Conjugated Microporous Polymers with Built-In Magnetic

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Conjugated Microporous Polymers with Built-in Magnetic Nanoparticles for Excellent Enrichment of Trace Hydroxylated Polycyclic Aromatic Hydrocarbons in Human Urine Langjun Zhou, Yuling Hu, and Gongke Li Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b01708 • Publication Date (Web): 10 Jun 2016 Downloaded from http://pubs.acs.org on June 12, 2016

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Analytical Chemistry

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Conjugated Microporous Polymers with Built-in Magnetic

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Nanoparticles for Excellent Enrichment of Trace Hydroxylated

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Polycyclic Aromatic Hydrocarbons in Human Urine

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Langjun Zhou, Yuling Hu*, Gongke Li*

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School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou, 510275, China

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* Corresponding author: Yuling Hu, Gongke Li

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Tel. : +86-20-84110922

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Fax : +86-20-84115107

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E-mail : [email protected]

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[email protected]

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ACS Paragon Plus Environment


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Conjugated microporous polymers (CMPs), linked by covalent bond to form

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ABSTRACT:

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extension of aromatic ring skeleton, are microporous materials characterized by high

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conjugated structure and high stability. The present study reported on a novel strategy about

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the synthesis of CMPs with built-in magnetic nanoparticles for excellent enrichment of trace

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hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) in human urine. We modified

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Fe3O4 nanoparticles with boronic acid groups and then reacted with reactive monomers of

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polyphenylene conjugated microporous polymer (PP-CMP) to anchor the magnetic

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components in the PP-CMP framework. Chemical bonding between Fe3O4 nanoparticles and

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PP-CMP networks, together with equally firm covalent linkage and rigidity of PP-CMP

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network, endows the magnetic PP-CMP with remarkable chemical stability and durability,

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even in harsh conditions. Magnetic PP-CMP has the characteristic of both high conjugacy,

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highly porous structure and magnetism, which makes it become an ideal magnetic adsorbent

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for trace analytes with aromatic conjugation structure. Adsorption mechanism of OH-PAHs on

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magnetic PP-CMP was investigated and told that hydrophobic interaction was important for

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the contribution of interaction between adsorbents and target analytes, together with the

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assistance of π-π stacking interaction. For the application, the magnetic PP-CMP was used for

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the enrichment of trace OH-PAHs in human urine of both smokers and non-smokers in

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combination with high-performance liquid chromatography with fluorescence detection

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(HPLC-FLD). It showed good selectivity and excellent sensitivity to these OH-PAHs. Their

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detection limits were low and in the range of 0.01-0.08 µg·L-1. The OH-PAHs were detected

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with different amounts from 0.054 to 0.802 µg·L-1 in urine samples from smokers and

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non-smokers. The recoveries were found to be 76.0%-107.8%. The results indicate that the

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magnetic PP-CMP offers an efficient enrichment method for trace OH-PAHs in human urine. 2


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INTRODUCTION

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Porous materials have attracted great attention over the past decade on account of their

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outstanding performance in sample preparation.1-4 Among them, metal-organic frameworks

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(MOFs), characterized by high surface area, easily regulative pore structure, high-adsorption

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ability, excellent thermal stability and easily functionalized modification for target analytes,

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have developed profoundly in the field of enrichment5, 6 and separation.7, 8 Although MOFs

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play an important role in sample preparation, there are still some limitation caused by their

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bonding type. Because coordination bonds are the linkage mode between linking organic

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ligands and metal moieties of MOFs, many MOFs are lacking in chemical stability when they

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are exposed to solvents, especially in moisture. Thus, this weak linkage limits the practical

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application value of MOFs.9, 10

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Thus, pure organic frameworks such as microporous organic polymers (MOPs), which

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comprised of light, nonmetallic elements and generated by linkage of organic polymerizable

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monomer building blocks, are supposed to be a new generation of microporous materials.

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Conjugated microporous polymers (CMPs) are a category of MOPs with conjugated structure,

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which are linked by multiple carbon-carbon bonds or aromatic benzene ring to form a class of

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skeleton materials with extension of conjugated system, possessing large surface area,

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excellent stability, accurately tunable nanopore size.11 Their outstanding characters are

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interesting for multifarious applications, such as gas adsorption and storage,12-14

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chemosensors,15-17 heterogeneous catalysis,18-20 encapsulation of chemicals,21-23 light

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emitters.24-26 Compared with MOFs, CMPs have more excellent stability, which can stably

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exist under harsh conditions, including in acid, alkali, organic solvents, moisture and high

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temperature. As a consequence, we can suppose that CMPs have the potential to remedy the 3



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limitation of MOFs when they need to be used in the above-mentioned harsh conditions. In

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addition, the large conjugated structure in CMPs network makes CMPs become an ideal

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adsorbent for trace analytes with aromatic conjugation structure.

