Preparation of Magnetic Hollow Molecularly Imprinted Polymers for

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Preparation of Magnetic Hollow MIPs for Detection of Triazines in Food Samples Aixiang Wang, Hongzhi Lu, and Shoufang Xu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b01197 • Publication Date (Web): 03 Jun 2016 Downloaded from http://pubs.acs.org on June 9, 2016

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Journal of Agricultural and Food Chemistry

Graphical abstract

Magnetic hollow molecularly imprinted polymer (M-H-MIPs) were prepared based on multi-step swelling polymerization followed by post-imprinting in-situ growth magnetic Fe3O4 nanoparticles on the surface of hollow MIPs.

ACS Paragon Plus Environment


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Preparation of Magnetic Hollow MIPs for Detection of Triazines in Food

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Samples

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Aixiang Wang, Hongzhi Lu, Shoufang Xu*

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School of Chemistry and Chemical Engineering, Linyi University, Linyi 276005,

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China.

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*Corresponding author

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Tel.: +86 539 8766000; fax: +86 539 8766000.

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E-mail address: [email protected] (S.F. Xu)

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ABSTRACT

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Novel magnetic hollow molecularly imprinted polymers (M-H-MIPs) were proposed

25

for highly selective recognition and fast enrichment of triazines in food samples.

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M-H-MIPs were prepared based on multi-step swelling polymerization followed by

27

in-situ growth of magnetic Fe3O4 nanoparticles on the surface of hollow MIPs.

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Transmission electron microscopy and scanning electron microscope confirmed the

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successful immobilization of Fe3O4 nanoparticles on the surface of hollow MIPs.

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M-H-MIPs could be separated simply using an external magnet. The binding

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adsorption results indicated that M-H-MIPs displayed high binding capacity and fast

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mass transfer property and class selective property for triazines. Langmuir isotherm

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and pseudo-second-order kinetic models fitted the best adsorption models for

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M-H-MIPs. M-H-MIPs were used to analyze atrazine, simazine, propazine and

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terbuthylazine in corn, wheat and soybean samples. Satisfactory recoveries were in

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the range of 80.62%-101.69% and relative standard deviation was lower than 5.2%.

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Limits of detection from 0.16 to 0.39 µg·L-1 was obtained. When the method was

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applied to test positive samples that were contaminated with triazines, the results

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agree well with those obtained from accredited method. Thus, M-H-MIPs based

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DSPE method proved to be a convenient and practical platform for detection of

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triazines in food samples.

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KEYWORDS: molecularly imprinted polymers, magnetic hollow MIPs, in-situ

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growth, triazines, food sample



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INTRODUCTION

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Molecularly imprinted polymers (MIPs) are a kind of functional polymers which

47

display specific recognition performance to template molecules. Up to date, MIPs

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have been applied in many field, such as enrichment/separation1-3, electrochemical or

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optical chemical sensors4-6 and selective photocatalytic degradation7 because of their

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outstanding selectivity, physical and thermal stability. It should be pointed out that

51

although MIPs enjoy significant benefits and diverse applications, they still

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confronted with many problems resulted from the highly cross-linked nature of MIPs,

53

such as low binding capacity and slow mass transfer, which limiting its application in

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rapid detection of trace targets. Many strategies, including surface molecular

55

imprinting8,9, hollow porous MIPs10,11, mesoporous MIPs12-14 and solid phase

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synthesis method15,16 have been proposed to solve those problems. Among those novel

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MIPs, hollow MIPs (H-MIPs) have attracted increasingly attentions based on the fact

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that the holes on the surface and cavities in the core are benefit for mass transfer. The

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mild preparation conditions make seed swelling polymerization becoming the most

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commonly used method to prepare monodisperse H-MIPs.

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In the meanwhile, magnetic MIPs (M-MIPs) are also widely applied to extract

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targets in complicated matrix based on the fact that they can be isolated conveniently

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from sample solutions by an external magnet

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summarized many methods for preparing M-MIPs and the general process involves

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preparation and surface modification of magnetic nanoparticles, followed by coating

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MIPs. The common feature of those methods is that surface imprinting technique was

17

. In our previous work18, we have


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adopted using magnetic nanoparticles as cores.

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Magnetic hollow MIPs (M-H-MIPs) would possess the advantages of both hollow

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polymers and magnetic separation. However, M-H-MIPs have rarely been reported

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because the methods for preparing hollow polymers and magnetic polymers are often

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conflicted. So if magnetic nanoparticles are used as cores, it is hard to form H-MIPs.

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One feasible way is to immobilize magnetic nanoparticles on the surface of H-MIPs.

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Ye et al. presented an approach to immobilize Fe3O4 nanoparticles on the surface of

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MIPs by click reaction19. However, this method involves complicated surface

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modification process in order to introduce clickable azide groups or alkyne groups

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onto the surface of Fe3O4 nanoparticles or MIPs. Shi20 reported that Fe3O4 can be

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immobilized on the surface of MIPs by using glycidilmethacrylate (GMA) as

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co-monomers during the process of preparation MIPs. The role of GMA, which has

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an epoxide ring, is to offer potential hydroxyl groups for in situ growth of Fe3O4

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nanoparticles. Compared to click reaction, this method is easy to control.

