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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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Journal of Agricultural and Food Chemistry

1

Glyoxal-Urea-Formaldehyde Molecularly Imprinted Resin as

2

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

ACS Paragon Plus Environment


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capacity for DCF, DDD, and tetradifon in aqueous solution. The average recoveries at

23

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

29

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

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bioaccumulation that are very harmful to wild animals and human beings.2‒4 Thus a

40

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


mass

have been spectrometry

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(LC–MS/MS),5

45

(HPLC‒UV),6 and gas chromatography–tandem mass spectrometry (GC–MS/MS).7,8

46

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

49

(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

53

extraction

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microwave-assisted steam distillation (MASD),16 and stir-bar sorptive extraction

55

(SBSE)17 are often employed for the extraction and purification of OCPs. Besides,

56

generic extraction methods (such as QuEChERS, SPE, etc) are developed to extract

57

target compounds simultaneously, but one obvious drawback is the occurrence of

58

abundant interference components originating from sample matrices due to the low

59

selectivity of the adsorbents, which compromise detection limits, quantitative aspects,

60

and method selectivity.18 Among these methods, SPE is the most widely used for

61

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,

64

ease of operation, time efficiency, and versatility.21,22 However, the common

65

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


detector

(MAE‒GPC),15


66

owing to the lack of specific recognition to analytes in complex samples. Thus,

67

adsorbents with selective affinity are desired greatly.

68

In the last decade, the use of molecularly imprinted polymers (MIPs) in SPE have

69

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

71

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

73

monomer can be introduced in the synthetic procedure of MIR, which can improve

74

the compatibility with polar solutions and reduce the toxic reagent compared with UF

75

gel.28‒31

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In this study, a new type of glyoxal-urea-formaldehyde molecularly imprinted resin

77

(GUF-MIR) was fabricated with GUF gel as functional monomer and 4,

78

4'-dichlorobenzhydrol as dummy template. GUF-MIR was employed as PT-SPE

79

adsorbent for the rapid isolation of OCPs (DCF, DDD, and tetradifon) in five kinds of

80

spinach. The proposed sample pretreatment method combining the advantages of

81

MIPs, GUF, and PT-SPE could be used in aqueous matrices with high affinity and

82

selectivity to the analytes in complex samples.

83

EXPERIMENTAL PROCEDURES

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Chemicals and Reagents. DCF was purchased from Dacheng Pesticide Co., Ltd.

85

(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).

89

3-indolebutyric acid (ITA) and atrazine were obtained from Aladdin Reagent Co., Ltd.

90

(Shanghai, China). Methanol (MeOH, HPLC grade), acetonitrile (ACN, HPLC grade),

91

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)

93

was obtained from Tianjin Guangfu Technology Development Co., Ltd. (Tianjin,

94

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

96

filtered with a 0.45-µm filter membrane before use.

97

Instrumentation and Conditions. GC analysis was performed on a GC-2014 gas

98

chromatography (Shimadzu, Japan) equipped with a split/splitless injector and an

99

electron capture detector (ECD). A WM-5 capillary column (5% diphenyl‒

100

dimethylpolysiloxane, 30 m × 0.25 mm × 0.25 µm) was obtained from Welch

101

Materials Co., Ltd. (Shanghai, China). An N-2000 data workstation (Zheda Zhineng

102

Co., Ltd., Hangzhou, China) was used as the data acquisition system. High purity

103

nitrogen (99.999%) was employed as the carrier gas of GC. The injection port, oven

104

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

106

(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.

109

Synthesis of GUF-MIR. 4,4'-dichlorobenzhydrol (0.2776 g) was dissolved fully 5



110

into Tween 80 (2.0 mL) by ultrasonic and stirring in a beaker, after which distilled

111

water (80.0 mL), urea (4.5 g), formaldehyde (12.0 mL), and glyoxal (9.2 mL) were

112

added successively with stirring. After standing for 1 h, acetic acid (0.4 mL) was

113

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

116

extraction before drying at 60 °C under vacuum for 48 h. The obtained GUF-MIR was

117

used as sorbent for further PT-SPE work. Glyoxal-urea–formaldehyde non-imprinted

118

resin (GUF-NIR) was prepared in a similar procedure except not being added

119

template molecules in the preparing of MIRs.

120

Procedures of GUF-MIR-PT-SPE. The spinach samples, purchased from local

121

supermarkets of Baoding, were juiced and centrifuged by a super centrifuge at 8000

122

rpm for 15 min, repeated 3 times. The supernatant was filtered and frozen in a

123

refrigerator (−16 °C). The frozen sample thawed to two layers at room temperature

124

and the upper solution was collected for the GUF-MIR-PT-SPE procedure.

125

GUF-MIR (5.0 mg) was packed into a pipette tip sealed with two small pieces of

126

cotton at both ends. After preconditioning with 1.0 mL of water, 1.0 mL of the spinach

127

sample was loaded on the pipette tip cartridge, and then washed with 0.7 mL of

128

MeOH‒H2O (1:1, v/v) and eluted with 0.6 mL of cyclohexane–ethyl acetate (9:1, v/v).

129

The effluent was dried under nitrogen (0.1 MPa) at room temperature and then

130

re-dissolved with 0.5 mL of hexane for GC analysis. The speed of the effluents in the

131

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

134

or GUF-NIR was mixed with 2.0 mL of the organochlorine pesticides aqueous

135

solution in a centrifuge tube. The solutions were constituted with DCF, DDD, and

136

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.

139

RESULTS AND DISCUSSION

140

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.

153

Morphology of GUF-MIR. At first, GUF-MIR was prepared at different 7



154

glyoxal/formaldehyde (G/F) molar ratio of 0:1, 1:3, 1:2, and 1:1. The morphology of

155

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

157

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

160

GUF-MIR blocking the reaction of urea and formaldehyde. The heterogeneous

161

distribution and different amounts of glyoxal would change the morphology of

162

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

165

1:2 was employed for further work.

166

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

169

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.

177

Infrared Spectra of GUF-MIR and GUF-NIR. The FT-IR spectra of GUF-MIR

178

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

181

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.

187

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



198

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.

204

To further investigate the reproducibility of the preparation procedure of GUF-MIR,

205

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.

209

Optimization of GUF-MIR-PT-SPE Method. To achieve satisfactory recoveries

210

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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220

determine the appropriate washing solvent volume, various volumes (0.3, 0.5, 0.7, 1.0,

221

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



242

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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264

spiked concentrations and each spiked concentration was performed in triplicate.

265

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



286

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)

14


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REFERENCES

300

(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

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organochlorine pesticides in greenhouse and conventional vegetables. Sci. Total

305

Environ. 2015, 505, 1142‒1147.

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1920–1929.

20


Page 20 of 31

Page 21 of 31


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.

21



Page 22 of 31

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

22


Page 23 of 31


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

23



Page 24 of 31

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.

24


H

Page 25 of 31


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).

25



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).

26


Page 26 of 31


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).

27



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).

28


Page 29 of 31


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.

29



Page 30 of 31

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.

30


Page 31 of 31


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

31


H

H

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