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Owing to similar porous structure to MOFs and better stability, CMPs must do well in

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separation and enrichment for trace analytes from various sample matrixes. But as far as we

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know, up to now, there are just a few articles describing CMPs used in analytical chemistry,

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which focus on chemosensors.15-17 Jiang27 reported the first example of CMP applied as a

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chemosensor, which displayed increased detection sensitivity and rapid detection ability to

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arenes when exposed to their vapous. Cao28 reported two CMPs named COP-3 and COP-4,

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which were highly sensitive to nitroaromatic explosives with a low detection limit of less than

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1 mg·L-1. Recently, our group have reported a microporous organic polymer (MOP) material

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SNW-1 coating,9 which exhibited excellent enrichment of trace volatiles, was fabricated by

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multilayer interbridging strategy. However, the exploration of CMPs as excellent adsorbents

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for enrichment remains undeveloped.

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Recently, CMP composite materials involving diverse characteristics in one material

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have been synthesized, which gives rise to a noteworthy improvement of properties such as

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catalytic activity or photo-luminescence. For instance, Core-shell conjugated microporous

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polymers, combining two different kinds of CMPs, were reported by Jiang.24 The Core-shell

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CMP allowed the light emissions to be colour-tunable in a controllable way. CMPs have been

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doped with Pd nanocrystals, leading to extraordinarily high catalytic activity, excellent

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recovery and reusability. However, compared with the flexibility of organic function, fewer

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kinds of inorganic nanoparticles can be anchored to the CMP. The main reasons for this

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phenomenon might be: (1) CMPs have a tendency to gather together leading to the uneven 4


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distribution of inorganic nanoparticles on the surface of the CMP block mass; (2) it is too

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small for CMP networks with micropore structure to accommodate inorganic nanoparticles.

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Magnetic materials are widely used in solid-phase extraction (SPE) because of their

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outstanding convenience for retrieval from sample matrix.29-31 The design and synthesis of

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magnetic CMPs are especially desirable. As we know, there are several method for synthesis

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of magnetic composites materials, such as embedding,3 layer-by-layer,32 encapsulation33 and

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physical mixing.34 Guo35 reported a magnetic conjugated nanoporous polymer colloid

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(Fe3O4@CNPC) synthesized by embedding method. However, for the reasons given above, it

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is difficult for magnetite (Fe3O4) nanoparticles to be anchored to the CMP. The available sizes

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for Fe3O4 nanoparticles are generally more than 10 nm, while the popular pore sizes of the

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CMP range from 1-5 nm. Therefore, the method for synthesizing magnetic CMP composites

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materials needs prompt development. Thereinto, the linkage strategy between Fe3O4

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nanoparticles and CMP network, especially the modification strategy to Fe3O4 nanoparticles,

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remains a difficult but particularly important part for the synthesis of magnetic CMPs.

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Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic compounds, and cancers in

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humans are confirmed to be associated with their exposures. The low molecular weight

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hydroxylated metabolites of polycyclic aromatic hydrocarbons (OH-PAHs), which consist of

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2-3 benzene rings and part of 4 benzene rings, are excreted as metabolites of PAHs mainly

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into urine. Therefore, OH-PAHs contents in urine become biomarkers of human exposure

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quantity to PAHs.36 For example, human exposure to PAHs can occur through cigarette smoke.

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The concentration of urinary OH-PAHs from smokers were detected and the statistical data

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were 7325-10090 ng·L-1 for 2-hydroxynaphthalene, 871-1125 ng·L-1 for 2-hydroxyfluorene

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and 40-119 ng·L-1 for hydroxyphenanthrene, 1-hydroxypyrene.37 Up to now, a variety of 5



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analytical methods have been established for detecting urinary OH-PAHs, such as ultra-high

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performance liquid chromatography (UPLC),38 liquid chromatographic tandem mass

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spectrometry

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synchronous fluorescence spectroscopy,41 immunochemical assays42 and electrochemistry.43

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However, these analytical methods have limitations of low instrumental popularity,

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time-consuming derivatization steps or large disturbance from matrix. The determination of

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OH-PAHs in biological samples is a major challenge for their trace concentration level.

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Therefore, materials with excellent enrichment capacity are strongly expected for improving

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the sensitivity. Considering the abundant phenyl rings and the extensive conjugated structure

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throughout the whole network of the CMPs, CMPs might have an ideal enrichment capacity

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to OH-PAHs with benzene fused ring structure.

(LC-MS/MS),39

gas

chromatography-mass

spectrometry

(GC-MS),40

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In this study, we proposed a novel linkage strategy about the synthesis of CMPs with

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built-in magnetic nanoparticles for excellent enrichment of trace OH-PAHs in human urine.

