalizable [32], they have been widely used
in the extraction and separation fields [16,33–36]. The ILs used
in adsorbent synthesis are expected to participate in multiple
types of molecular interactions [37,38], which would not only
improve the adsorption selectivity for the desired adsorbent but


2

P. Li, Y. Lu and J. Cao et al. / Journal of Chromatography A 1623 (2020) 461192

also increase its adsorption capacity. Du et al. synthesized imidazolium IL-functionalized poly(ethylene glycol dimethacrylate-covinylimidazole) microspheres that showed excellent adsorption capacity for thymopentin [39]. Hence, we expected that modification

of a resin adsorbent with an imidazolium IL would enrich its adsorption interactions and improve its adsorption capacity.
In this work, glyoxylic acid as a green cross-linker was employed to synthesize an imidazolium IL-modified phenolic resin
(ILPR), avoiding the use of the highly toxic formaldehyde crosslinker in the preparation of a traditional phenolic resin. We then
applied the obtained ILPR as a tailored SPE adsorbent, coupling it
with HPLC (ILPR–SPE–HPLC) to extract and detect trace TDZ and
CPPU in cucumbers. The ILPR–SPE–HPLC method combined the advantages of the multiple interactions of the IL, high hydrophilicity
and porosity of the phenolic resin, and the economy and simplicity of SPE, and was applied for the extraction and determination of
TDZ and CPPU in foodstuff samples.
2. Experimental
2.1. Chemicals and reagents
Acetic acid was obtained from Tianjin Guangfu Fine Chemical
Co., Ltd. TDZ, CPPU, glyoxylic acid, and 1-chlorohexane were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.
Polyethylene glycol 60 0 0 (PEG 60 0 0), trifluoroacetic acid, and imidazole were purchased from Tianjin Kemiou Chemical Reagent Co.,
Ltd. Ethyl acetate was obtained from Tianjin Beichen Reagent Factory. 3-Aminophenol and 2-bromoethanol were obtained from Beijing J&K Scientific Co., Ltd. Ultra-pure water was filtered through a
membrane filter (0.45 μm) before use.
2.2. Instruments and conditions
Fourier-transform infrared spectra (FT-IR) of the ILPR were obtained with a Vertex70 FTIR spectrometer (Bruker, Karlsruhe, Germany). Elementary analyses were performed on Thermo Flash
20 0 0 elementary analyzer (Thermo Fisher Scientific, USA). Bromine
(Br) element analysis was performed on IC20 0 0 ion chromatograph (Dionex, USA). The 13 C nuclear magnetic resonance (NMR)
spectra was recorded on a Bruker AVANCE III 400 WB spectrometer (Bruker, Germany). The surface morphology of the
ILPR was investigated by scanning electron microscopy (Phenom Pro, Eindhoven, Netherlands). The chromatographic system
employed was an UltiMate-30 0 0 liquid chromatograph (Thermo
Fisher Scientific, USA) equipped with an Eclipse Plus C18 column
(4.6 mm × 150 mm, 3.5 μm), Chromeleon 7.2 workstation, and
UV detector with a wavelength of 278 nm. The mobile phase was
water–acetonitrile (60:40, v/v, with 0.1% trifluoroacetic acid) with
a flow rate of 1.0 mL min−1 . The injection volume was 20 μL, and
the column temperature was set at 25 °C.
2.3. Preparation of imidazolium ionic-liquid-modified phenolic resin
Imidazole (6.80 g) and 1-chlorohexane (6.00 g) were mixed in

ethyl acetate (40 mL) in a 100 mL flask and stirred for 72 h at
70 °C. The product was washed three times with water (10 mL)
to remove unreacted reagents. The ethyl acetate was then removed
at 35 °C using a rotary evaporator. The residue was subsequently
vacuum-dried at 50 °C until a constant weight was obtained. Then,
this material (1.50 g) and 2-bromoethanol (1.50 g) were mixed
with ethyl acetate (20 mL) in a hydrothermal kettle and reacted
at 120 °C for 5 h. After cooling to room temperature, the bottom
IL layer was removed.
3-Aminophenol (0.327 g), PEG 60 0 0 (0.30 0 g), and the IL
(0.828 g) were added to flask A with acetonitrile (20 mL) and

