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Glyoxal-Urea-Formaldehyde Molecularly Imprinted Resin as Pipette Tip Solid-Phase Extraction Adsorbent for Selective Screening of Organochlorine Pesticides in Spinach Chen Yang, Tianwei Lv, Hongyuan Yan, Gaochan Wu, and Haonan Li J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b02762 • Publication Date (Web): 08 Oct 2015 Downloaded from http://pubs.acs.org on October 14, 2015
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Glyoxal-Urea-Formaldehyde Molecularly Imprinted Resin as
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Pipette Tip Solid-Phase Extraction Adsorbent for Selective
3
Screening of Organochlorine Pesticides in Spinach
4
Chen Yang1, Tianwei Lv1, Hongyuan Yan∗1,2, Gaochan Wu1, Haonan Li1 1
5
Key Laboratory of Pharmaceutical Quality Control of Hebei Province, Hebei University,
6
Baoding, 071002, China 2
7
Key Laboratory of Medicinal Chemistry and Molecular Diagnosis, Ministry of Education,
8 9
Hebei University, Baoding, 071002, China
ABSTRACT:
10
A new kind of glyoxal-urea-formaldehyde molecularly imprinted resin (GUF-MIR)
11
was synthesized by a glyoxal-urea-formaldehyde (GUF) gel imprinting method with 4,
12
4'-dichlorobenzhydrol as a dummy template. The obtained GUF-MIR was
13
characterized by scanning electron microscope (SEM) and Fourier transform infrared
14
spectroscopy (FT-IR), and applied as a selective adsorbent of miniaturized pipette tip
15
solid-phase extraction (PT-SPE) for the separation and extraction of three
16
organochlorine pesticides (dicofol (DCF), dichloro diphenyl dichloroethane (DDD),
17
and tetradifon) in spinach samples. The proposed pretreatment procedures of spinach
18
samples involved only 5.0 mg of GUF-MIR, 0.7 mL of MeOH–H2O (1:1, v/v)
19
(washing solvent), and 0.6 mL of cyclohexane‒ethyl acetate (9:1, v/v) (elution
20
solvent). In comparison with other adsorbents (such as silica gel, C18, NH2-silica gel,
21
and neutral alumina (Al2O3-N)), GUF-MIR showed higher adsorption and purification ∗
Corresponding author. Tel. /Fax: +86-312-5079788. E-mail address:
[email protected]. 1
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capacity for DCF, DDD, and tetradifon in aqueous solution. The average recoveries at
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three spiked levels ranged from 89.1% to 101.9% with relative standard deviations
24
(RSDs) ≤7.1% (n=3). The presented GUF-MIR-PT-SPE method combines the
25
advantages of molecularly imprinted polymers (MIPs), GUF, and PT-SPE, and can be
26
used in polar solutions with high affinity and selectivity to the analytes in complex
27
samples.
28
KEYWORDS: glyoxal-urea-formaldehyde gel, molecularly imprinted resin, pipette
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tip solid-phase extraction, organochlorine pesticides, spinach
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INTRODUCTION
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Organochlorine pesticides (OCPs) have been widely used because of their strong
32
effects in control of pests and diseases.1 There are several kinds of OCPs in nature
33
including a group of DCF, DDD, tetradifon, DDT and so on, of which the structures
34
are similar to 4, 4'-dichlorobenzhydrol. According to No. 199 Public Notice from the
35
Ministry of Agriculture of the People’s Republic of China, DDT is forbidden as a
36
pesticide in agriculture, but other OCPs such as DCF, DDD, and tetradifon are still
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commonly used in agriculture. Although the huge use of them makes great economic
38
profit, it has also caused serious environmental pollution, acute toxicity, and
39
bioaccumulation that are very harmful to wild animals and human beings.2‒4 Thus a
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selective, sensitive, and convenient method for determination of OCPs (DCF, DDD,
41
and tetradifon) in fruits and vegetables is imperative.
42 43
Until now, several analytical methods for determination of OCPs developed
including
liquid
chromatography–tandem 2
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mass
have been spectrometry
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(LC–MS/MS),5
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(HPLC‒UV),6 and gas chromatography–tandem mass spectrometry (GC–MS/MS).7,8
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Apart from occurring at low concentrations of analytes, the matrix interference of
47
complex real samples makes the analysis difficult. Therefore, it is necessary to
48
develop an appropriate sample pretreatment method for purifying and enriching OCPs
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(DCF, DDD, and tetradifon) prior to final instrumental analysis. Generally,
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solid-phase extraction (SPE),9 dispersive solid-phase extraction (DSPE),10 single-drop
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microextraction,11 supercritical fluid extraction (SFE),12 matrix solid-phase dispersion
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(MSPD),13 dispersive liquid–liquid microextraction (DLLME),14 microwave-assisted
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extraction
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microwave-assisted steam distillation (MASD),16 and stir-bar sorptive extraction
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(SBSE)17 are often employed for the extraction and purification of OCPs. Besides,
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generic extraction methods (such as QuEChERS, SPE, etc) are developed to extract
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target compounds simultaneously, but one obvious drawback is the occurrence of
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abundant interference components originating from sample matrices due to the low
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selectivity of the adsorbents, which compromise detection limits, quantitative aspects,
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and method selectivity.18 Among these methods, SPE is the most widely used for
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sample pretreatment. Recently, pipette tip-SPE (PT-SPE), as one efficient
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miniaturized format of SPE, has attracted great attention.19,20 The homemade micro tip
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has the advantages of small bed volume and sorbent mass, low solvent consumption,
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ease of operation, time efficiency, and versatility.21,22 However, the common
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adsorbents such as silica gel, C18, C8, NH2-silica gel, HLB, and Al2O3-N are limited
high-performance
coupled
with
gel
liquid
chromatography‒ultraviolet
permeation
chromatography
3
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detector
(MAE‒GPC),15
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owing to the lack of specific recognition to analytes in complex samples. Thus,
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adsorbents with selective affinity are desired greatly.