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We modified Fe3O4 nanoparticles with boronic acid groups and then reacted with reactive

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monomers of polyphenylene conjugated microporous polymer (PP-CMP) by one-pot reaction

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to get magnetic PP-CMP with built-in Fe3O4 nanoparticles via chemical bonding assembly.

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The resultant magnetic PP-CMP was used for the enrichment of trace OH-PAHs in human

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urine samples of both smokers and non-smokers in combination with high-performance liquid

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chromatography with fluorescence detection (HPLC-FLD). The hydrophobicity, extensive

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conjugated system and suitable microporous structure of PP-CMP made it an outstanding

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material for the enrichment of OH-PAHs, which would play an important role to improve the

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sensitivity of trace analysis.

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EXPERIMENTAL SECTION

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Materials and Chemicals. Ferric chloride (FeCl36H2O) and ferrous chloride

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(FeCl24H2O) were of analytical grade and purchased from Shenyang Chemical Reagent

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Factory

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3-aminophenylboronic acid monohydrate (APB, 98%), 1,2,4,5-tetrabromobenzene (TBB,

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98%), 1,4-benzene diboronic acid (BDBA, 97%) and tetrakis(triphenylphosphine)palladium(0)

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[Pd(PPh3)4, 99.8%] were bought from J&K (Beijing, China). 1-Hydroxynaphthalene (1-NAP,

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99.0%), 2-NAP (99.0%) and 1-hydroxypyrene (1-PYR, 98%) were purchased from Aladdin

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Chemistry

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4-hydroxyphenanthrene (4-PHEN, 99%), 9-hydroxyphenanthrene (9-PHEN, 99%) were

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obtained from Toronto research chemicals inc (Canada). 6-Hydroxychrysene (6-CHRY,

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100.0%) was synthesized by Dr. Ehrenstorfer GmbH (Germany). 2-Hydroxyfluorene

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(2-FLUO, 98%) and β-glucuronidase/arylsulphatase from Helix pomatia were from Sigma

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(USA). Tetraorthosilicate (TEOS), ammonium bicarbonate, aqueous ammonia solution (30

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wt %), potassium carbonate (K2CO3), N, N′-dimethylformamide (DMF), sodium acetate

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(NaAc), ethylene glycol (EG) and acetic acid (HAc) of analytical grade were obtained from

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Guangzhou Chemical Reagent Factory (Guangzhou, China). Methanol of HPLC grade was

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bought from Dikma (Beijing, China). All of the other chemical reagents were of analytical

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grade. Stock solutions of OH-PAHs were prepared at 500 mg·L-1 and stored in refrigerator.

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The working solutions were prepared by applicable dilution with methanol to get an expected

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concentration just before use.

(Shenyang,

China).

(Shanghai,

3-Glycidyloxypropyltrimethoxysilane

China).

2-Hydroxyphenanthrene

(GLYMO,

(2-PHEN,

97%),

99%),

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Instrumentals. Transmission electron microscopic (TEM) images were recorded with a

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PHILIPS TECNAI 10 TEM instrument (Philips, Netherlands). Infrared absorption spectra 7



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were acquired by a NICOLET AVATAR 330 Fourier transform infrared (FT-IR) spectrometer.

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Fluorescence spectra were

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(SHIMADZU, Japan). Thermal stability evaluation was conducted on a thermogravimetric

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(TG) analyzer (Netzsch-209, Bavaria, Germany). Magnetic hysteresis curve was performed

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on a SQUID-based magnetometer form Quantum Design (San Diego, CA). Nitrogen sorption

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analysis was obtained on an ASAP-2020M gas adsorption instrument (Micromeritics, Atlanta,

168

USA).

obtained on a RF-5301PC fluorescence spectrometer

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Synthesis of Boronic-acid-functional Fe3O4 Nanoparticles. 10 nm Fe3O4 nanoparticles

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were prepared via the modified coprecipitation method.44 150 nm Fe3O4 nanoparticles were

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prepared via the modified solvothermal reduction method.45 The above two different-sized

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Fe3O4 nanoparticles were modified with TEOS, and then Fe3O4@SiO2 nanoparticles were

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obtained. The detailed synthetic method of Fe3O4@SiO2 nanoparticles can be seen in

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supporting information. Subsequently, we modified the Fe3O4@SiO2 nanoparticles with

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boronic-acid-functional groups by two-step post graft method to obtain Fe3O4@SiO2-APB.