stirred until a clear solution was formed. Then, concentrated sulfuric acid (1.5 mL) was added to flask A. Glyoxylic acid (0.653 g)
was dissolved in acetonitrile (20 mL) in flask B. The contents of
flask A were mixed with B and the mixture was stirred at 45 °C
for 30 min; thereafter, the temperature was increased to 75 °C for
24 h. After washing the cooled reaction mixture with ethanol and
deionized water, the residue was vacuum-dried to obtain the ILPR.
The phenolic resin without IL modification (PR) was synthesized
using an identical method, except for the addition of the IL and
H2 SO4 .
2.4. ILPR–SPE process
The ILPR (20.0 mg) was placed into an empty SPE column
(6 cm × 1 cm) between two polyethylene screen plates. Then,
the ILPR column was activated with methanol (2.0 mL) followed
by water (2.0 mL). Subsequently, the sample solution (1.0 mL)
was loaded and the column was washed with water (1.0 mL) and
eluted with methanol/acetic acid (9:1 v/v, 1.5 mL). The eluate was
collected and evaporated to dryness under a nitrogen stream and
redissolved with the mobile phase (0.50 mL) for HPLC. To achieve

full extraction of the analytes by the adsorbent, combined with the
absorption amount of ILPR and the flow rate of other literature
[6,21], the flow rate was set to two drops per minute. To control
the flow rate at this level, a rubber bulb with an iron frame was
used during the SPE process. Briefly, the tip of the rubber bulb was
tightly inserted into the SPE column, while the head was clamped
using a clip, and the flow rate was adjusted by controlling the force
of the clip.
2.5. Preparation of cucumber samples
Cucumber samples (25.0 g) obtained from the farmers’ markets in Baoding were homogenized using a homogenizer, and the
solid residues were precipitated by centrifugation at 150 0 0 rpm
for 15 min. To precipitate the sample matrix, the juice was mixed
twice with lead acetate solution (16 wt%, 1.5 and 0.50 mL portions). The sample was then centrifuged and the supernatant was
freeze-dried overnight. The residue was dissolved in methanol
(20 mL), passed through a 0.45 μm membrane, and evaporated
to dryness. Finally, the mixture was redissolved with doubledeionized water (20 mL) for HPLC.
3. Results and discussion
3.1. Characteristics of the ILPR and PR
A schematic illustrations of the ILPR synthesis is shown in
Fig. 1. The glyoxylic acid crosslinker and imidazolium IL were
condensed by an esterification reaction, and the IL-modified
crosslinker was reacted with the 3-aminophenol monomer to form
the ILPR. The positively charged imidazole ring was introduced in
the ILPR by modifying the IL, which increased its electrostatic attraction to the analytes and improved the adsorption capacity. The
amounts of TDZ and CPPU adsorbed by the ILPR are obviously
higher than those of the unmodified PR (Fig. 2A). The ILPR adsorbs
a larger amount of CPPU than TDZ, which may be due to the electrostatic interaction between the positive charge carried on the IL
and the electronegative chlorine atom on CPPU, which promotes its
adsorption. Hydrogen bonding also plays an important role.
The SEM images in Fig. 2C and D reveal obvious differences

between the ILPR and PR. The morphology of PR is revealed as
stacked microparticles that are approximately spherical. In contrast, the ILPR presents a fluffy porous structure with a rough surface and tiny through pores, which are mainly ascribed to the


P. Li, Y. Lu and J. Cao et al. / Journal of Chromatography A 1623 (2020) 461192

3

Fig. 1. Schematic illustration of the ILPR synthesis route.

sticky imidazolium IL. Compared with PR, the ILPR adsorbent exhibits excellent features, including a rough surface that provids
numerous binding sites which should be beneficial for interaction
with the target molecules. In addition, the tiny through pores in
the ILPR could reduce the mass transfer resistance of the analytes,
which should be conducive to rapid extraction.
The FT-IR spectra of the ILPR and PR are shown in Fig. 2B.
A broad peak corresponding to the O–H stretching vibration is
observed at 3397 cm−1 . The adsorption band at 2920 cm−1 is
due to the asymmetric stretching vibration of C–H, while that at
1718 cm−1 is attributed to the C=O stretching vibration of glyoxylic acid. A peak corresponding to the C=C vibrations of 3aminophenol appears at 1629 cm−1 . Typically, the peaks at 1082
and 837 cm−1 are ascribed to the symmetric stretching vibrations
of the imidazole ring and C–H of the aromatic ring. These results
indicate that the IL was successfully introduced into the PR, which
would enable the generation of hydrogen bonds and electrostatic
interactions between the adsorbent and analytes.
The obtained ILPR was confirmed by 13 C NMR, as shown in
Fig. 2E, the major signals are carboxylic ester (δ in 173.97 ppm),
aromatic ring (δ in around 100 and 121 ppm), imidazole ring (δ
in around 137 ppm), alkyl (δ in around 50 ppm), and ether (δ in
70.75 ppm). These results are consistent with the results of FT-IR,

