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Phosphorous-enriched knitting aryl network polymer for the rapid and effective adsorption of aromatic compounds
Accepted Manuscript Title: Phosphorous-enriched knitting aryl network polymer for the rapid and effective adsorption of aromatic compounds Authors: Qianqian Wang, Lihong Zhang, Lin Hao, Chun Wang, Qiuhua Wu, Zhi Wang PII: DOI: Reference:
S0021-9673(18)31177-4 https://doi.org/10.1016/j.chroma.2018.09.026 CHROMA 359691
To appear in:
Journal of Chromatography A
Received date: Revised date: Accepted date:
14-6-2018 8-9-2018 15-9-2018
Please cite this article as: Wang Q, Zhang L, Hao L, Wang C, Wu Q, Wang Z, Phosphorous-enriched knitting aryl network polymer for the rapid and effective adsorption of aromatic compounds, Journal of Chromatography A (2018), https://doi.org/10.1016/j.chroma.2018.09.026 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Phosphorous-enriched knitting aryl network polymer for the rapid and effective adsorption of aromatic compounds
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College of Science, Hebei Agricultural University, Baoding 071001, China
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Qianqian Wang, Lihong Zhang, Lin Hao, Chun Wang, Qiuhua Wu*, Zhi Wang*
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Correspondence: Professor Qiuhua Wu, College of Science, Hebei Agricultural University, Baoding 071001, Hebei, China; Tel: +86-312-7528291; Fax: +86-312-7528292; E-mail: [email protected]. Correspondence: Professor Zhi Wang, College of Science, Hebei Agricultural University, Baoding 071001, Hebei, China; Tel: +86-312-7521513; Fax: +86-312-7521513; E-mail: [email protected].
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Highlights
A phosphorous-enriched knitting aryl network (Ph-PPh3-KAP) was prepared.
The Ph-PPh3-KAP showed excellent adsorption ability to aromatic compounds.
A sensitive method was developed for analyzing phenylurea pesticides in real
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samples.
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The Ph-PPh3-KAP can serve as a promising adsorbent for other applications.
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ABSTRACT A phosphorous-enriched knitting aryl network polymer (named as Ph-PPh3-KAP) was fabricated by one-step crosslinking between triphenylphosphine and benzene, with formaldehyde dimethyl acetal as an external crosslinker. The Ph-PPh3-KAP had a large surface area and good
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physicochemical stability. Its adsorption performance for aromatic organic compounds was evaluated by using some dyes and benzene ring-containing compounds as the model adsorbates. The results exhibited that it had a rapid and effective adsorption for the aromatic organic
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compounds due to the hydrogen bonding and polar interactions of the Ph-PPh3-KAP with the target compounds. Then, the Ph-PPh3-KAP was explored as the adsorbent for the solid phase extraction of some phenylurea pesticides from lake water, tomato and cucumber samples prior to HPLC analysis. Under optimal conditions, the linear responses of the phenylurea pesticides were 0.1-100 ng mL-1
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for lake water and 0.5-100 ng g-1 for cucumber and tomato samples. The limits of detection for the
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analytes at S/N = 3 were 0.01-0.02 ng mL-1 for lake water and 0.03-0.05 ng g-1 for cucumber and
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tomato samples. The recoveries were in the range from 80.8% to 118%. The Ph-PPh3-KAP
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exhibited a great application potential for extraction of aromatic compounds.
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Keywords: Knitting aryl network polymer, Solid phase extraction adsorbent, Phenylurea pesticides
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1 Introduction The porous organic framework (POF) materials, with their large surface area and high physicochemical stability, have attracted enormous scientific attention because of their diverse application potentials in gas storage and separation [1, 2], heterogeneous catalysis [3], sensor [4-6] and removal of heavy metal ions [7]. Over the last few decades, the research in developing so useful
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POFs has resulted in a lot of novel organic porous materials including hyper-crosslinked polymers (HCPs) [8], polymer of intrinsic microporosity (PIMs) [9], conjugated microporous polymers (CMPs) [10] and covalent organic frameworks (COFs) [11]. Among them, HCPs have recently
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undergone a rapid development as a promising class of microporous materials and become widely focused materials because of their low cost, simple and versatile synthesis. HCPs are primarily synthesized by three methods: (1) post-crosslinking polymer precursors [12], (2) direct one-step polycondensation of functional monomers [13], and (3) knitting rigid aromatic building blocks with
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external crosslinkers to obtain knitting aromatic polymers (KAPs) [14]. Compared with the first two
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methods, the knitting strategy which was first developed by Tan and co-workers in 2011 for the
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preparation of KAPs is a breakthrough [14], in which formaldehyde dimethyl acetal (FDA) was used as a crosslinker to link simple aromatic compounds like benzene or biphenyl with rigid
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methylene bridges through the Friedel-Crafts reaction catalyzed by anhydrous FeCl3. The knitting strategy allows the use of a wide variety of aromatic building blocks containing different functional
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groups such as methylbenzene, chlorobenzene and phenols [15, 16], and it also allows the use of heterocyclic aromatic building blocks such as furan, thiophene and pyrrole [17], thereby increasing