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Firstly, GLYMO (1 mL) were dispersed in methylbenzene (60 mL) and 125 mg Fe3O4@SiO2

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nanoparticles were added to the above mixed solution. Secondly, the mixture was

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mechanically stirred at 80℃ for 12 h. Finally, to make sure to completely remove excess

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GLYMO, the Fe3O4@SiO2-GLYMO nanocomposites were washed with ethanol for three

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times. Subsequently, 50 mg APB was dissolved entirely in 60 mL of NH4HCO3 (50 mM, pH >

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8) under ultrasonic processing. After that, Fe3O4@SiO2-GLYMO (50 mg) and the above

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mentioned APB solution (20 mL) were mixed together under rapid stirring at 65℃ for 3 h,

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and then, the supernatant was removed by magnetic separation. APB solution (20 mL) was

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added again, and the process was repeated for 3 times to obtain Fe3O4@SiO2-APB. 8


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Fe3O4@SiO2-APB nanocomposites were washed with ethanol five times and dried in vacuum

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oven at 150℃.

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Synthesis of Magnetic PP-CMP. We added Fe3O4@SiO2-APB as one of the functional

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components into the Suzuki crossing coupling reaction system from the very beginning to

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prepare magnetic PP-CMP. A mixture of TBB (100 mg, 0.254 mmol), BDBA (84 mg, 0.508

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mmol) and Fe3O4@SiO2-APB (100 mg) in DMF (24 mL) was degassed by three

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freeze-pump-thaw cycles. And then, an aqueous solution of K2CO3 (1.0 mol·L-1, 2 mL) and

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Pd(PPh3)4 (24.0 mg，20.8 µmol) were added to the mixture. Following by degasification with

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three freeze-pump-thaw cycles again, the mixture was purged with nitrogen, and mechanically

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stirred at 90℃ for 20 h. The precipitated product was separated by magnetic adsorption,

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completely

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dichloromethane, and rigorously washed by Soxhlet extractions with water, methanol and

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THF, respectively, to get magnetic PP-CMP.

washed

with

water,

methanol,

acetone,

tetrahydrofuran

(THF)

and

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Enrichment Procedure. For extraction of OH-PAHs, 10 mg of magnetic PP-CMP was

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added to 40 mL of standard solution or sample dissolved in water. The solution was first

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immersed into an ultrasonic bath for 30 s and then shaken on a rotator for a certain period.

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The magnetic PP-CMP was then collected by applying a magnet to the outer wall of the vial

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and shaken on a rotator with 400 µL of eluent for a certain period. The supernatant was

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collected and followed by HPLC analysis. HPLC conditions can be seen in supporting

204

information.

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Sample Pretreatment. Urine samples (36 mL) were first spiked with a mixture of

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sodium acetate buffer (0.1 mol·L-1, pH 5.5, 4 mL), and β-glucuronidase/arylsulfatase enzyme

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(120 µL), then hydrolyzed overnight by incubating at 37℃. 9



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RESULTS AND DISCUSSION

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PP-CMP with Built-in Fe3O4 Nanoparticles via Chemical Bonding Assembly. In

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order to synthesize PP-CMP with built-in Fe3O4 nanoparticles via chemical bonding assembly,

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we designed an inter-linkage strategy (Figure 1) between Fe3O4 nanoparticles and PP-CMP

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network. Firstly, we modified Fe3O4 nanoparticles with boronic-acid groups by three modified

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steps. Secondly, boronic-acid-functionalized Fe3O4 nanoparticles would together react with

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reactive monomers of PP-CMP to get magnetic PP-CMP. In typical experiments, 10 nm Fe3O4

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nanoparticles were synthesized by coprecipitation method and 150 nm Fe3O4 nanoparticles

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were

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tetraorthosilicate, the resulting magnetic nanoparticles were surface hydroxylated.

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3-Glycidyloxypropyltrimethoxysilane was easily chemically coupled with those hydroxyl

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groups to get glycidyl modified Fe3O4 nanoparticles, which could react with amino groups of

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boronic-acid-functionalized reagent APB. Up to now, we got the boronic-acid-functionalized

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Fe3O4

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Fe3O4@SiO2-APB-150 respectively in the case of Fe3O4 nanoparticles are 10 nm or 150 nm,

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respectively). Both Fe3O4@SiO2-APB and one of the reactive monomers 1,4-benzene

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diboronic acid have the same high reactive activity, which together reacted with another

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reactive monomers 1,2,4,5-tetrabromobenzene. Through this one-pot Suzuki coupling

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reaction, we got the magnetic PP-CMP (magnetic PP-CMP-10 and magnetic PP-CMP-150

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respectively). Obviously, we could get many advantages from this idea for design of modified

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Fe3O4 nanoparticles. First, PP-CMP network was developed and Fe3O4 nanoparticles were

229

simultaneously built in the network via chemical bonding assembly. Second, we could get

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magnetic PP-CMP products rapidly by one-pot method. Third, the similar reaction-activity of

synthesized

by

nanoparticles

solvothermal

called

reduction

method.

Fe3O4@SiO2-APB

Through

hydrolyzation

(Fe3O4@SiO2-APB-10

10


of

and

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reactive monomers 1,4-benzene diboronic acid and modified Fe3O4 nanoparticles could result

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in a stable and homogenous magnetic CMP framework.