indicating that the IL was successfully introduced into the PR. Elemental analysis was used to characterize the elemental composition of the ILPR. The results show that ILPR is primarily composed
of C (54.21%), O (28.45%). In addition, trace amount of Br (0.17%)
is detected, indicating that the IL was successfully introduced into
the PR.
3.2. Adsorption performance of the ILPR
The adsorption thermodynamics of the new adsorbent was
studied by mixing ILPR (5.00 mg) with various concentrations
of sample solution (2.0 mL; 5.00, 10.0, 20.0, 30.0, 40.0, 60.0, or
80.0 μg mL−1 ) at different temperatures. After shaking for 12 h
and centrifuging, the supernatants were analyzed by HPLC. The
isotherms for TDZ and CPPU adsorption at different temperatures
are presented in Fig. 3A and B, which show that the amounts of

TDZ and CPPU adsorbed on the ILPR increase with increasing initial analyte concentration at the same temperature. Moreover, the
adsorption capacity of the ILPR decreases with increasing temperature, suggesting that adsorption occurs via an exothermic process.
To evaluate the adsorption mechanism of ILPR, the adsorption
kinetics was evaluated by mixing the ILPR (5.00 mg) and a standard solution of each analyte (2.0 mL; 40.0 μg mL−1 ) in a 10 mL
centrifuge tube, and then shaking at 350 rpm and 25 °C for 2, 5,
10, 30, 60, 120, or 180 min. The supernatants were analyzed by
HPLC, and the obtained adsorption data were fitted with various
kinetics models [21]. The adsorption amount was calculated using
Eq.(1), where ci (μg mL−1 ) represents the initial concentration, ce
(μg mL−1 ) represents the concentration of the standard solution
at equilibrium, and V (mL) and W (g) represent the solution volume and weight of the sorbent, respectively. As shown in Eqs.(2)
and (3), k1 (min−1 ) and k2 (g mg−1 min−1 ) represent pseudo-firstorder and pseudo-second-order rate constants, respectively, and Qe
(mg g−1 ) and Qt (mg g−1 ) are the adsorption capacities of ILPR for
TDZ and CPPU at equilibrium and time t, respectively.

Qe =

(Ci − Ce ) × V
W

(1)

ln(Qe − Qt ) = lnQe − k1 t

(2)

t
1
t
=
+
Qt
Qe
K2 Qe 2

(3)

The linear fittings of the kinetics models are shown in Fig. 3C
and D, and the data are listed in Table 1. The R2 value of the
quasi-second-order equation is obviously higher than that of the
other, indicating that the process of adsorption by ILPR may operate via chemisorption or strong surface complexation rather than
mass transfer [21].
3.3. Optimization of ILPR-SPE process
The parameters affecting the extraction performance of the
ILPR-SPE, including the sample loading volume, and type and volume of washing solvent and eluent, were next optimized. As

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P. Li, Y. Lu and J. Cao et al. / Journal of Chromatography A 1623 (2020) 461192

Fig. 2. Absorption amounts (A), FT-IR spectra (B), and SEM images of PR (C) and ILPR (D), and

13

C NMR spectra of ILPR (E).

Table 1
Kinetic parameters for ILPR.
Pseudo-first order
Analytes Qe,cal (μg mg−1 )
k1 (min−1 )

R2

Pseudo-second order
Qe,cal (μg mg−1 )
k2 (g mg−1 min−1 )

R2

TDZ
CPPU

0.9675
0.9493

7.4985
11.7495

0.9909
0.9911

3.3242
4.6886

0.0071
0.0076

shown in Fig. 4A, the recovery of analytes decreases as the loading
volume of the sample increases, which is due to the large loading
volume breaking through the adsorption amount of the adsorbent.
Therefore, 1.0 mL of loading solution was selected for further processing.
The washing solvent plays a critical role in the removal of coadsorbed interferents during the extraction process, while ensuring that the adsorption interaction between the analytes and ad-