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In the last decade, the use of molecularly imprinted polymers (MIPs) in SPE have
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displayed high recognition ability to extract target analytes from complicated sample
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matrices.23‒26 However, we can’t overlook the inherent limitations of MIPs, one of
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which is their incompatibility with aqueous media restricting their further applications
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in biological and environmental aspects.27 GUF gel as a hydrophilic functional
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monomer can be introduced in the synthetic procedure of MIR, which can improve
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the compatibility with polar solutions and reduce the toxic reagent compared with UF
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gel.28‒31
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In this study, a new type of glyoxal-urea-formaldehyde molecularly imprinted resin
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(GUF-MIR) was fabricated with GUF gel as functional monomer and 4,
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4'-dichlorobenzhydrol as dummy template. GUF-MIR was employed as PT-SPE
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adsorbent for the rapid isolation of OCPs (DCF, DDD, and tetradifon) in five kinds of
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spinach. The proposed sample pretreatment method combining the advantages of
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MIPs, GUF, and PT-SPE could be used in aqueous matrices with high affinity and
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selectivity to the analytes in complex samples.
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EXPERIMENTAL PROCEDURES
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Chemicals and Reagents. DCF was purchased from Dacheng Pesticide Co., Ltd.
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(Shandong, China). DDD, tetradifon, formaldehyde, urea, and glyoxal were purchased
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from Kermel Chemical Co., Ltd. (Tianjin, China). 4, 4'-dichlorobenzhydrol was
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obtained from Tokyo Chemical Industry Co., Ltd (Japan). Tween 80 was purchased 4
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from Tianjin Guangfu Fine Chemical Research Institute (Tianjin, China).
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3-indolebutyric acid (ITA) and atrazine were obtained from Aladdin Reagent Co., Ltd.
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(Shanghai, China). Methanol (MeOH, HPLC grade), acetonitrile (ACN, HPLC grade),
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n-hexane, acetone, dichloromethane, toluene, and cyclohexane ethyl acetate were
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obtained from Kermel Chemical Co., Ltd. (Tianjin, China). Acetic acid glacial (HOAc)
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was obtained from Tianjin Guangfu Technology Development Co., Ltd. (Tianjin,
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China). The adsorbent materials of C18, silica gel, NH2-silica gel, and Al2O3-N were
95
purchased from Varian Co. (Palo Alto, CA, USA). Double-deionized water was
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filtered with a 0.45-µm filter membrane before use.
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Instrumentation and Conditions. GC analysis was performed on a GC-2014 gas
98
chromatography (Shimadzu, Japan) equipped with a split/splitless injector and an
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electron capture detector (ECD). A WM-5 capillary column (5% diphenyl‒
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dimethylpolysiloxane, 30 m × 0.25 mm × 0.25 µm) was obtained from Welch
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Materials Co., Ltd. (Shanghai, China). An N-2000 data workstation (Zheda Zhineng
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Co., Ltd., Hangzhou, China) was used as the data acquisition system. High purity
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nitrogen (99.999%) was employed as the carrier gas of GC. The injection port, oven
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temperature, and detector temperatures were set at 250 °C, 200 °C, and 290 °C
105
respectively with the column flow rate of 1.7 mL/min. FT-IR spectrometer
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(VERTEX70) was purchased from Germany Bruker Co., Ltd. (Germany) and
107
scanning electron microscope (SEM) KYKY-2800B (FEI Co., Hillsboro, USA) was
108
used for morphological evaluation.
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Synthesis of GUF-MIR. 4,4'-dichlorobenzhydrol (0.2776 g) was dissolved fully 5
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into Tween 80 (2.0 mL) by ultrasonic and stirring in a beaker, after which distilled
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water (80.0 mL), urea (4.5 g), formaldehyde (12.0 mL), and glyoxal (9.2 mL) were
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added successively with stirring. After standing for 1 h, acetic acid (0.4 mL) was
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added into the mixture and then the solution was sat for 4 h. The solid was collected
114
and washed with methanol‒acetic acid (9:1, v/v) to remove template in SPE cartridges,
115
and then further purified with deionized water and methanol successively by Soxhlet
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extraction before drying at 60 °C under vacuum for 48 h. The obtained GUF-MIR was
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used as sorbent for further PT-SPE work. Glyoxal-urea–formaldehyde non-imprinted
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resin (GUF-NIR) was prepared in a similar procedure except not being added
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template molecules in the preparing of MIRs.
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Procedures of GUF-MIR-PT-SPE. The spinach samples, purchased from local
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supermarkets of Baoding, were juiced and centrifuged by a super centrifuge at 8000
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rpm for 15 min, repeated 3 times. The supernatant was filtered and frozen in a
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refrigerator (−16 °C). The frozen sample thawed to two layers at room temperature
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and the upper solution was collected for the GUF-MIR-PT-SPE procedure.
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GUF-MIR (5.0 mg) was packed into a pipette tip sealed with two small pieces of
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cotton at both ends. After preconditioning with 1.0 mL of water, 1.0 mL of the spinach
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sample was loaded on the pipette tip cartridge, and then washed with 0.7 mL of
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MeOH‒H2O (1:1, v/v) and eluted with 0.6 mL of cyclohexane–ethyl acetate (9:1, v/v).