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Inspired by the above mentioned studies, M-H-MIPs for detection of four triazines

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in food sample were prepared based on multi-step swelling polymerization followed

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by in-situ growth of magnetic Fe3O4 nanoparticles on the surface of H-MIPs. The

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as-prepared M-H-MIPs displayed many advantages in enrichment trace targets from

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complicated sample matrix, such as magnetic separation ability, molecule recognition

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ability and faster mass transfer ability. The structure of M-H-MIPs were characterized

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by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

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Binding capacity of M-H-MIPs, including static binding, dynamic binding and



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selective recognition ability were investigated detailed. The performances of

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M-H-MIPs for specific separation and enrichment of triazines in corn, soybean and

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wheat samples were studied. Under optimal conditions, the recoveries of the

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established methods were satisfactory. Moreover, M-H-MIPs were successfully

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applied to assess triazine herbicide residues in positive food samples. And the values

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agree with those obtained using the accredited classic method. This study provided an

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efficient, selective, and accurate method for analyzing triazine herbicide at trace

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abundance in multiple media.

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EXPERIMENTAL SECTION

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Materials and Chemicals. Divinylbenzene (DVB), methacrylic acid (MAA) and glycidilmethacrylate

(GMA)

were

from

Sigma-Aldrich

(Shanghai,

China).

100

FeCl3·6H2O, FeCl2·4H2O, dibutyl phthalate (DBP), benzoyl peroxide (BPO), styrene,

101

polyvinylpyrrolidone (PVP), and sodium dodecyl sulfate (SDS) were obtained from

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Tianjin Chemical Reagents Company (Tianjin, China). Atrazine, propazine, simazine

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and terbuthylazine were obtained from Binzhou Agricultural Technology Co., Ltd.

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(Shandong, China). Acetonitrile (ACN) used as HPLC mobile phase was from Merck

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(Darmstadt, Germany). Ultra-pure water (18.2 MΩ·cm-1 specific resistance) was

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self-prepared in laboratory by Pall Cascada water system (New York, USA).

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Stock solutions containing 100 mg·L-1 of four kinds of triazines were prepared by

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dissolving the standards into ACN. Diluting the stock solutions with ACN to prepare

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working solutions. Both stock and working solutions were stored in refrigerator.

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Instruments and Analytical Methods. Transmission electron microscopy (TEM;


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JEOL, JEM-1230, Japan) and scanning electron microscope (SEM, Hitachi S-4800

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FE-SEM) were employed for morphological observation. A vibration sample

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magnetometer (VSM7307, Lake Shore, USA) was employed for the measurement of

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magnetization in at room temperature. HPLC equipped with a C18 ODS column (250

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mm×4.6 mm, 5 mm) and UV detector (Elite Instrument Inc., China) was used for

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quantitative analysis of each pollutants with conditions for trizaines as follows:

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mobile phase, ACN: water (48: 52, v/v) with flow rate at 1.0 mL·min-1; injection

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volume 20 µL with UV detection at 220 nm; room temperature.

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Preparation of M-H-MIPs. The process for preparation of M-H-MIPs was

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composed of the following steps: preparation of H-MIPs; epoxide ring opening and

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immobilization of Fe3O4 on H-MIPs. First, H-MIPs were prepared using seed

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swelling polymerization method as our previous work11 with minor modification. The

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specific process was as follows: 0.2 g monodispersed polystyrene seeds prepared by

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dispersion polymerization, 0.125 g SDS and 50 mL water were mixed to form

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homogenous emulsion, then followed by three steps swelling. 0.7 mL DBP was used

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for the first step swelling, followed by the second step swelling with the mixture of 10

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mL toluene, 0.344 mL MAA, 0.413 mL GMA and 0.215g atrazine, then the third step

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swelling by 60 mg BPO and 4.0 mL DVB. After three-step swelling, polymerization

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was carried out at 80 oC for 1 day. The polymers were washed with dichloromethane

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and methanol to remove polystyrene seeds and template atrazine. Finally, H-MIPs

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were prepared.

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Then epoxide rings on the surface of H-MIPs were opened with the help of



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perchloric acid. The specific process was as follows: 400 mg H-MIPs prepared above

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were poured into 25 mL 10% perchloric acid water solution followed by stirring at 25

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o

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obtained.

C for 24 h. After filtration, washing and drying, H-MIPs with 1,2-diol groups were

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At last, M-H-MIPs were prepared by coprecipitation of Fe2+ and Fe3+ on the surface

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of H-MIPs with 1,2-diol groups according to previous literatures20. Briefly, 200 mg

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H-MIPs with 1,2-diolgroups, 0.01 mmol FeCl2·4H2O and 0.02 mmol FeCl3·6H2O

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were charged into 20 mL methanol/water (1/4, v/v) solution. The mixture was

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dispersed homogeneous with the help of ultrasonic wave and then purged with N2 to

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remove O2. After increasing the temperature to 80 oC, 3 mL NH3·H2O was dropwise

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added, and the reaction was carried out at 80 oC in N2 atmosphere for 1 h under

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continuously stirring. At last, M-H-MIPs were collected magnetically, washed with

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ethanol and water repeatedly, and then dried to constant weights. Using the same

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procedures, magnetic hollow porous non imprinted polymers (M-H-NIPs) were

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prepared but without template atrazine.