0.0221
0.0150

sorbent is not destroyed. In this work, five washing solvents were
investigated, with water providing the lowest loss rate of TDZ and
CPPU (Fig. 4B). From the perspective of the purification effects,
most of the interfering substances originating from the sample matrix are washed out from the SPE column effectively. After optimization, the washing solvent was established as 1.0 mL water.
As demonstrated in Fig. 4C, five elution solvent systems were
investigated, with methanol/acetic acid (9:1 v/v) exhibiting the


P. Li, Y. Lu and J. Cao et al. / Journal of Chromatography A 1623 (2020) 461192

5

Fig. 3. Amounts of TDZ (A) and CPPU (B) adsorbed by ILPR, and kinetics plots for the pseudo-first order (C) and pseudo-second order rate equations for ILPR (D).

Table 2
Parameters for the ILPR–SPE–HPLC method.
Analyte

Linearity (μg g−1 )

Correlation coefficient (r)

Calibration plot (y = ax+b)

LOD (μg g−1 )

LOQ (μg g−1 )

RSD (%) Intra-day

Inter-day

TDZ
CPPU

0.0100–5.00
0.0100–5.00

0.9999

0.9999

y = 1.3967x+0.0006
y = 1.6596x−0.0162

0.00195
0.00169

0.00651
0.00564

1.32
0.66

4.41
4.73

Table 3
Spiked recoveries for the ILPR–SPE–HPLC method.
0.0500 (μg g−1 )
Analyte Recovery (%)
RSD (%)

1.00 (μg g−1 )
Recovery (%)

RSD (%)

5.00 (μg g−1 )
Recovery (%)

RSD (%)

TDZ
CPPU

95.1
100.7

5.4
4.6

91.4
98.1

0.9
0.2

91.4
96.1

6.0
2.4

highest recovery. Because TDZ and CPPU are protonated under
acidic conditions, the electrostatic attraction and hydrogen bonding
interactions with the ILPR are weakened. After volume optimization, 1.5 mL methanol/acetic acid (9:1 v/v) was used for further
investigations.
3.4. Validation of the ILPR–SPE–HPLC method
The ILPR–SPE–HPLC method was validated in terms of its linearity, limit of detection (LOD), limit of quantitation (LOQ), precision,

accuracy, and spiked recovery. Calibration curves were obtained using nine spiked levels of TDZ and CPPU in the range of 0.0100–
5.00 μg g−1 , with correlation coefficients (r) of ≥0.9999 (Table 2).
The LODs and LOQs, calculated according to LOD = 3 Sb/m and
LOQ = 10 Sb/m (where m is the calibration slope and Sb is the

standard deviation [40]), were 0.00195 and 0.00169 μg g−1 , and
0.0 0651 and 0.0 0564 μg g−1 for TDZ and CPPU, respectively. The
accuracy and precision of the method were evaluated by performing three replicate measurements (5.00 μg mL−1 ) on the same day
(n = 3) and three consecutive days, while their intra-day and interday precisions expressed as relative standard deviations (RSDs) are
in the ranges 0.66–1.32% and 4.41–4.73% for TDZ and CPPU, respectively. Finally, the recoveries are 91.4–100.7% (RSD ≤ 6.0%)
(Table 3), which were determined at three spiked levels (0.0500,
1.00, and 5.00 μg g−1 ).
3.5. Detection of TDZ and CPPU in cucumber samples
The feasibility of the ILPR–SPE–HPLC method was evaluated using five cucumber samples obtained from the farmers’ markets


6

P. Li, Y. Lu and J. Cao et al. / Journal of Chromatography A 1623 (2020) 461192

Fig. 4. Optimization of ILPR–SPE procedure. (A: Loading volume, B: washing solvent; C and D: elution solvents).

Table 4
Comparison of the present method with reported methods.
Method
SPE
SPE
DLLME
QuEChERS
QuEChERS

SPE
SPE

Detection
SERS
HPLC
HPLC-DAD
LC–MS/MS
LC–MS/MS
IMS
HPLC

Sample
Grapes, kiwi
Grapes, pitaya
River water
Grapes
Fruits
Fruit juices
Cucumber

Absorbent (mg)
100
100
—
—
—
150
20.0

Linearity

Recovery (%)
−1

30.0–300 ng mL
30.0–200 × 103 ng g−1
1.00–100 ng mL−1
0.100–50.0/1.00–500 ng mL−1
5.00–500 ng mL−1
10.0–400 ng mL−1
10.0–5.00 × 103 ng g−1

78.9–87.9
72.4–94.9
91–101
75.6–109.0
79.9–109.1
80–115
91.4–100.7

LOD
−1

15.0 ng mL
16.1 ng g−1
0.500 ng mL−1
—
0.300–0.400 ng g−1
2.00 ng mL−1

1.69–1.95 ng g−1

RSD (%)

Ref.