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The effluent was dried under nitrogen (0.1 MPa) at room temperature and then
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re-dissolved with 0.5 mL of hexane for GC analysis. The speed of the effluents in the
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whole GUF-MIR-PT-SPE process was controlled to approximately 0.05 mL/min by 6
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the blow-out with a rubber suction bulb.
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Rebinding Experiment. For the static adsorption experiment, 10.0 mg of GUF-MIR
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or GUF-NIR was mixed with 2.0 mL of the organochlorine pesticides aqueous
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solution in a centrifuge tube. The solutions were constituted with DCF, DDD, and
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tetradifon of which the concentrations ranged from 2.0 to 25.0 µg/mL. After shaking
137
for 12 h, the mixture was centrifuged, and the upper solution was analyzed by
138
HPLC‒UV to calculate the adsorption capacity of the materials.
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RESULTS AND DISCUSSION
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Synthesis of GUF-MIR. Many studies have explored the curing mechanism of UF
141
resin31 and the most recognized curing mechanism is shown in Figure 1. Using urea
142
and formaldehyde as functional monomers and 4, 4'-dichlorobenzhydrol as dummy
143
template, GUF-MIR was synthesized by precipitation polymerization. Hydroxymethyl
144
urea formed by the reaction of urea and formaldehyde could interact with the template
145
mainly by hydrogen bond (step 2, Figure 1). After the polycondensation process and
146
template elution procedure, the imprinted pores maintained in the three-dimensional
147
network of GUF-MIR. Because of the introduction of glyoxal and formaldehyde,
148
abundant hydroxyls formed after the reaction, and carbonyls formed on the material
149
with the addition of urea. Also, ether linkages appeared after the polycondensation
150
process. The formation of hydroxyls, carbonyls, and ether linkages increases the
151
hydrophilic ability of GUF-MIR, which makes the materials suitable to be applied as
152
adsorbent in aqueous solution.
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Morphology of GUF-MIR. At first, GUF-MIR was prepared at different 7
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glyoxal/formaldehyde (G/F) molar ratio of 0:1, 1:3, 1:2, and 1:1. The morphology of
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obtained materials was confirmed by SEM images (Figure 2). When increasing the
156
ratio of G/F, the particle size became smaller and the surface morphology of
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microspheres also changed. The maximum roughness would be reached when the
158
ratio of G/F increased to 1:2, while cracks appeared on the particle surface when the
159
ratio reached 1:1. It was because too much glyoxal attached on the surface of
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GUF-MIR blocking the reaction of urea and formaldehyde. The heterogeneous
161
distribution and different amounts of glyoxal would change the morphology of
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microspheres. Rougher particle surface could increase the specific surface area of
163
particles and improve the adsorption ability of GUF-MIR. In consideration of the
164
adsorption quantity for target analytes and the integrity of particles, G/F molar ratio of
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1:2 was employed for further work.
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Because 4,4'-dichlorobenzhydrol is insoluble in water, Tween 80 was employed to
167
increase its solubility. The amount of Tween 80 (0, 0.5, 1.0, 1.5, 2.0, and 4.0 mL) was
168
investigated to observe the effect of Tween 80 on the material surface without adding
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4,4'-dichlorobenzhydrol. According to Figure 3, the particle size turned small with the
170
existence of Tween 80, but the particle size only changed a little when the amount of
171
Tween 80 ranged from 1.0 to 2.0 mL. Besides, Tween 80 could make the material
172
surface rough and adhesive. A rough surface would increase the material’s specific
173
surface area, but a high adhesive degree would not be beneficial. The materials with
174
1.0, 1.5, and 2.0 mL of Tween 80 had appropriate particle size, rough surface, and low
175
adhesive degree. Considering the full dissolution of 4,4'-dichlorobenzhydrol in water, 8
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2.0 mL of Tween 80 was used for further work.
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Infrared Spectra of GUF-MIR and GUF-NIR. The FT-IR spectra of GUF-MIR
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and GUF-NIR were obtained by an FT-IR spectrometer (VERTEX70) (Figure S1 in
179
Supporting Information). For the two FT-IR chromatograms, the C=O peak was
180
observed at 1695 cm-1 and the strong and wide absorption band near 3360 cm-1 was
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attributed to the superposition of the stretching vibration of O-H and the stretching
182
vibration of N-H. It was worth noting that the appearance of the absorption band at
183
1243 cm-1 indicated the existence of C-O-C. Besides, there were absorption bands at
184
1040 and 1243 cm-1, which could be ascribed, respectively, to the C-O and C-N
185
stretching vibrations. The similar FT-IR spectra of GUF-MIR and GUF-NIR indicated
186
that the template molecules had been completely washed out.
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Adsorption Capacity of GUF-MIR. A static adsorption experiment was employed
188
to investigate the adsorption capacity of GUF-MIR and GUF-NIR at room
189
temperature. The results in Figure S2 showed that the adsorption amounts of the three
190
organochlorine pesticides (DCF, DDD, and tetradifon) on GUF-MIR and GUF-NIR
191
both increased with an increasing concentration, and the adsorption amounts gradually
192
tended to be saturated when the concentrations of the organochlorine pesticides were
193
more than 15 µg/mL. The adsorption amounts of DCF, DDD, and tetradifon on
194
GUF-MIR could reach 230, 360, and 255 µg/g, respectively while the adsorption
195
amounts on GUF-NIR were 180, 291, and 210 µg/g, respectively. These all indicated
196
that GUF-MIR had higher affinity to the three analytes than GUF-NIR and the effect
197
of imprinting played an important role in extracting the target compounds. In order to 9
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evaluate the imprinting effect of GUF-MIR, one competitive adsorption experiment
199
was performed in this work. Atrazine and ITA, whose structures are very different
200
from the added dummy template, were kept as controls. The result in Figure S3
201
showed that the adsorption amounts of the three kinds of organochlorine pesticides
202
were higher than those of atrazine and ITA. GUF-MIR had a good adsorption
203
performance for the analyes that had similar structures to 4, 4'-dichlorobenzhydrol.