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Binding Property of the M-H-MIPs. Static adsorption, kinetic adsorption and

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selective binding were carried out to characterize the specific molecular binding

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properties of M-H-MIPs. For static adsorption capacity, 20 mg M-H-MIPs particles

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were dispersed uniformly into 2.0 mL atrazine/ACN solution varying from 0.5 to 70

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mg·L−1. After adsorption at room temperature for 1 day, the mixture was separated

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and supernatant was detected by HPLC. The static binding capacity can be calculated

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using the initial and final concentration of atrazine. Meanwhile, the dynamic binding


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cure was tested by detection the temporal amount of atrazine when fixed the initial

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concentration of atrazine at 50 mg·L−1. Selectivity adsorption ability was evaluated

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using simazine, propazine and terbuthylazine as structural analogs while furazolidone

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and carbendazim as control.

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Analysis of Real Food Samples by Dispersive Solid Phase Extraction.

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M-H-MIPs were applied to extract four triazines, including atrazine, propazine,

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simazine and terbuthylazine, from corn, wheat and soybean samples by dispersive

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solid phase extraction (DSPE) method. Dried corn, wheat and soybean samples were

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purchased from local market and prepared as previous method21. Briefly, 50 g crushed

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corn, soybean or wheat and 100 mL ACN were mixed and incubated for 8 h in order

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to retrieve triazines herbicide. As no triazines was detected from those three samples,

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then spiked experiment was carried out. Nine spiked samples were prepared by

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adding the mixture standards of atrazine, simazine, propazine and terbuthylazine into

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corn, wheat and soybean extraction solutions with the final concentration at 1.0, 5.0

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and 50 µg·L-1, respectively. The specific process for DSPE was as follows. After

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condition with 5.0 mL methanol, 600 mg M-H-MIPs were added into 100 mL spiked

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solution followed by ultrasound-assisted extraction for 15 min. Then M-H-MIPs were

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separated and washed with 5.0 mL ACN before eluted by 5.0 mL 1% acetic acid

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acidified methanol. The eluate was concentrated with the help of nitrogen blowing,

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and redissolved into 0.2 mL ACN for further HPLC analysis.

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RESULTS AND DISCUSSION

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Preparation and Characterization of M-H-MIPs. Hollow polymers have



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significant advantages in increasing binding capacity and accelerating mass transfer.

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Magnetic property is facility for rapid and efficient separation. So in this work, we

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prepared magnetic hollow MIPs in order to integrate the separation ability of Fe3O4

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particles and faster mass transfer ability of hollow polymer into one system. Unlike

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embedding Fe3O4 into MIPs as core, Fe3O4 nanoparticles were immobilized on the

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surface of H-MIPs by in situ growth method. The synthesis procedure for atrazine

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imprinted M-H-MIPs was illustrated in Figure 1, which involved three successive

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steps: H-MIPs preparation, epoxide ring opening and Fe3O4 immobilization. First,

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H-MIPs were prepared by multi-step swelling polymerization as our previous work11,

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using polystyrene as seeds, toluene as porogen, atrazine as template, MAA as

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functional monomer and DVB as cross-linker. To facilitate the growth of magnetic

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nanoparticles on the surface of H-MIPs, GMA was used as co-functional monomer.

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Epoxy bond opening with the help of HClO4 provided a hydroxyl-rich

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microenvironment on the surface of H-MIPs, in which Fe3O4 were prior to growth.

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Then the last step was immobilization of Fe3O4 by in situ growth method based on the

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cooperation of Fe3+ and Fe2+ under base medium in N2 atmosphere.

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The key point throughout the preparation process is the amount of GMA. Little

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GMA would result in insufficient hydroxyl to induce the growth of the magnetic

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particles on the surface of hollow MIPs. On the contrary, too much GMA would cause

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excessive magnetic particles, and the binding capacity of M-H-MIPs would be

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reduced. In this work, optimum amount of GMA was examined using magnetic

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property and binding capacity as evaluation index. The amount of functional


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monomer MAA was fixed as 0.344 mL while changing MAA/GMA (v/v) ratio from 1:

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0.2 to 1: 2.0. It was found that when the ratio is less than 1: 0.6, magnetic particles

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were difficult to grow on the surface of hollow MIPs. When the ratio is greater than 1:

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1.5, there would be a large number of magnetic particles covering the surface of the

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polymer, which resulted in lower binding capacity. Finally, the optimum ratio of

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MAA/GMA was 1: 1.2.