8.1–13.2
0.18–3.53
6.4
1.2–11.4
1.1–10.4
7.6
0.2–6.0

[6]
[7]
[8]
[10]
[11]
[13]
This work

SERS: surface-enhanced raman spectroscopy; HPLC-DAD: HPLC-diode array detection; DLLME: dispersive liquid–liquid microextraction;
IMS: ion mobility spectrometry.

in Baoding, China. In one of the cucumbers, a trace of TDZ (i.e.,
43.5 ng g−1 ) was detected, which is below the maximum residue
limit (50.0 ng g−1 ). Fig. 5 shows that all interferences from the cucumber matrix were effectively removed and no impurity peaks
exist near the retention times of the analytes, indicating that the
proposed ILPR–SPE–HPLC method is an effective extraction and

isolation process for the accurate determination of trace levels of
TDZ and CPPU in cucumbers.

3.6. Method comparison with reference methods
A comparison of the present method with reported methods
is shown in Table 4. The developed ILPR–SPE–HPLC method uses
less absorbent, and further, affords a lower LOD compared to other
methods that use SPE as a pretreatment technique. Compared
with LC−MS/MS, the developed ILPR–SPE–HPLC method exhibits a
higher LOD, but the expensive instrumentation of the former lim-


P. Li, Y. Lu and J. Cao et al. / Journal of Chromatography A 1623 (2020) 461192

7

References

Fig. 5. Chromatograms of spiked sample (A) and cucumber-derived sample (B).

its its application for routine analysis. In addition, the recoveries
for TDZ and CPPU by the proposed method are similar to those
of the reference methods. Therefore, the proposed ILPR–SPE–HPLC
method could be employed for the analysis of trace CPPU and TDZ
in cucumbers.

4. Conclusion
In this work, a new type of ILPR employing glyoxylic acid as
a green cross-linker was prepared and used as a special SPE adsorbent for the extraction of TDZ and CPPU from cucumbers. Due
to hydrogen bonding and electrostatic interactions, the ILPR obviously increased the extraction efficiency and adsorption capacity compared to the unmodified PR. The developed ILPR–SPE–HPLC

method was employed to successfully extract and detect TDZ and
CPPU in cucumber. Therefore, the ILPR can serve as a potential SPE
adsorbent and is expected to be used for the separation and determination of benzoylurea plant hormones in cucumber samples.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to
influence the work reported in this paper.

CRediT authorship contribution statement
Pengfei Li: Methodology, Conceptualization. Yanke Lu: Data
curation, Validation. Jiangxue Cao: Software, Formal analysis.
Mengyuan Li: Writing - review & editing. Chunliu Yang: Visualization, Project administration. Hongyuan Yan: Conceptualization,
Methodology, Supervision.

Acknowledgments
This work is supported by the Natural Science Foundation of
Hebei Province (B2018201270, H2019201288), the National Natural Science Foundation of China (21575033), the Talent Engineering Training Foundation of Hebei Province (A201802002), and
the Post-graduate’s Innovation Fund Project of Hebei University
(hbu2019ss073, hbu2020ss004) .

[1] A. Valverde, A. Aguilera, C. Ferrer, F. Camacho, A. Cammarano, Analysis of
forchlorfenuron in vegetables by LC/TOF-MS after extraction with the buffered
QuEChERS method, J. Agric. Food Chem. 58 (2010) 2818–2823, doi:10.1021/
jf904465s.
[2] J. Fenoll, P. Hellín, C.M. Martínez, P. Flores, S. Navarro, High performance liquid
chromatography-tandem mass spectrometry method for quantifying phenylurea herbicides and their main metabolites in amended and unamended soils,
J. Chromatogr. A 1257 (2012) 81–88, doi:10.1016/j.chroma.2012.08.014.
[3] N Campillo, P Viđas, G Férez-Melgarejo, M Hernández-Córdoba, Dispersive
liquid-liquid microextraction for the determination of three cytokinin compounds in fruits and vegetables by liquid chromatography with time-of-flight
mass spectrometry, Talanta 116 (2013) 376–381, doi:10.1016/j.talanta.2013.05.