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To further investigate the reproducibility of the preparation procedure of GUF-MIR,
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four batches of GUF-MIR were synthesized and evaluated with the above adsorption
206
experiment. The results demonstrated that the adsorption capacity of GUF-MIR
207
remained unaltered between the four batches with relative standard deviations (RSDs)
208
≤5.9% (n=4), which reveals the preparation of GUF-MIR is robust and reproducible.
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Optimization of GUF-MIR-PT-SPE Method. To achieve satisfactory recoveries
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of trace levels of DCF, DDD, and tetradifon in spinach samples, several parameters of
211
GUF-MIR-PT-SPE procedures were investigated including the kind and volume of
212
washing solvent and elution solvent. The washing step played a crucial role in
213
maximizing the specific interaction between the analytes and imprinted pores and
214
removing impurities originating from sample matrices. Different kinds of washing
215
solvents such as MeOH–H2O (1:1, v/v), ACN–H2O (1:1, v/v), MeOH, ACN, and
216
n-hexane–acetone (19:1, v/v) were investigated (1.0 mLof spiked spinach sample (88
217
ng/g), 0.8 mL of each washing solvent), and the results in Figure 4 showed that
218
MeOH–H2O (1:1, v/v) provided better recoveries than other washing solvents and
219
gave a satisfactory purification effect, so it was employed as the washing solvent. To 10
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determine the appropriate washing solvent volume, various volumes (0.3, 0.5, 0.7, 1.0,
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1.2, and 1.5 mL) of MeOH–H2O (1:1, v/v) were investigated. The results (Figure 4)
222
indicated that satisfactory recoveries were obtained if the volume of washing solvent
223
was less than 0.7 mL, whereas recoveries gradually decreased if the volume of
224
washing solvent was more than 0.7 mL. Considering recovery and purification effect,
225
0.7 mL of MeOH–H2O (1:1, v/v) was selected as the optimal washing solvent.
226
A suitable elution solvent should ensure that the analytes can be adequately eluted
227
from the adsorbent. Various kinds of elution solvents such as acetone–HOAc (9:1,
228
v/v), n-hexane–acetone (8:2, v/v), ethyl acetate, dichloromethane–HOAc (85:15, v/v),
229
and cyclohexane–ethyl acetate (9:1, v/v) were investigated in this study (1.0 mL of
230
each elution solvent was used). As shown in Figure 5, cyclohexane–ethyl acetate (9:1,
231
v/v) had the highest elution efficiency and was selected as the elution solvent for
232
further work. Different volumes of cyclohexane–ethyl acetate (9:1, v/v) (0.2, 0.4, 0.6,
233
0.8, 1.0, 1.2, and 1.4 mL) were investigated. After optimization, 0.6 mL of
234
cyclohexane–ethyl acetate (9:1, v/v) was selected as the elution solvent.
235
Comparison
with
Different
Adsorbents.
To
further
demonstrate
the
236
characteristics of GUF-MIR, various adsorbents such as GUF-MIR, GUF, C18, silica
237
gel, NH2-silica gel, and Al2O3-N of PT-SPE were investigated. The extraction
238
conditions (preconditioning, loading, washing, and elution) of C18, silica gel,
239
NH2-silica gel, and Al2O3-N were optimized based on previous publications32‒35 and
240
the result (Figure 6) showed that the recoveries of the three organochlorine pesticides
241
on the four adsorbents were 35.8%‒45.6%, 39.6%‒54.4%, 39.0%‒54.7%, and 11
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30.2%‒61.5%, respectively. The extraction conditions of GUF (recoveries were
243
75.2%‒83.3%) were the same as those of GUF-MIR due to the fact that the two
244
materials were prepared in an identical procedure except the addition of template.
245
GUF-MIR received the highest recoveries (91%‒97%) with better purification
246
efficiency. The above results implied higher affinity and selectivity of GUF-MIR than
247
other adsorbents.
248
The reagents in the preparation of GUF-MIR, such as glyoxal, urea, formaldehyde,
249
and Tween 80 are all inexpensive and cheaper than the common reagents of traditional
250
MIPs (methacrylic acid, acrylamide, ethylene glycol dimethacrylate, etc). Besides, the
251
preparation conditions are easy, so the cost of large-scale production of GUF-MIR is
252
relatively low. Moreover, from the comparison with commercial adsorbents such as
253
C18, silica gel, NH2-silica gel, and Al2O3-N for extraction of the three OCPs in spinach,
254
GUF-MIR not only obtained the highest recoveries, but also had the best purification
255
effect. All of these reasons make the commercial distribution of GUF-MIR possible.
256
Validation of GUF-MIR-PT-SPE-GC Method. Under the optimized conditions,
257
experiments were performed to determine linearity, limit of detection (LOD), limit of
258
quantification (LOQ), accuracy, and precision of the GUF-MIR-PT-SPE method.