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The preparation procedure was estimated by TEM and SEM. Figure 2 showed the

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morphology of polystyrene seeds, H-MIPs and M-H-MIPs. Regular sphere

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polystyrene seeds were monodispersed with diameter about 850 nm. Hollow structure

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can be formed by multi-step swelling polymerization, which were clearly indicated by

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Fig. 2B. The diameter of H-MIPs was about 1.8 µm and the surface of H-MIPs was

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smooth. After immobilizing Fe3O4 nanoparticles, the surface of M-H-MIPs became

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rough and the diameter displayed a slight increase. TEM and SEM images provided a

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powerful evidence to confirm the successfully preparation process.

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For the H-MIPs and M-H-MIPs, the surface area was studied using the BET

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adsorption method. The BET surface area of M-H-MIPs was about 357 m2·g-1, which

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was higher than H-MIPs of 271 m2·g-1. The larger BET surface area probably resulted

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from the magnetic nanoparticles immobilized on the rough surface of M-H-MIPs.

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The magnetic separation ability of M-H-MIPs was confirmed by magnetic

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hysteresis loops and the dispersion/agglomeration process, which were illustrated in

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Figure 3. The magnetic saturation of M-H-MIPs was 2.32 emu·g-1, confirming the

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successful immobilization of magnetic nanoparticles. When applied an external



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magnetic field on the outer side wall of the vials, the homogeneously dispersed

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M-H-MIPs could adhere to the wall of vials quickly and lead to the formation of clear

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and transparent solution. The results showed that M-H-MIPs obtained in this work

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could be separated and collected in a simply and effectively way.

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Binding Properties of M-H-MIPs. Binding capacity and binding rate are key

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indexes to evaluate the performances of MIPs. So in this work, binding property

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including static binding, dynamic binding and selective binding of M-H-MIPs were

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evaluated in detail. First, static adsorption experiments were executed to measure the

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adsorption capacities of M-H-MIPs using H-MIPs and M-H-NIPs as control, and the

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results were displayed in Figure 4A. From Figure 4A we can see that the adsorption

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capacity of M-H-MIPs and H-MIPs increased quickly with the increasing of atrazine

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concentration until the concentration reach to 60 mg·L−1, where the adsorption

233

capacity reached an equilibrium. We also can see that the binding capacity of H-MIPs

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was slight higher than M-H-MIPs. This was because magnetic particles didn’t

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contribute to binding target molecules. None specific recognition site for atrazine was

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form in NIPs because no template was used during the preparation process, so

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M-H-NIPs displayed lower binding capacity than corresponding M-H-MIPs. The

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adsorption capacity of M-H-MIPs (1.69 mg·g−1) was about 4 fold over that of

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M-H-NIPs (0.37 mg·g−1) after adsorption equilibrium. The result confirmed the

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specific recognition ability of MIPs.

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The binding isotherms of MIPs and NIPs were evaluated using Langmuir,

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Freundlich or Langmuir -Freundlich adsorption isotherm models, The model fitting


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results revealed that Langmuir isotherm model (Eq. 1) with an R2 value of 0.9354

244

yielded the better fitting than the Freundlich isothermal equation (R2=0.8123) and the

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Langmuir-Freundlich equation (R2=0.7234). According to Langmuir adsorption

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model, Qmax, the maximum binding capacity, were 3.70 mg·g−1, 3.22 mg·g−1 and 0.52

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mg·g−1 for H-MIPs, M-H-MIPs and M-H-NIPs, respectively.

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Ce 1 1 = Ce + Qe Q max KlQ max

(1)

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Scatchard analysis was also often employed to measure the binding isotherms. In

250

the light of Scatchard equation (Eq. 2), Scatchard plots were calculated and displayed

251

in Figure 4B. Consequently, the equilibrium dissociation constants Kd and maximum

252

binding capacities Qmax were calculated. Qmax for H-MIPs, M-H-MIPs and M-H-NIPs

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were 2.81 mg·g-1, 2.38 mg·g-1 and 0.51 mg·g-1, respectively. Kd were 14.99 mg·L-1,

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19.08 mg·L-1 and 23.31 mg·L-1, respectively.

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Q Ce

=

Qmax Q − Kd Kd

（2）

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The mass transfer properties of MIPs and NIPs can be assessed by dynamic binding

257

experiments and the kinetic curves of atrazine adsorption on M-H-MIPs, H-MIPs and

258

M-H-NIPs were illustrated in Figure 4B. It can be clearly seen that higher adsorption

259

time would lead to the greater adsorption capacity, and the rule was valid within 1h.

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1h was enough for M-H-MIPs to reach the dynamic adsorption equilibrium,

261

demonstrating the fast adsorption process. In comparison, MIPs prepared by living

262

precipitation polymerization22 and surface imprinting method23 would take 7 h and 5 h,

263

respectively, to reach adsorption equilibrium in our previous work. Therefore, hollow

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porous structure of M-H-MIPs facilitated the diffusion of targets to recognition sites.