063.
[4] K. Matsumoto, T. Fujita, S. Sato, Exogenous applications of plant growth regulators improve quality of ‘Fuji’Apple, Int. J. Agric. Biol. 20 (2018) 2083–2090,
doi:10.17957/IJAB/15.0 0 0 0.
[5] C. Tixier, M. Sancelme, M. Sancelme, F. Bonnemoy, A. Cuer, H. Veschambre,
Degradation products of a phenylurea herbicide, diuron: synthesis, ecotoxicity,
and biotransformation, Environ. Toxicol. Chem. 20 (2001) 1381–1389, doi:10.
10 02/etc.562020 0701.
[6] X. Chen, K. Yan, X. Xiao, G. Li, Analysis of forchlorfenuron and thidiazuron
in fruits and vegetables by surface-enhanced Raman spectroscopy after selective solid-phase extraction with modified β -cyclodextrin, J. Sep. Sci. 39 (2016)
2340–2346, doi:10.10 02/jssc.20160 020 0.
[7] F. Wang, W. Zhang, Y. Chen, G. Xu, Z. Deng, H. Du, W. Zhao, S. Zhang, W. Zhao,
Simultaneous determination of six plant growth regulators in fruits using
high performance liquid chromatography based on solid-phase extraction and
cleanup with a novel mixed-mode functionalized calixarene sorbent, Anal.
Methods 7 (2015) 6365–6371, doi:10.1039/C5AY01167A.
[8] M. Saraji, N. Tansazan, Application of dispersive liquid-liquid microextraction for the determination of phenylurea herbicides in water samples by
HPLC-diode array detection, J. Sep. Sci. 32 (2009) 4186–4192, doi:10.1002/jssc.
20 090 0438.
[9] J.Y. Park, J.H. Choi, A.A. El-Aty, B.M. Kim, J.H. Oh, J.A. Do, K.S. Kwon, K.H. Shim,
O.J. Choi, S.C. Shin, J.H. Shim, Simultaneous multiresidue analysis of 41 pesticide residues in cooked foodstuff using QuEChERS: comparison with classical
method, Food Chem. 128 (2011) 241–253, doi:10.1016/j.foodchem.2011.02.065.
[10] C.H. Pu, S.K. Lin, W.C. Chuang, T.H. Shyu, Modified QuEChERS method for 24
plant growth regulators in grapes using LC-MS/MS, J. Food Drug Anal. 26
(2018) 637–648, doi:10.1016/j.jfda.2017.08.001.
[11] X. Shi, F. Jin, Y. Huang, X. Du, C. Li, M. Wang, H. Shao, M. Jin, J. Wang, Simultaneous determination of five plant growth regulators in fruits by modified
quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction and liquid
chromatography-tandem mass spectrometry, J. Agric. Food Chem. 60 (2012)
60–65, doi:10.1021/jf204183d.
[12] D. Lu, X. Qiu, C. Feng, Y. Lin, L. Xiong, Y. Wen, D. Wang, G. Wang, Simultaneous determination of 45 pesticides in fruit and vegetable using an improved QuEChERS method and on-line gel permeation chromatography-gas
chromatography/mass spectrometer, J. Chromatogr. B 895 (2012) 17–24, doi:10.