259
Blank spinach samples were spiked with the three organochlorine pesticides to obtain
260
the spiked samples with seven concentrations in a range of 2.2‒220.0 ng/g. Then these
261
spiked samples were pretreated by the GUF-MIR-PT-SPE method and determined by
262
GC‒ECD method. Calibration curves of the three organochlorine pesticides were
263
obtained by plotting average peak area versus analyte concentration at the seven 12
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spiked concentrations and each spiked concentration was performed in triplicate.
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Good linearity was obtained for all organochlorine pesticides throughout the
266
concentration range, and the regression equations were listed in Table 1. The LOD
267
(signal-to-noise (S/N)=3) and LOQ (S/N=10) which were methodological evaluation
268
were ranged from 0.24 ng/g to 0.66 ng/g and 1.90 ng/g to 2.20 ng/g, respectively.. The
269
accuracy
270
GUF-MIR-PT-SPE with spiked spinach samples (88 ng/g) on the same day (n=3) and
271
on consecutive three days. The intra-day and inter-day precision expressed as relative
272
standard deviations (RSDs) were 3.5% to 4.9% and 5.8% to 6.7%, respectively. The
273
recoveries of the three organochlorine pesticides at three spiked levels (2.2, 22.0, and
274
220.0 ng/g) by performing three replicates ranged from 89.1% to 101.9% with RSDs
275
≤7.1% (Table 2). The present method is compared with previous reported methods
276
and the result in Table S1 in Supporting Information shows that the recovery of
277
GUF-MIR-PT-SPE-GC method is higher than or similar to other methods and the
278
LOD is low enough for trace analysis of the three analytes.
and
precision
of
the
method
were
evaluated
by
performing
279
Assay of Organochlorine Pesticides in Spinach Samples. To assess the
280
performance of the proposed GUF-MIR-PT-SPE-GC method, the five kinds of
281
spinach samples collected from the local markets in Baoding (Hebei, China) were
282
processed and determined under the optimal conditions. The chromatograms showed
283
that only DCF was determined in one of the five spinach samples at the level of 18.9
284
ng/g, which was lower than the national residue limit of 0.1 mg/kg in China (Figure
285
7A). None of the three analytes was detected in the other four spinach samples. 13
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Moreover, the chromatograms obtained from spinach samples are much cleaner after
287
the GUF-MIR-PT-SPE process, and blank and spiked spinach samples revealed that
288
no interfering peaks originating from spinach matrices
289
retention time of the analytes after GUF-MIR-PT-SPE, which indicates that the
290
proposed method exhibits significantly purification effect and good application
291
potential (Figure 7B).
292
AUTHOR INFORMATION
293
Corresponding Author
294
∗
295
Funding Sources
were observed at the
Tel.: +86-312-5079788. Fax: +86-312-5971107. E-mail:
[email protected].
296
The project is sponsored by the National Natural Science Foundation of China
297
(21575033), the Natural Science Foundation of Hebei Province (B2015201132), and
298
Natural Science Foundation of Education Department of Hebei Province (ZD2015036)
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REFERENCES
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(1) Zhang, A.; Fang, L.; Wang, J.; Liu, W.; Yuan, H.; Jantunen, L.; Li, Y. Residues of
301
currently and never used organochlorine pesticides in agricultural soils from Zhejiang
302
Province, China. J. Agric. Food Chem. 2012, 60, 2982‒2988.
303
(2) Zhang, A.; Luo, W.; Sun, J.; Xiao, H.; Liu, W. Distribution and uptake pathways of
304
organochlorine pesticides in greenhouse and conventional vegetables. Sci. Total
305
Environ. 2015, 505, 1142‒1147.
306
(3) Fujii, Y.; Haraguchi, K.; Harada, K.; Hitomi, T.; Inoue, Kayoko.; Itoh, Y.;
307
Watanabe, T.; Takenaka, K.; Uehara, S.; Yang, H.; Kim, M.; Moon, C.; Kim H.; Wang,
308
P.; Liu, A.; Hung, N.; Koizumi, A. Detection of dicofol and related pesticides in
309
human breast milk from China, Korea and Japan. Chemosphere 2011, 82, 25‒31.
310
(4) Qi, D.; Fei, Ting.; Sha, Yunfei.; Wang, Leijun.; Li, G.; Wu, Da.; Liu, B. A novel
311
fully automated on-line coupled liquid chromatography–gas chromatography
312
technique used for the determination of organochlorine pesticide residues in
313
tobacco and tobacco products. J. Chromatogr. A 2014, 1374, 273‒277.
314
(5) Mastovska, K.; Dorweiler, K. J.; Lehotay, S. J.; Wegscheid, J. S.; Szpylka, K. A.
315
Pesticide multiresidue analysis in cereal grains using modified QuEChERS method
316
combined with automated direct sample introduction GC-TOFMS and UPLC-MS/MS
317
techniques. J. Agric. Food Chem. 2010, 58, 5959‒5972.
318
(6) Chen, L,; Ding, L.; Jin, H.; Song, D.; Zhang, H.; Li, J.; Zhang, K.; Wang, Y.;
319
Zhang, H. The determination of organochlorine pesticides based on dynamic
320
microwave-assisted extraction coupled with on-line solid-phase extraction of 15
ACS Paragon Plus Environment
Journal of Agricultural and Food Chemistry
Page 16 of 31
321
high-performance liquid chromatography. Anal. Chim. Acta 2007, 589, 239‒246.
322
(7) Santhi, V. A.; Hairin, T.; Mustafa, A. M. Simultaneous determination of
323
organochlorine pesticides and bisphenol A in edible marine biota by GC–MS.
324
Chemosphere 2012, 86, 1066‒1071.