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Characterization of the Magnetic PP-CMP. In order to clarify the morphological

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image, TEM was used to characterize the as-synthesized magnetic PP-CMP nanoparticles. As

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shown in the TEM image (Figure 2), the modified 10-nm-Fe3O4 nanoparticles were built in

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PP-CMP network to form magnetic PP-CMP-10 while the modified 150-nm-Fe3O4

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nanoparticle acted as a core in the PP-CMP shell to form core-shell magnetic PP-CMP-150.

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For the magnetic PP-CMP-10, numerous nanoparticles dispersed throughout the PP-CMP to

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form a microsphere with the diameter about 800 nm. In the case of the magnetic PP-CMP-150,

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we can see a layer of irregular curls, which were in the same shape as the bare PP-CMP

241

reported by Jiang,46 were wrapped around the smooth-edge core Fe3O4@SiO2-APB-150.

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Compared with magnetic PP-CMP-10, core-shell magnetic PP-CMP-150 would have a

243

smaller proportion of PP-CMP because of its comparatively larger Fe3O4 core and thinner

244

PP-CMP shell. Considering the adsorption sites were provided by PP-CMP networks,

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magnetic PP-CMP-10 was supposed to be a better adsorbent material with higher proportion

246

of PP-CMP, and was chosen for the following studies.

247

FTIR spectrum was shown in Figure S1. Compared with the FTIR spectrum of

248

Fe3O4@SiO2-APB (curve a), the magnetic PP-CMP composites (curve b) added new signals

249

of 1470, 1004, 832 and 697 cm-1, which were assigned to C=C vibrational modes of the

250

substituted phenyl rings, C-Br stretch, C-H out-of-plane bending modes from the

251

di-substituted phenyl rings and C-H out-of-plane bending modes from the tetra-substituted

252

phenyl rings, respectively. These new peaks were perfectly consistent with the signals of bare

253

PP-CMP in our laboratory (curve c) and reported by Jiang,46 indicating that the composites 11



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254

formed by Fe3O4@SiO2-APB and PP-CMP have been successfully synthesized. As for

255

fluorescence spectra (Figure S2) of magnetic PP-CMP composites dispersed in THF at 25℃,

256

the excitation and emission maximum wavelengths of magnetic PP-CMP-10 were 307 nm and

257

422 nm, respectively. Jiang24 reported that bare PP-CMP showed an emission maximum at

258

435 nm on excitation at 312 nm under the same experience condition. Under the influence of

259

composite effect, the emission band of magnetic PP-CMP composites shifted to shorter

260

wavelengths but was still basically coincident to that of bare PP-CMP, while there were not

261

any luminescence emitting by Fe3O4@SiO2-APB, demonstrated that the synthesis of magnetic

262

PP-CMP composites was achieved. TGA measurement was performed to determine the

263

thermostability of magnetic PP-CMP. As we can see in Figure S3, magnetic PP-CMP would

264

not decompose before 285℃.

265

The magnetization curve of the magnetic PP-CMP displayed superparamagnetic

266

properties. As shown in Figure 3, magnetic PP-CMP-10 possessed a typical magnetic

267

hysteresis curve. In comparison with 72.8 emu·g-1 for pure Fe3O4 nanoparticles,47 magnetic

268

PP-CMP-10 exhibited a high saturation magnetization of 33.6 emu·g-1. A magnified section of

269

the magnetization curve near the zero magnetic field was shown in the inset of Figure 3.

270

Saturation remanence (Mrs) was 2.0 emu·g-1 and coercivity (hc) was 39.5 Oe, respectively,

271

which meant that a quite low residual magnetization would be present on removal of the

272

external magnetic field and reducing the magnetization to zero just needed a low intensity of

273

applied magnetic field. These characteristics demonstrated that the built-in Fe3O4

274

nanoparticles are superparamagnetic, which made the magnetization of magnetic PP-CMP by

275

an external magnetic field be easily realized.

276

The gas sorption isotherms were obtained by nitrogen sorption analysis. As shown in 12


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277

Figure 4, magnetic PP-CMP-10 with built-in Fe3O4 nanoparticles displayed typeⅠgas

278

sorption isotherms, which was suggestive of a microporous structure. The total pore volume

279

was 0.260 cm3·g-1 . The BET surface area and the Langmuir surface area are 194.8 m2·g-1 and

280

254.1 m2·g-1, respectively. For the magnetic PP-CMP-10, the surface areas are decreased to

281

some extent because of the doping of Fe3O4 nanoparticles. The pore width of magnetic

282

PP-CMP was calculated by the nonlocal density functional theory (NLDFT) method. As

283

shown in Figure S4, pore size distributions of magnetic PP-CMP-10 consisted of two parts.

284

The major part was at about 1.3 nm which was from the micropore structure of CMP network.