265

Elovich, Pseudo-first-order, Pseudo-second-order and intraparticle diffusion kinetic

266

models were employed to fit the dynamic binding and the results were displayed in

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Figure 4. The result evidenced that pseudo-second-order model, expressed as Eq. 3,

268

best fitted the dynamic adsorption with R2 higher 0.995. In the equation, Qe is the

269

equilibrium adsorption amount, Qt is the instantaneous adsorption amount at time t

270

and k2 is the adsorption constant. According to pseudo-second-order model, Qe was

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2.17 mg·g-1, 1.86 mg·g-1 and 0.55 mg·g-1 for H-MIPs, M-H-MIPs and M-H-NIPs,

272

respectively, which agreed with the Qe of 1.9 mg·g-1, 1.53 mg·g-1 and 0.35 mg·g-1

273

from the experimental results when the initial concentration of atrazine fixed as 50

274

mg·L-1. Thus, the dynamic adsorption followed the pseudo-second-order model.

275

t 1 t = + 2 Qt k2Qe Qe

(3)

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The cross-reactivity of the M-H-MIPs was assessed by selective binding

277

experiment while using M-H-NIPs as control. Simazine, propazine and terbuthylazine

278

were used as structural analogs while carbendazim and furazolidoneas as control. The

279

structure of involved molecules were displayed in Figure 4E. Imprinted factor (IF),

280

which defined as the ratio of QMIP to QNIP, was adopted to evaluate the selectivity of

281

the as-prepared MIPs. From Fig. 4D we can see that M-H-MIPs exhibited higher

282

binding capacity for the four triazine derivatives than the two structurally unrelated

283

compounds. It’s well known that triazine herbicides share similar structures, which

284

was hard to distinguish even using antibodies. Thus the cavities for atrazine also can

285

recognize simazine, propazine and terbuthylazine. The result implied that atrazine

286

imprinted M-H-MIPs can recognize the family of triazines. It’s a good message for


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sample pretreatment because tedious work can be avoid to prepare a series of MIPs.

288

For carbendazim and furazolidone, the molecular structure were less resemblance to

289

atrazine, which resulted in the lower binding capacity. When compared the adsorption

290

capacity of six compounds onto M-H-NIPs, we can see that the values were very

291

close and lower than those in M-H-MIPs. The adsorption of M-H-NIPs was all

292

non-selective because there were no tailor-made selective recognition sites. IF,

293

calculated from Fig. 4D, ranged from 5.1 to 5.6 for simazine, propazine and

294

terbuthylazine, while the value for carbendazim and furazolidone was lower than 1.2.

295

The higher IF implied the higher selectivity property of atrazine imprinted M-H-MIPs

296

for triazine herbicides.

297

From binding experiments we can see that M-H-MIPs can achieve rapid and

298

convenience separation while they enjoy faster mass transfer property. Meanwhile,

299

atrazine imprinted M-H-MIPs displayed significant class selective recognition ability

300

for the family of trazines herbicides. So M-H-MIPs could be an ideal sorbent to

301

extract triazines from complicated samples.

302

Analytical Performance of DSPE Based on M-H-MIPs. M-H-MIPs were used as

303

adsorption sorbent to carry out dispersive solid phase extraction (DSPE) of four

304

triazine herbicides from real food samples in order to evaluate the feasibility of the

305

obtained M-H-MIPs. Various factors involved in the whole DSPE procedure

306

(condition, extraction, separation, washing and eluting), such as the amount of

307

M-H-MIPs, extraction time and elution solvent, etc., were studied in detail in order to

308

get the optimal extraction condition.



309

The dosage of M-H-MIPs played an important role in extraction process because

310

insufficient adsorption sites resulting from low amount of M-H-MIPs would lead to

311

lower extraction efficiency and long adsorption time. In this work, changing the

312

amount of M-H-MIPs from 300 to 900 mg while the concentration of trazines fixed at

313

100 µg·L-1 and extraction time at 30 min, the effect of amount of M-H-MIPs on

314

extraction efficiency was studied. The results (Figure S1) indicated that the recoveries

315

increased with the increasing of M-H-MIPs before reach to a plateau of 95% when 0.6

316

g M-H-MIPs were used. However, further increasing the amount of M-H-MIPs did

317

not bring significant increase in recoveries. Then as another important factor,

318

extraction time was optimized. From Figure S2 we can see that extraction efficiency

319

increased from 50.3% to 95.4% when ultrasound-assisted extraction time increased

320

from 5 to 15 min. Keeping increasing extraction time did not bring significant

321

improvement in recovery. So 15 min was enough for ultrasound-assisted extraction.

322

Another important affecting factor was the elution solvent. In addition to methanol

323

and ACN, acidified methanol were tested as eluting solvents. The result showed that

324

the elution efficiency of acid methanol was higher than other solvent (Figure S3) and

325

there was no significant difference for 90:10 and 99:1.0 (methanol: acetic acid).

326

Finally, 5×1mL of a mixture of methanol/acetic acid (99/1.0, v/v) was selected as

327

eluting solvent to promise the high recoveries of four triazine herbicides.