325
(8) Patil, S. H.; Banerjee, K.; Dasgupta, S.; Oulkar, D. P.; Patil, S. B.; Jadhav, M. R.;
326
Savant R. H.; Adsule, P. G.; Deshmukh, M. B. Multiresidue analysis of 83 pesticides
327
and
328
chromatography–time-of-flight mass spectrometry. J. Chromatogr. A 2009, 1216,
329
2307‒2319.
330
(9) Dias, A. N.; Simão, V.; Merib, J.; Carasek, E. Use of green coating (cork) in
331
solid-phase microextraction for the determination of organochlorine pesticides in
332
water by gas chromatography-electron capture detection. Talanta 2015, 134, 409‒414.
333
(10) Fernandes, V. C.; Domingues, V. F.; Mateus, N.; Delerue-Matos, C.
334
Organochlorine pesticide residues in strawberries from integrated pest management
335
and organic farming. J. Agric. Food Chem. 2011, 59, 7582‒7591.
336
(11) Zhang, M.; Huang, J.; Wei, C.; Yu, B.; Yang, X.; Chen, X. Mixed liquids for
337
single-drop microextraction of organochlorine pesticides in vegetables. Talanta 2008,
338
74, 599‒604.
339
(12) Rissato, S. R.; Galhiane, M. S.; Knoll, F. R.; Apon, B. M. Supercritical fluid
340
extraction for pesticide multiresidue analysis in honey: determination by gas
341
chromatography with electron-capture and mass spectrometry detection. J.
342
Chromatogr. A 2004, 1048, 153‒159.
12
dioxin-like
polychlorinated
biphenyls
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in
wine
by
gas
Page 17 of 31
Journal of Agricultural and Food Chemistry
343
(13) Łozowicka, B.; Jankowska, M.; Kaczyński, P. Pesticide residues in Brassica
344
vegetables and exposure assessment of consumers. Food Control 2012, 25, 561‒575.
345
(14) Li, Z.; Chen, P.; Yu, C.; Fang, Y.; Wang, Z.; Li, M.; Shan, H. A novel
346
temperature-controlled ionic liquid dispersive liquid phase microextraction for
347
determination of dicofol and DDT in environmental water samples prior to gas
348
chromatography mass spectrometry. Curr. Anal. Chem. 2009, 5, 324‒329.
349
(15) Coscollà, C.; Castillo, M.; Pastor, A.; Yusà, V. Determination of 40 currently used
350
pesticides in airborne particulate matter (PM 10) by microwave-assisted extraction
351
and gas chromatography coupled to triple quadrupole mass spectrometry. Anal. Chim.
352
Acta 2011, 693, 72‒81.
353
(16) Ji, J.; Deng, C.; Zhang, H.; Wu, Y.; Zhang, X. Microwave-assisted steam
354
distillation for the determination of organochlorine pesticides and pyrethroids in
355
Chinese teas. Talanta 2007, 71, 1068–1074.
356
(17) Giordano, A.; Fernández-Franzón, M.; Ruiz, M. J.; Font, G.; Picó, Y. Pesticide
357
residue determination in surface waters by stir bar sorptive extraction and liquid
358
chromatography/tandem mass spectrometry. Anal. Bioanal. Chem. 2009, 393,
359
1733‒1743.
360
(18) Berendsen, B. J. A.; Nielen, M. W. F. Selectivity in the sample preparation for the
361
analysis of drug residues in products of animal origin using LC‒MS. Trends Anal.
362
Chem. 2013, 43, 229‒239.
363
(19) Shen, Q.; Dong, W.; Wang, Y.; Gong, L.; Dai, Z.; Cheung, H. Pipette tip
364
solid-phase
extraction
and
ultra-performance
liquid
17
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chromatography/mass
Journal of Agricultural and Food Chemistry
Page 18 of 31
365
spectrometry based rapid analysis of picrosides from Picrorhiza scrophulariiflora. J.
366
Pharm. Biomed. Anal. 2013, 80, 136‒140.
367
(20) Yan, H.; Yang, C.; Sun, Y.; Row, K. H. Ionic liquid molecularly imprinted
368
polymers for application in pipette-tip solid-phase extraction coupled with gas
369
chromatography for rapid screening of dicofol in celery. J. Chromatogr. A 2014, 1361,
370
53‒59.
371
(21) Kumazawa, T.; Hasegawa, C.; Lee, X.; Hara, K.; Seno, H.; Suzuki, O.; Sato, K.
372
Simultaneous determination of methamphetamine and amphetamine in human urine
373
using pipette tip solid-phase extraction and gas chromatography–mass spectrometry. J.
374
Pharm. Biomed. Anal. 2007, 44, 602‒607.
375
(22) Zhu, G.; He, X.; Li, X.; Wang, S.; Luo, Y.; Yuan, B.; Feng, Y. Preparation of
376
mesoporous silica embedded pipette tips for rapid enrichment of endogenous peptides.
377
J. Chromatogr. A 2013, 1316, 23‒28.
378
(23) Augusto, F.; Hantao, L. W.; Mogollón, N. G.; Braga, S. C. New materials and
379
trends in sorbents for solid-phase extraction. Trends Anal. Chem. 2013, 43, 14‒23.
380
(24) Martín-Esteban, A. Molecularly-imprinted polymers as a versatile, highly
381
selective tool in sample preparation. Trends Anal. Chem. 2013, 45 169‒181.
382
(25) Yan, H.; Sun, N.; Han, Y.; Yang, C.; Wang, M.; Wu, R. Ionic liquid-mediated
383
molecularly
384
chromatography-electron capture detector for rapid screening of dicofol in vegetables.