285

Since the embedding of Fe3O4 nanoparticles into PP-CMP network, the minor part at larger

286

pore size generated.

287

Adsorption Characteristics of the Magnetic PP-CMP. The study about the adsorption

288

characteristics of the magnetic PP-CMP for organic analytes is crucial to explore their

289

potential applications. Considering the abundant phenyl rings throughout the whole network

290

of the magnetic PP-CMP, OH-PAHs were selected to represent the adsorption characteristics

291

of the materials. Their adsorption affinity on the magnetic PP-CMP was evaluated (Table 1)

292

and the adsorption amount curves were shown in Figure S5. In order to identify the

293

adsorption mechanism of OH-PAHs on magnetic PP-CMP, the adsorption isotherm data of six

294

OH-PAHs with typical structure were fitted with the most conventional models: Henry

295

(equation 1), Langmuir (equation 2) and Freundlich (equation 3).

296

qe = KdCe

(1)

297

qe = qmaxKLCe/(1+KLCe)

(2)

298

qe = KFCen

(3)

299

where: qe is the adsorption capacity of magnetic PP-CMP at equilibrium (µg·mg-1); Ce is the 13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

300

concentration of OH-PAHs in the equilibrium solution (mg·L-1); Kd, KL, and KF are the

301

constants for Henry (L·g-1), Langmuir (L·mg-1) and Freundlich (µg·mg-1)(mg·L-1)-n,

302

respectively; n is the heterogeneity factor (-); and qmax is the maximum amount of adsorbate

303

(µg·mg-1).

304

As shown in Table S1, when the adsorption isotherm data of 2-PHEN, 4-PHEN and

305

1-PYR were fitted with Langmuir equation, qmax came to be negative numbers, which was

306

obviously at variance with objective reality. Compared with Freundlich equation, the related

307

coefficient R2 of Henry equation (range from 0.9484 to 0.9952, Figure S6) was higher,

308

indicated that Henry equation was the best model in those three to describe the adsorption

309

behaviors of OH-PAHs on the magnetic PP-CMP. The parameter Kd in Henry equation can

310

commendably describe the organic distribution process in solid-liquid system.48 We made a

311

linear fitting between Kd and KOW of those 6 OH-PAHs, and the linear related coefficient R2

312

was up to 0.9800 (Figure 5). This significant linear positive correlation between Kd and KOW

313

indicated that hydrophobic interaction contributes the main interaction between OH-PAHs and

314

magnetic PP-CMP. Besides, it was an extremely large conjugated system in magnetic

315

PP-CMP that was abundant of delocalized π electrons of the aromatic ring. Considering the

316

polycyclic aromatic structure of OH-PAHs, π-π stacking interaction played an important role

317

in adsorption, which could be further demonstrated by the adsorption amounts of OH-PAHs

318

increased with an increase of the condensed ring. Last but not the least, highly porous

319

structure of the CMPs with appropriate pore structure and suitable pore size must be involved.

320

Micropores from CMP network were good at adsorbing smaller size OH-PAHs with 2-3

321

aromatic rings, while the larger pores, formed by encapsulating Fe3O4 nanoparticles, were

322

beneficial complement for adsorbing larger size OH-PAHs with 4 aromatic rings. Judging 14


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323

from these adsorption characteristics of the magnetic PP-CMP, it has a potential for extraction

324

of other analytes with aromatic structure, for example, polychlorinated biphenyls and

325

aromatic amines.

326

Application to Analysis of Trace OH-PAHs in Human Urine. A new analytical

327

method coupling the magnetic PP-CMP with HPLC was developed for the determination of

328

OH-PAHs in human urine. As shown in Figure S7, significant conditions including

329

desorption solvent, adsorption time and desorption time were optimized. The chosen

330

desorption solvent was acetone and the corresponding extraction time and desorption time

331

were 60 and 15 min, respectively. As summarized in Table 2, this method displayed favorable

332

linearity in the range of 0.03-300 µg·L-1 for OH-PAHs. Their correlation coefficients (R2)

333

ranged from 0.9937 to 0.9999. The detection limits of the OH-PAHs ranged from 0.01 µg·L-1

334

to 0.08 µg·L-1 based on a signal-to-noise ratio of 3 (S/N = 3). The RSDs (n = 5) of magnetic

335

PP-CMP materials from one batch ranged from 3.5% to 7.5% and the RSDs (n = 3) of

336

batch-to-batch ranged from 8.4% to 10.5%, which were calculated at OH-PAHs concentration

337

of 1.00-7.50 µg·L-1. After replicate extraction for 200 times, the adsorption property of

338

magnetic PP-CMP materials had no significantly difference. Compared with some other

339

pretreatment methods coupled with HPLC-FLD for detection of OH-PAHs in human urine,

340

this method was more sensitive than or comparable with the reported method for detection of