1016/j.jchromb.2012.03.006.
[13] A. Orellana-Silla, S. Armenta, M. de la Guardia, J.V. Mercader, F.A. EsteveTurrillas, Development of immunosorbents for the analysis of forchlorfenuron
in fruit juices by ion mobility spectrometry, Anal. Bioanal. Chem. 410 (2018)
5961–5967, doi:10.10 07/s0 0216- 018- 1213- 5.
[14] L. Yang, Y. Chen, S. Zhao, W. Zhang, H. Du, Z. Deng, S. Zhang, Simultaneous determination of indole-3-acetic acid and indole-3-butyric acid in plant by fieldamplified sample stacking open-tubular capillary electrochromatography based
on solid-phase extraction with calixarene sorbent, Chromatographia 79 (2016)
243–254, doi:10.1007/s10337-015-2999-3.
[15] Y. Chen, X. Wu, Y. Li, Y. Yang, D. Yang, S. Yin, L. Liu, C. Sun, Simultaneous determination of seven plant growth regulators in melons and fruits by modified QuEChERS coupled with capillary electrophoresis, Food Anal. Methods 11
(2018) 2788–2798, doi:10.1007/s12161- 018- 1266- 2.
[16] Y. Yuan, S. Liang, H. Yan, Z. Ma, Y. Liu, Ionic liquid-molecularly imprinted
polymers for pipette tip solid-phase extraction of (Z)-3-(chloromethylene)-6flourothiochroman-4-one in urine, J. Chromatogr. A 1408 (2015) 49–55, doi:10.
1016/j.chroma.2015.07.028.
[17] Y. Han, C. Yang, Y. Zhou, D. Han, H. Yan, Ionic liquid-hybrid molecularly imprinted material-filter solid-phase extraction coupled with HPLC for determination of 6-benzyladenine and 4-chlorophenoxyacetic acid in bean sprouts, J.
Agric. Food Chem. 65 (2017) 1750–1757, doi:10.1021/acs.jafc.6b03922.
[18] J. Zhang, W. Li, W. Zhu, P. Qin, M. Lu, X. Zhang, Y. Miao, Z. Cai, Mesoporous
graphitic carbon nitride@NiCo2 O4 nanocomposite as a solid phase microextraction coating for sensitive determination of environmental pollutants in human serum samples, Chem. Commun. 55 (2019) 10019–10 022 10 019-10 022,
doi:10.1039/C9CC04348A.
[19] G. Moreno-Martin, J. Sanz-Landaluze, M.E. León-Gonzalez, Y. Madrid, In-vivo
solid phase microextraction for quantitative analysis of volatile organoselenium compounds in plants, Anal. Chim. Acta 1081 (2019) 72–80, doi:10.1016/j.
aca.2019.06.061.
[20] M. Yu, L. Wu, J. Miao, W. Wei, A. Liu, S. Liu, Titanium dioxide and polypyrrole
molecularly imprinted polymer nanocomposites based electrochemical sensor
for highly selective detection of p-nonylphenol, Anal. Chim. Acta 1080 (2019)
84–94, doi:10.1016/j.aca.2019.06.053.


8

P. Li, Y. Lu and J. Cao et al. / Journal of Chromatography A 1623 (2020) 461192

[21] Y. Xie, M. Wang, X. Chen, S. Wang, D. Han, Y. Han, H. Yan, 3-Aminophenolglyoxylic acid resin for the determination of triazine herbicides in tomatoes,
Anal. Chim. Acta 1061 (2019) 122–133, doi:10.1016/j.aca.2019.01.062.
[22] H. Zhang, Y. Yuan, Y. Sun, C. Niu, F. Qiao, H. Yan, An ionic liquid-magnetic
graphene composite for magnet dispersive solid-phase extraction of triazine
herbicides in surface water followed by high performance liquid chromatography, Analyst 143 (2018) 175–181, doi:10.1039/C7AN01290J.
[23] Y. Sun, J. Tian, L. Wang, H. Yan, F. Qiao, X. Qiao, One pot synthesis of magnetic
graphene/carbon nanotube composites as magnetic dispersive solid-phase extraction adsorbent for rapid determination of oxytetracycline in sewage water,
J. Chromatogr. A 1422 (2015) 53–59, doi:10.1016/j.chroma.2015.10.035.
[24] T. Liang, L. Gao, D. Qin, L. Chen, Determination of sulfonylurea herbicides in
grain samples by matrix solid-phase dispersion with mesoporous structured
molecularly imprinted polymer, Food Anal. Methods 12 (2019) 1938–1948,
doi:10.1007/s12161- 019- 01539- y.
[25] L. Zhang, S. Liu, X. Cui, C. Pan, A. Zhang, F. Chen, A review of sample preparation methods for the pesticide residue analysis in foods, Cent. Eur. J. Chem. 10
(2012) 900–925, doi:10.2478/s11532- 012- 0034- 1.
[26] H. Yan, C. Yang, Y. Sun, K.H. Row, Ionic liquid molecularly imprinted polymers for application in pipette-tip solid-phase extraction coupled with gas
chromatography for rapid screening of dicofol in celery, J. Chromatogr. A 1361
(2014) 53–59, doi:10.1016/j.chroma.2014.07.102.
[27] M. Wang, S. Liang, L. Bai, F. Qiao, H. Yan, Green protocol for the preparation of
hydrophilic molecularly imprinted resin in water for the efficient selective extraction and determination of plant hormones from bean sprouts, Anal. Chim.
Acta 1064 (2019) 47–55, doi:10.1016/j.aca.2019.03.025.
[28] G. Ming, H. Duan, X. Meng, G. Sun, W. Sun, Y. Liu, L. Lucia, A novel fabrication
of monodisperse melamine-formaldehyde resin microspheres to adsorb lead
(II), Chem. Eng. J. 288 (2016) 745–757, doi:10.1016/j.cej.2015.12.007.
[29] M. Wang, H. Nie, D. Han, X. Qiao, H. Yan, S. Shen, Cauliflower-like resin microspheres with tuneable surface roughness as solid-phase extraction adsorbent
for efficient extraction and determination of plant growth regulators in cucumbers, Food Chem. 295 (2019) 259–266, doi:10.1016/j.foodchem.2019.05.130.
[30] C.J. Na, M.J. Yoo, D.C. Tsang, H.W. Kim, K.H. Kim, High-performance materials for effective sorptive removal of formaldehyde in air, J. Hazard. Mater. 366
(2019) 452–465, doi:10.1016/j.jhazmat.2018.12.011.