385
J. Chromatogr. A 2013, 1307, 21‒26.
386
(26) Pichon, V. Selective sample treatment using molecularly imprinted polymers. J.
imprinted
solid-phase
extraction
18
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coupled
with
gas
Page 19 of 31
Journal of Agricultural and Food Chemistry
387
Chromatogr. A 2007, 1152, 41‒53.
388
(27) Fan, J.; Tian, Z.; Tong, S.; Zhang, X.; Xie, Y.; Xu, R.; Qin, Y.; Li, L.; Zhu, J.;
389
Ouyang, X. A novel molecularly imprinted polymer of the specific ionic liquid
390
monomer for selective separation of synephrine from methanol–water media. Food
391
Chem. 2013, 141, 3578‒3585.
392
(28) Deng, S.; Pizzi, A.; Du, G.; Zhang, J.; Zhang, J. Synthesis, Structure, and
393
Characterization of Glyoxal-Urea-Formaldehyde Cocondensed Resins. J. Appl. Polym.
394
Sci. 2014, doi: 10.1002/APP.41009.
395
(29) Liu, Z.; Du, Z.; Song, H.; Wang, C.; Subhan, F.; Xing, W.; Yan, Z. The
396
fabrication of porous N-doped carbon from widely available urea formaldehyde resin
397
for carbon dioxide adsorption. J. Colloid Interface Sci. 2014, 416, 124–132.
398
(30) Philbrook, A.; Blake, C. J.; Dunlop, N.; Easton, C. J.; Keniry, M. A.; Simpson, J.
399
S. Demonstration of co-polymerization in melamine–urea–formaldehyde reactions
400
using 15N NMR correlation spectroscopy. Polymer 2005, 46, 2153–2156.
401
(31) Guo, Z.; Guo, T.; Guo, M. Preparation of molecularly imprinted adsorptive resin
402
for trapping of ligustrazine from the traditional Chinese herb Ligusticum chuanxiong
403
Hort. Anal. Chim. Acta 2008, 612, 136‒143.
404
(32) Netto, P. T.; Júnior, O. J. T.; de Camargo, J. L. V.; Ribeiro, M. L.; de Marchi, M.
405
R. R. A rapid, environmentally friendly, and reliable method for pesticide analysis in
406
high-fat samples. Talanta 2012, 101, 322‒329.
407
(33) Chen, S.; Yu, X.; He, X.; Xie, D.; Fan, Y.; Peng, J. Simplified pesticide
408
multiresidues analysis in fish by low-temperature cleanup and solid-phase extraction 19
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Journal of Agricultural and Food Chemistry
409
coupled with gas chromatography/mass spectrometry. Food Chem. 2009, 113,
410
1297‒1300.
411
(34) Osman, K. A.; Ibrahim, G. H.; Askar, A. I.; Alkhail, A. R. A. A. Biodegradation
412
kinetics of dicofol by selected microorganisms. Pestic. Biochem. Physiol. 2008, 91,
413
180‒185.
414
(35) Dey, S.; Bakthavatchalu, V.; Tseng, M. T.; Wu, P.; Florence, R. L.; Grulke, E. A.;
415
Yokel, R. A.; Dhar, S. K.; Yang, H.; Chen, Y.; St Clair, D. K. Interactions between
416
SIRT1 and AP-1 reveal a mechanistic insight into the growth promoting properties of
417
alumina (Al2O3) nanoparticles in mouse skin epithelial cells. Carcinogenesis 2008, 29,
418
1920–1929.
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List of Tables and Figures Table 1. Features of GUF-MIR-PT-SPE method. Table 2. Recoveries of GUF-MIR-PT-SPE method for spiked spinach samples. Figure 1. Schematic illustration of GUF-MIR’s formation. Figure 2. SEM images of four kinds of materials with different ratios of glyoxal and formaldehyde (A. 0:1, B. 1:3, C. 1:2, D. 1:1). Figure 3. SEM images of six kinds of materials with different amounts of Tween 80 (A. 0, B. 0.5 mL, C. 1.0 mL, D. 1.5 mL, E. 2.0 mL, F. 4.0 mL). Figure 4. Effect of different washing solvents and volume of MeOH–H2O (1:1, v/v). 1. n-hexane–acetone (19:1, v/v), 2. ACN, 3. MeOH, 4. ACN–H2O (1:1, v/v), 5. MeOH–H2O (1:1, v/v). Figure 5. Effect of different elution solvents and volume of cyclohexane‒ethyl acetate (9:1, v/v). 1. cyclohexane‒ethyl acetate (9:1, v/v), 2. dichloromethan–HOAc (85:15, v/v), 3. ethyl acetate, 4. n-hexane–acetone (8:2, v/v), 5. acetone–HOAc (9:1, v/v). Figure 6. Purification effect and recoveries of different adsorbents. Figure 7. Chromatograms of spinach sample containing DCF (A), blank spinach sample (B, a), and spiked spinach sample (B, b) after GUF-MIR-PT-SPE.