341

OH-PAHs.49-51 In addition, magnetic separation made the operation easy and convenient. The

342

superparamagnetism and the large proportion of Fe3O4 nanoparticles in magnetic PP-CMP

343

made the separation process become very fast (＜20 s). The results proved that the novel

344

magnetic PP-CMP was stable and durable, and the method was reliable and sensitive for

345

simultaneous determination of the trace OH-PAHs. 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

346

To further illustrate the stability of the magnetic PP-CMP, it was soaked in various

347

solvents for 7 days, including acid, alkali, water, THF, DMSO and other organic solvents. The

348

adsorption amounts for OH-PAHs were still consistent with those have not been treated in any

349

solvents (Figure S8). The RSDs of adsorption amounts for OH-PAHs on magnetic PP-CMP

350

after being soaked in ten different kinds of solvents ranged from 1.9%-3.2%. It was firmly

351

conjugated structure of PP-CMP with chemical bonding linkage, together with chemical

352

bonding between Fe3O4 nanoparticles and PP-CMP, that made the magnetic PP-CMP

353

materials stable enough in harsh condition. With this advantage of highly chemical stability,

354

there would be fewer limitations in practical application of magnetic PP-CMP.

355

The proposed method was used for the analysis of trace OH-PAHs in human urine.

356

Typical chromatograms of trace OH-PAHs from human urine were shown in Figure 6, and

357

the quantification results were summarized in Table 3. It was favorable that most of the target

358

OH-PAHs could be detected from human urine by this new method and quantified to be in the

359

range of 0.054-0.802 µg·L-1 and 0.047-5.962 µg·L-1 from non-smoker and smoker,

360

respectively. Obviously, smoker’s urine samples had a higher amount of OH-PAHs because of

361

inhaling PAHs from cigarettes. Compared with smoker 1, smoker 2 who smoked fewer

362

cigarettes a day had a lower amount of OH-PAHs in his urine samples. To some extent, it

363

indicated that OH-PAHs from human urine would be increased with the increasing of daily

364

smoking amount. Method validation was conducted by the spiked experiment. The recoveries

365

of human urine samples were 76.0%-107.8% and the RSDs were 1.9%-8.1%. The results

366

demonstrated that this new method was sensitive, practical and reliable for the simultaneous

367

analysis of trace OH-PAHs from real samples, and had potential for the response of daily

368

smoking amount. 16


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369


CONCLUSIONS

370

We have reported that a modified Fe3O4 nanoparticles linkage strategy for synthesis of

371

PP-CMP with built-in Fe3O4 nanoparticles via chemical bonding assembly. The magnetic

372

PP-CMP materials have a high saturation magnetization and show rapid magnetic response.

373

The resultant magnetic PP-CMP provided the significant enrichment superiority for OH-PAHs.

374

We suggest that the driving force for adsorption is mainly dictated by hydrophobic interaction,

375

with the assistance of π-π stacking interaction, highly porous structure, appropriate pore

376

structure and suitable pore size. The magnetic PP-CMP was successfully applied for the

377

enrichment and analysis of trace OH-PAHs in human urine samples. It is expected that CMPs

378

are a species of materials with great promise for sampling, enrichment, and separation. The

379

results of our research indicate that the prospect of CMPs for wide application in analytical

380

chemistry, and modified Fe3O4 nanoparticles linkage strategy for synthesis of magnetic

381

PP-CMP can be extended to most of the chemical bonding assembly between dopants and

382

polymer networks.

383 384

ACKNOWLEDGEMENTS

385

The work were supported by the National Natural Science Foundation of China

386

(Nos.21575168, 21277176 and 21475153), the Guangdong Provincial Natural Science

387

Foundation of China (No. 2015A030311020), and the Special funds for public welfare

388

research and capacity building in Guangdong Province of China (No. 2015A030401036),

389

respectively.

390 391 392 393 17



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394 395

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482


FIGURES

483

484 485

Figure 1. Illustration of synthesis of magnetic PP-CMP by the Suzuki coupling of phenylboronic

486

acid-modified Fe3O4 nanoparticles, 1,2,4,5-tetrabromobenzene, and 1,4-benzene diboronic acid.

487 488 489 490 491 492 493 494 495 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

496

497 498

Figure 2. TEM image of (A) Fe3O4@SiO2-APB-10, (B) magnetic PP-CMP-10, (C) Fe3O4@SiO2-APB-150

499

and (D) magnetic PP-CMP-150.

500 501 502 503 504 505 506 22


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507

508 509

Figure 3. Magnetic hysteresis curve of magnetic PP-CMP-10. The inset shows the same curve when the

510

external magnetic field is near zero, where in the two markers present the values of saturation remanence

511

(Mrs = 2.0 emu·g-1) and coercivity (hc = 39.5 Oe), respectively.