328

Under the above-identified optimum conditions, the linear range and limits of

329

detection (LOD) of the analytical method were further investigated and the results

330

were shown in Table 1. For the method of M-H-MIPs-DSPE coupled with HPLC, a


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good linearity was derived in the range of 0.5-200 µg·L-1 for atrazine, simazine and

332

1.0-200 µg·L-1 for propazine and terbuthylazine with correlation coefficients of

333

0.9992, 0.9978, 0.9959 and 0.9962, respectively. LOD, calculated as 3S/N, were 0.16,

334

0.23, 0.31 and 0.39 µg·L-1 for atrazine, simazine, propazine, terbuthylazine,

335

respectively. Replicate analyses at spiked concentration of 100 µg·L-1 were performed

336

on the same day and on six different days to determine the intraday precision and

337

interday precision given by the relative standard deviations (RSD). The RSD of

338

intraday was 3.2−5.6% and 3.6−4.9% for interday reproducibility. Therefore, it was

339

demonstrated that this method can be applied to accurate and sensitive quantitative

340

determination of triazine in real samples.

341

To verify the recyclability of M-H-MIP-DSPE, regeneration (adsorption/

342

desorption) cycles were conducted. After M-H-MIPs were used to enrich four

343

triazines herbicides, the material could be regenerated by washing with 5 mL

344

methanol/acetic acid (90/10, v/v), 5 mL methanol and 5 mL ACN. After experienced

345

repeated 5 times regeneration, M-H-MIPs displayed good reusability and still kept the

346

high recovery with a loss of average recovery less than 5.0 % (Table S1). The result

347

indicated the stability of M-H-MIPs.

348

The methodology was applied to extract trazines from corn, wheat and soybean

349

samples. Initial analysis confirmed that those three samples were free of triazine

350

herbicides. So spiking procedure was carried out. HPLC chromatography (Figure S4)

351

for the three samples showed that four triazine compounds can be remarkably

352

concentrated while the interference substances in the real samples could be removed



353

after selective extraction. Although there were still some impurities after treated by

354

M-H-MIP-DSPE, they had the least impact on the quantitative determination.

355

Recovery and RSD was employed to evaluate the accuracy and the precision of the

356

method, respectively. DSPE procedure for spiked samples at three concentrations (1.0,

357

5.0 and 50 µg·L-1) in different samples were carried out and the results were displayed

358

in Table 2. The recoveries of atrazine, simazine, propazine and terbuthylazine with

359

M-H-MIP-DSPE for the spiked corn, wheat and soybean were 82.14−101.69%,

360

81.22−98.42%, 81.35−97.75% and 80.62−97.78%, respectively. The RSDs were

361

1.9−4.0%, 2.6−4.6%, 2.4−4.6% and 3.2−5.2%, respectively.

362

Furthermore, in order to demonstrate the suitability of a method for analysis of

363

real-life samples, the method was applied to test positive samples that are

364

contaminated with triazines. The corn and soybean samples contaminated ranging

365

between 5 and 20 µg·kg-1 were provided by Food Quality Supervision Bureau of

366

Linyi. The samples were analyzed using M-H-MIPs-DSPE and the results were

367

compared with those obtained from Food Quality Supervision Bureau of Linyi using

368

the National Standard Method (Table 3). From Table 3 we can see that the values in

369

our method were agree well with those obtained by accredited method. The results

370

demonstrated that M-H-MIPs-DSPE coupled with HPLC was an efficient and

371

effective methodology for selective extraction and sensitive assessment of multiple

372

triazine herbicides at a very low concentration.

373

In summary, novel M-H-MIPs were prepared by multi-step swelling polymerization

374

followed by in-situ growth of magnetic Fe3O4 nanoparticles on the surface of hollow


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375

MIPs. M-H-MIPs showed some attractive characteristics, such as higher binding

376

capacity, faster binding kinetics, and quicker separation. M-H-MIPs were successfully

377

applied to selective purify and concentrate triazine herbicides from real samples. The

378

method proposed in this work was proved to be a simple and efficient approach for

379

selective and sensitive detection of triazines from complicated food matrices.

380 381

ACKNOWLEDGEMENTS

382

We thank NSFC (NO. 21307052), the Natural Science Foundation of Shandong

383

Province of China (ZR2013BL006).

384 385

REFERENCES

386

(1) Blasco, C.; Picó, Y. Development of an improved method for trace analysis of quinolones in

387

eggs of laying hens and wildlife species using molecularly imprinted polymers. J. Agric. Food

388

Chem. 2012, 60, 11005–11014.

389

(2) Liu, S.; Yan, H.Y.; Wang, M.Y.; Wang, L.H. Water-compatible molecularly imprinted

390

microspheres in pipette tip solid-phase extraction for simultaneous determination of five

391

fluoroquinolones in eggs. J. Agric. Food Chem. 2013, 61, 11974–11980.

392

(3) Ma, J.B.; Qiu, H.W.; Rui, Q. H.; Liao, Y.F.; Chen, Y.M.; Xu, J.; Zhan, P.P.; Zhao, Y.G. Fast

393

determination of catecholamines in human plasma using carboxyl-functionalized magnetic-carbon

394

nanotube molecularly imprinted polymer followed by liquid chromatography-tandem quadrupole

395

mass spectrometry. J. Chromatogr. A 2016, 1429, 86–96.