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Table 1. Features of GUF-MIR-PT-SPE method. RSD (%) Analytes
Regression equation
2
r
Linearity (ng/g)
LOD (ng/g)
LOQ (ng/g) intra-day
inter-day
DCF
Y = 4.937 × 103x + 9.001 ×103
0.9996
2.2‒220.0
0.66
2.20
3.6
6.7
DDD
Y = 1.795 × 104x + 2.022 ×104
0.9999
2.2‒220.0
0.24
0.78
4.9
5.8
Tetradifon
Y = 1.597 × 104x + 3.383 ×104
0.9997
2.2‒220.0
0.58
1.90
3.5
6.7
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Table 2. Recoveries of GUF-MIR-PT-SPE method for spiked spinach samples. Analytes
2.2 (ng/g)
22.0 (ng/g)
220.0 (ng/g)
Recoveries (%)
RSD (%)
Recoveries (%)
RSD (%)
Recoveries (%)
RSD (%)
Dicofol
92.4
6.1
96.2
7.1
97.8
4.0
DDD
89.1
3.2
94.6
5.5
95.4
6.4
Tetradifon
92.6
4.1
99.2
1.3
101.9
3.5
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Step 1 Aldol condensation H N
HO
H H NH2 C C O O Functional monomer A Formaldehyde HO
H
H H2 N NH2 C C O O Urea Formaldehyde
C H2
C H2
H N
H N
C
C H2
OH
O Functional monomer B
Step 2 Prearrangement
C H2
H N
Functional monomer A/B
Cl
H N CH H H
CH N H H H Cl
Cl
H
Cl
H
H
N CH OH
H
H
H
OH
N
H
CH
H N CH
H
Template molecule Template-monomer complex Step 3 Monomer polymerization and the formation of GUF-MIR
x
HO
C H2
H N
C
HO
NH2 y
O Functional monomer A H+
C H2
H N
H N
O OH
C C H2 O Functional monomer B
z H
C
H C
O Glyoxal
Copolymerization
Cl
H N CH H
CH N H H
H N CH H H
CH N H H H
Washing temple
Cl
Rebinding H
H
H
N CH
H H
H
N
OH CH
H
H
H
N
N
N
CH
CH
H
H
H
H
CH N
CH
H
Figure 1. Schematic illustration of GUF-MIR’s formation.
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Figure 2. SEM images of four kinds of materials with different ratios of glyoxal and formaldehyde (A. 0:1, B. 1:3, C. 1:2, D. 1:1).
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Figure 3. SEM images of six kinds of materials with different amounts of Tween 80 (A. 0, B. 0.5 mL, C. 1.0 mL, D. 1.5 mL, E. 2.0 mL, F. 4.0 mL).
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X2 (Volume of MeO
0.3 0.5 0.7
H-H O (1:1, v/v), 2 mL) 1.0 1.2 1.5
100 96 92 88 84 80
y , %) Y 1 (Recovr
100 80 60 40 20 0
%)
Tetradifon DDD DCF
Y2 (Recovry,
Page 27 of 31
DCF 5
DDD 4
3 X (K 1 2 ind o f was 1 hing solve nt)
Tetradifon
Figure 4. Effect of different washing solvents and volume of MeOH–H2O (1:1, v/v). 1. n-hexane–acetone (19:1, v/v), 2. ACN, 3. MeOH, 4. ACN–H2O (1:1, v/v), 5. MeOH–H2O (1:1, v/v).
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X (Volu 2 m
e of cyc
lohexan e-ethyl
1.4 1.2 1.0 0.8
0.6
acetate
0.4 0.2
(9:1, v/v
40
Y1 (Recovry, %)
20 0 100 80 60 40 20 0
Y2 (Recovry, %
100 80 60
), m L )
)
Tetradifon DDD DCF
Page 28 of 31
DCF 1
DDD
2 3 X ( 1 Ki n d of elut ion
Tetradifon
4
solv ent)
5
Figure 5. Effect of different elution solvents and volume of cyclohexane‒ethyl acetate (9:1, v/v). 1. cyclohexane‒ethyl acetate (9:1, v/v), 2. dichloromethan–HOAc (85:15, v/v), 3. ethyl acetate, 4. n-hexane–acetone (8:2, v/v), 5. acetone–HOAc (9:1, v/v).
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DCF GUF-MIR GUF-NIR Al O -N 2 3
DDD
Tetradifon 100 80
NH2-silica gel silica gel C18
60 40 20 0
560 DCF
490
DDD
Tetradifon Al2O3-N
Voltage ( mV)
420
C18
350 290
NH2
210
Si
140
GUF-NIR
70
GUF-MIR 0
2
4
6
8
10
12
14
Time (min)
Figure 6. Purification effect and recoveries of different adsorbents.
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A
Voltage (mV)
80 60 40
DCF
20 0 -20 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
500
Voltage (mV)
B
a: Blank sample b: Spiked sample
400 300
Tetradifon
DDD
DCF 200
b
100
a
0 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Time (min)
Figure 7. Chromatograms of spinach sample containing DCF (A), blank spinach sample (B, a), and spiked spinach sample (B, b) after GUF-MIR-PT-SPE.
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Graphical Abstract: Step 1 Aldol condensation H N
HO
H H NH2 C C O O Functional monomer A Formaldehyde HO
H
H H2N NH2 C C O O Urea Formaldehyde
C H2
C H2
H N
H N
C
C H2
OH
O Functional monomer B
Step 2 Prearrangement
C H2
H N
Functional monomer A/B
Cl
H N CH H H
CH N H H H Cl
Cl
H
Cl
H
H
N CH OH
H H
H
N
OH CH
H N CH
H
H
Template molecule Template-monomer complex Step 3 Monomer polymerization and the formation of GUF-MIR
x
HO
C H2
H N
C
HO
NH2 y
O Functional monomer A H+
C H2
H N
H N
O OH
C C H2 O Functional monomer B
z H
C
O Glyoxal
Copolymerization
Cl
H N CH H
CH N H H
H N CH H H
CH N H H H
Washing temple
Cl
Rebinding H
H
H
N CH
H
H
H
OH
N
H
CH
H C
H
H
H
N
N
N
CH
CH
CH
H
H
H
N
CH
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H
H