512 513 514 515 516 517 518 519 520 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

521

522 523

Figure 4. N2 adsorption isotherms of magnetic PP-CMP-10.

524 525 526 527 528 529 530 531 532 533 534 535 24


Page 24 of 30

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536

537 538

Figure 5. Linear fitting between Kd and KOW. Linear related coefficient R2 was up to 0.9800.

539 540 541 542 543 544 545 546 547 548 549 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

550 551

552 553

Figure 6. Chromatograms for the analysis of the standard solution and human urine sample. (a) Smoker 1’s

554

urine sample with the enrichment by magnetic PP-CMP; (b) Smoker 2’s urine sample with the enrichment

555

by magnetic PP-CMP; (c) Non-Smoker’s urine sample with the enrichment by magnetic PP-CMP; (d)

556

Direct injection of non-smoker’s urine sample; (e) Mixed standard of 1 µg·L-1 OH-PAHs with the

557

enrichment by magnetic PP-CMP. Peak identity: 1, 2-NAP; 2, 2-FLUO; 3, 2-PHEN; 4, 9-PHEN; 5,

558

4-PHEN; 6, 1-PYR; 7, 6-CHRY.

559 560 561 562 563 564 565 26


Page 26 of 30

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566


TABLES

567 Table 1. Adsorption of OH-PAHs on the magnetic PP-CMP

568

Adsorption amount Compounds

Structural formula

Molecular weight

Log KOW a (nmol·mg-1)

569

a

2-NAP

144

2.69

153

1- NAP

144

2.69

162

2-FLUO

182

3.54

269

2-PHEN

194

3.86

278

9-PHEN

194

3.86

318

4-PHEN

194

3.86

313

1-PYR

218

4.45

322

6-CHRY

244

-

305

KOW: n-octanol/water partition coefficients. Data taken from Ohura.52

570 571 572 573 574 575 576 577 578 27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 30

579 580

Table 2. Linear range, detection limit, and precision of magnetic PP-CMP enrichment based HPLC method

581

for the determination of OH-PAHs RSDa Correlation Compounds

Linear range (µg·L-1)

LOD (µg·L-1)

One batch

Batch-to-batch

(%,n=5)

(%,n=3)

2

coefficient R

2-NAP

0.26-120

0.9981

0.08

4.2

9.5

2-FLUO

0.13-16

0.9937

0.04

7.5

9.3

2-PHEN

0.19-85

0.9994

0.06

3.5

10.5

9-PHEN

0.16-300

0.9981

0.05

4.1

8.4

4-PHEN

0.03-88

0.9999

0.01

6.1

10.2

1-PYR

0.05-150

0.9998

0.02

4.5

8.7

6-CHRY

0.03-28

0.9986

0.01

4.2

9.5

582

a

RSD: Calculated at concentration of 5.00, 1.00, 2.50, 7.50, 3.00, 3.00 and 2.00 µg·L-1 respectively for 2-NAP, 2-FLUO,

583

2-PHEN, 9-PHEN, 4-PHEN, 1-PYR and 6-CHRY, respectively.

584 585 586

28


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587 588

Table 3. Original amounts and recoveries of OH-PAHs for human urine samples (n =3) Smoker 1b

Non-smoker Original Compounds

Original Added

Recovery

RSD

amount (µg·L-1)

(%)

Recovery

RSD

Added

Recovery

RSD

(µg·L-1)

(%)

(%,n=3)

amount (µg·L-1)

(%,n=3)

(%)

(%,n=3)

-1

(µg·L )

a

Original Added

amount

-1

589

Smoker 2c

-1

(µg·L )

(µg·L )

2-NAP

0.802

0.500

100.9

5.6

5.962

6.000

101.5

4.5

4.683

4.500

103.9

2.7

2-FLUO

0.141

0.200

105.8

4.8

0.673

0.750

103.1

5.0

0.297

0.300

106.3

4.1

2-PHEN

0.248

0.400

76.0

8.1

0.457

0.500

85.2

3.6

0.253

0.250

79.1

4.7

9-PHEN

0.207

0.375

98.2

2.7

0.239

0.250

95.5

3.7

0.214

0.200

95.3

3.5

4-PHEN

0.054

0.050

106.5

4.7

0.110

0.100

104.3

2.8

0.085

0.100

106.7

2.3

1-PYR

0.082

0.150

107.8

1.9

0.170

0.200

99.4

2.4

0.139

0.150

105.3

2.5

6-CHRY

N.D.a

0.100

80.4

3.3

0.047

0.050

83.5

4.9

N.D.a

0.100

80.7

4.2

N.D., not detected. b Smoker 1 smoked 20 cigarettes a day. c Smoker 2 smoked 5 cigarettes a day.

590 591 592

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

593 594 595

Table of contents (TOC) image

596

597

30


Page 30 of 30

Conjugated Microporous Polymers with Built-In Magnetic

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