[31] X. Gao, M. Pan, G. Fang, W. Jing, S. He, S. Wang, An ionic liquid modified
dummy molecularly imprinted polymer as a solid-phase extraction material

for the simultaneous determination of nine organochlorine pesticides in environmental and food samples, Anal. Methods 5 (2013) 6128–6134, doi:10.1039/
c3ay41083h.
[32] Z. Radai, N.Z. Kiss, G. Keglevich, An overview of the applications of ionic liquids
as catalysts and additives in organic chemical reactions, Curr. Org. Chem. 22
(2018) 533–556, doi:10.2174/1385272822666171227152013.
[33] M. Mohamedali, H. Ibrahim, A. Henni, Incorporation of acetate-based ionic liquids into a zeolitic imidazolate framework (ZIF-8) as efficient sorbents for carbon dioxide capture, Chem. Eng. J. 334 (2018) 817–828, doi:10.1016/j.cej.2017.
10.104.
[34] H. Yan, M. Gao, J. Qiao, New ionic liquid modified polymeric microspheres for
solid-phase extraction of four Sudan dyes in foodstuff samples, J. Agric. Food
Chem. 60 (2012) 6907–6912, doi:10.1021/jf301224t.
[35] X. Wei, Y. Wang, J. Chen, R. Ni, J. Meng, Z. Liu, F. Xu, Y. Zhou, Ionic liquids skeleton typed magnetic core-shell molecularly imprinted polymers for
the specific recognition of lysozyme, Anal. Chim. Acta 1081 (2019) 81–92,
doi:10.1016/j.aca.2019.07.025.
[36] J. Cao, Q. Jiang, R. Li, Q. Xu, H. Li, Nanofibers mat as sampling module of direct analysis in real time mass spectrometry for sensitive and high-throughput
screening of illegally adulterated sulfonylureas in antidiabetic health-care teas,
Talanta 203 (2019) 753–761, doi:10.1016/j.talanta.2019.06.066.
[37] T.D. Ho, C. Zhang, L.W. Hantao, J.L. Anderson, Ionic liquids in analytical chemistry: fundamentals, advances, and perspectives, Anal. Chem. 86 (2014) 262–
285, doi:10.1021/ac4035554.
[38] M. Zhang, X. Liang, S. Jiang, H. Qiu, Preparation and applications of surfaceconfined ionic-liquid stationary phases for liquid chromatography, TrAC Trends
Anal. Chem. 53 (2014) 60–72, doi:10.1016/j.trac.2013.09.011.
[39] C. Du, X. Hu, P. Guan, L. Guo, L. Qian, R. Song, J. Li, C. Wang, Water-compatible
surface-imprinted microspheres for high adsorption and selective recognition
of peptide drug from aqueous media, J. Mater. Chem. B 3 (2015) 3044–3053,
doi:10.1039/C4TB02030H.
[40] A. Shrivastava, V.B. Gupta, Methods for the determination of limit of detection
and limit of quantitation of the analytical methods, Chron. Young Sci. 2 (2011)
21–25, doi:10.4103/2229-5186.79345.