396

(4) Altintas, Z.; Gittens, M.; Guerreiro, A.; Thompson, K.A.; Walker, J.; Piletsky, S.; Tothill, I.E.

397

Detection of waterborne viruses using high affinity molecularly imprinted polymers. Anal. Chem.

398

2015, 87, 6801–6807.

399

(5) Wang, J.X.; Gao, L.; Han, D.L.; Pan, J.M.; Qiu, H.; Li, H.J.; Wei, X.; Dai, J.D.; Yang, J.H.;

400

Yao, H.; Yan, Y.S. Optical detection of λ-cyhalothrin by core–shell fluorescent molecularly



401

imprinted polymers in chinese spirits. J. Agric. Food Chem. 2015, 63, 2392–2399.

402

(6) Ahmad, R.; Griffete, N.; Lamouri, A.; Felidj, N.; Chehimi, M.M.; Mangeney, C.

403

Nanocomposites of gold nanoparticles@molecularly imprinted polymers: chemistry, processing,

404

and applications in sensors. Chem. Mater. 2015, 27, 5464–5478.

405

(7) Xu, S.F.; Lu, H.Z.; Chen, L.X.; Wang, X.C. Molecularly imprinted TiO2 hybridized magnetic

406

Fe3O4 nanoparticles for selective photocatalytic degradation and removal of estrone. RSC Adv.

407

2014, 4, 45266–45274.

408

(8) Shen, X.T.; Zhu, L.H.; Yu, H.W.; Tang, H.Q.; Liu, S.S.; Li, W.Y. Selective photocatalysis on

409

molecular imprinted TiO2 thin films prepared via an improved liquid phase deposition method.

410

New J. Chem. 2009, 33, 1673–1679.

411

(9) Bi, X.D.; Liu, Z. Facile preparation of glycoprotein-imprinted 96-well microplates for

412

enzyme-linked immunosorbent assay by boronate affinity-based oriented surface imprinting. Anal.

413

Chem. 2014, 86, 959–966.

414

(10) Gao, D.M.; Zhang, Z.P.; Wu, M.H.; Xie, C.G.; Guan, G.J.; Wang, D.P. A surface functional

415

monomer-directing strategy for highly dense imprinting of tnt at surface of silica nanoparticles. J.

416

Am. Chem. Soc. 2007, 129, 7859–7866.

417

(11) Xu, S.F.; Chen, L.X.; Li, J.H.; Qin, W.; Ma, J.P. Preparation of hollow porous molecularly

418

imprinted polymers and their application to solid-phase extraction of triazines in soil samples. J.

419

Mater. Chem. 2011, 21, 12047–12053.

420

(12) Zhang, Z.; Xu, S.F.; Li, J.H.; Xiong, H.; Peng, H.L.; Chen, L.X. Selective solid phase

421

extraction of sudan I in chilli sauce by single hole hollow molecularly imprinted polymers. J.

422

Agric. Food Chem. 2012, 60,180–187.

423

(13) Jung, B.M.; Kim, M.S.; Kim W.J.; Chang, J.Y. Molecularly imprinted mesoporous silica

424

particles showing a rapid kinetic binding. Chem. Commun. 2010, 46, 3699–3701.

425

(14) Lu, H.Z.; Xu, S.F.; Mesoporous structured estrone imprinted Fe3O4@SiO2@mSiO2 for highly

426

sensitive and selective detection of estrogens from water samples by HPLC. Talanta, 2015, 144,

427

303–311.

428

(15) Ambrosini, S.; Beyazit, S.; Haupt, K.; Bui, B.T.S. Solid-phase synthesis of molecularly

429

imprinted nanoparticles for protein recognition. Chem. Commun. 2013, 49, 6746–6748.

430

(16) Xu, J.J.; Ambrosini, S.; amahkar, E.; Rossi, T.; Haupt, K.; Bui, B.T.S. Toward a universal


Page 20 of 29

Page 21 of 29


431

method for preparing molecularly imprinted polymer nanoparticles with antibody-like affinity for

432

proteins. Biomacromolecules, 2016, 17, 345–353.

433

(17) Chen, J.X.; Lei, S.; Xie, Y.Y.; Wang, M.Z.; Yang, J.; Ge, X.W. Fabrication of

434

high-performance magnetic lysozyme-imprinted microsphere and its NIR-responsive controlled

435

release property. ACS Appl. Mater. Interfaces 2015, 7, 28606–28615.

436

(18) Xu, S.F.; Lu, H.Z.; Zheng, X.W.; Chen, L.X. Stimuli-responsive molecularly imprinted

437

polymers: versatile functional materials. J. Mater. Chem. C 2013, 1, 4406–4422.

438

(19) Xu, C.G.; Shen, X.T.; Ye, L. Molecularly imprinted magnetic materials prepared from

439

modular and clickable nanoparticles, J. Mater. Chem., 2012, 22, 7427–7433.

440

(20) Li, H.; Hu, X.; Zhang, Y.P.; Shi, S.Y.; Jiang, X.Y.; Chen, X.Q. High-capacity magnetic hollow

441

porous molecularly imprinted polymers for specific extraction of protocatechuic acid. J.

442

Chromatogr. A. 2015, 1404, 21–27.

443

(21) Hu, X.G.; Hu, Y.L.; Li, G.K. Development of novel molecularly imprinted solid-phase

444

microextraction fiber and its application for the determination of triazines in complicated samples

445

coupled with high-performance liquid chromatography. J. Chromatogr. A 2007, 1147, 1–9.

446

(22) Xu, S.F.; Li, J.H.; Chen, L.X. Molecularly imprinted polymers by reversible

447

addition-fragmentation chain transfer precipitation polymerization for preconcentration of atrazine

448

in food matrices. Talanta 2011, 85, 282–289.

449

(23) Xu, S.F.; Li, J.H.; Chen, L.X. Molecularly imprinted core-shell nanoparticles for

450

determination of trace atrazine by reversible addition-fragmentation chain transfer surface

451

imprinting. J. Mater. Chem. 2011, 21, 4346–4351.



Figure caption Figure 1 The process of preparation of M-H-MIPs by in situ growth method. Figure 2 SEM (upper) and TEM (below) images of M-H-MIPs preparation process. A. polystyrene, B. H-MIPs, C. M-H-MIPs.

Figure 3 Magnetic hysteresis loops of M-H-MIPs, the insets show the dispersion and agglomeration process of the M-H-MIPs nanoparticles.

Figure 4 Binding isotherms of MIPs for atrazine in ACN, which including static adsorption experiment (A), Scatchard analysis(B), dynamic binding experiment (C), selective binding experiment (D) and chemical structure for atrazine, simazine, propazine, terbuthylazine, carbendim and

furazolidone(E). Experimental conditions

for static adsorption experiment and Scatchard analysis: V= 2.0 mL; mass of polymer, 20 mg; adsorption time, 24 h. Experimental conditions for dynamic binding experiment: V= 2.0 mL; C0= 50 mg L-1; mass of polymer, 20 mg. Experimental conditions for selective binding experiment: polymer, 20 mg; C0 = 50 mg L-1; V= 2.0 mL; adsorption time, 24 h; room temperature.


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Figure 1

Figure 2



Figure 3


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Figure 4




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Table 1 Linear Relations, Detection Limits and Relative Standard Deviations (RSD%, n=6) for Determination of the Four Triazines. Linear range Sample

(µg·L-1)

2

R

LOD

RSD (100 µg·L-1)

(µg·L-1)

Interday

Intraday

Atrazine

0.5-200

0.9992

0.16

3.2

3.6

Simazine

0.5-200

0.9978

0.23

3.9

4.2

Propazine

1.0-200

0.9959

0.31

4.2

4.4

Terbuthylazine

1.0-200

0.9962

0.39

5.6

4.9



Page 28 of 29

Table 2 Recoveries and Relative Standard Deviations (RSD, %) Obtained from Analysis of Corn, Wheat and Soybean Samples Spiked with Four Kinds of Triazines.

Recovery, mean±RSD (%) Sample

Compound

1.0 µg·L-1

5.0 µg·L-1

50.0 µg·L-1

Atrazine

82.14±3.6

94.58±4.0

99.87±3.2

Simazine

81.22±4.3

92.31±3.6

96.21±4.6

Propazine

81.35±4.2

90.65±4.3

95.37±4.3

Terbuthylazine

80.62±3.4

91.12±5.2

93.19±3.9

Atrazine

86.39±3.8

94.63±3.6

101.69±2.8

Simazine

84.19±4.1

94.39±4.4

98.42±2.6

Propazine

85.20±3.9

91.88±4.6

97.75±2.9

Terbuthylazine

82.57±5.1

92.78±3.8

97.78±3.3

Atrazine

84.64±2.9

93.36±2.6

98.85±1.9

Simazine

83.54±3.2

90.59±3.1

97.78±3.1

Propazine

83.56±3.7

92.17±2.4

96.05±3.4

Terbuthylazine

81.87±4.0

91.06±3.4

95.03±3.2

Corn

Wheat

Soybean


Page 29 of 29


Table 3 Results±RSD% of the Analysis of Positive Corn and Soybean Samples Using M-H-MIPs-DSPE and National Standard Method.

Sample

M-H-MIPs-DSPE

National Standard method

Atrazine (µg·kg-1)

Simazine (µg·kg-1)

Atrazine(µg·kg-1)

Simazine (µg·kg-1)

Corn 1

5.66±3.7

ND

5.46±2.9

ND

Corn 2

15.98±3.1

5.40±3.5

16.32±2.6

5.23±1.9

Soybean 1

15.48±2.9

5.32±3.6

15.23±3.2

5.21±2.9

Soybean 2

ND

8.65±3.1

ND

8.74±2.7

ND: not detected. RSD%, n=3.


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