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the diversity and the functionality of the KAPs. Moreover, by changing the molar ratio of crosslinkers to monomers, the inner skeleton of the KAPs can be easily adjusted [13, 18], thus
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resulting in an abundant porous structure and high surface area. Since the knitting strategy has such outstanding characteristics, it has been developed rapidly and has become a platform to prepare new porous materials with diverse structure, composition and functionality [19, 20]. As a new class of organic porous material, KAPs have caught a lot of research attention, and
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some of them have been successfully applied in gas storage [21, 22], heterogeneous catalysis [23, 24], and separation and purification [25, 26]. The KAP with benzene as the monomer and FDA as the crosslinker has been used as stationary phase for capillary gas chromatography [27] and electrochromatography [28], displaying a potential applicability of KAPs in the adsorption and separation field. Since KAPs possess extended π-electron system and highly stable conjugated structure, they are expected to have a strong adsorption affinity toward aromatic compounds by 3
π-stacking effect, making them possible to be superior adsorbents for aromatic organic compounds. Nevertheless, so far, the applications of KAPs as adsorbent still remain rarely exploited [16]. Very recently, a novel functionalized KAP (Ph-PPh3) was prepared by knitting triphenylphosphine (PPh3) with benzene [24, 29] for the use as catalyst support. Since the KAP Ph-PPh3 contains large π-electron conjugated system and many P atoms, it should have the capability to effectively adsorb some compounds by π-π stacking and polar interactions. However, so far there have been no reports for its applications in analytical chemistry.
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In this work, the Ph-PPh3-KAP was prepared by using PPh3 and benzene as building blocks and FDA as an external crosslinker [24]. To explore its adsorption capability, the Ph-PPh3-KAP
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was investigated as the adsorbent for the first time with some aromatic organic compounds including some dyes (acid fuchsin, acid orange 74, congo red and malachite green), phenylurea herbicides (PUHs), benzoylurea insecticides, phthalate esters, carbamate insecticides and chlorophenols as model adsorbates. The Ph-PPh3-KAP showed rapid adsorption kinetics and large
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Ph-PPh3-KAP
as
the
adsorbent
coupled
with
high
performance
liquid
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with
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adsorption ability toward the aromatic compounds. Finally, a solid-phase extraction (SPE) method
chromatography-ultraviolet detection (HPLC-UV) was established for the determination of five
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PUHs (metoxuron, monuron, chlortoluron, monolinuron and buturon) in lake water, cucumber and
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tomato samples.
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2 Experimental
The description about the reagents and apparatus is provided in the Electronic Supporting
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Material (ESM).
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2.1 Synthesis of Ph-PPh3-KAP
Ph-PPh3-KAP was prepared according to the method reported in the previous literature [24].
Briefly, 9.75 g anhydrous ferric chloride and 1.56 g benzene were added to 20 mL dichloroethane solution containing 5.25 g triphenylphosphine and 4.56 g FDA. After the mixture was heated at 45 o
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C for 5 h under magnetic stirring to form a primary network, the reaction temperature was raised
to 80 oC for 12 h to finish the cross-linking procedure (a condenser was used for reflux). After cooling, the resulting solid product was obtained by filtration and then thoroughly washed with methanol until the filtrate turned clear. After the solid product was further purified by Soxhlet extraction with methanol for 24 h and vacuum dried at 60 oC for 24 h, the final Ph-PPh3-KAP was obtained. The scheme for the synthesis of the Ph-PPh3-KAP is shown in Figure 1. 4
2.2 Adsorption kinetics The adsorption kinetic studies were performed as follows: 30 mg of the Ph-PPh3-KAP was put into 50 mL dye solution with its initial concentration at 50 mg L-1. Then, the mixture was shaken on a slow-moving platform shaker. At the interval of an appropriate time, the Ph-PPh3-KAP adsorbent was removed from the solution by filtration, and the residual dye concentration in the filtrate was
by the Ph-PPh3-KAP was calculated according to the following equations: C0 Ct V m
qe
C0 C e V m
(1)
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qt
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determined with a UV-visible spectrophotometer at 478 nm (λmax). The removed quantity of the dye
(2)
where qt (mg g-1) and qe (mg g-1) represent the removed quantity of the dye by the Ph-PPh3-KAP at
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any time t (min) and at equilibrium, respectively; C0, Ct and Ce (mg L-1) stand for the dye
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concentration at the initial, at any time t and at equilibrium, respectively; V (L) is the volume of the
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solution; m (g) is the mass of the Ph-PPh3-KAP.
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2.3 Sample preparation
The tomato or cucumber sample was homogenized by a laboratory homogenizer. Then 50.0 g
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of the homogenized sample was weighed and put into two 50.0-mL plastic centrifugation tubes. After the centrifugation at 5000 rpm for 10 min, the supernatant was transferred into a conical flask.
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Then, the sediment was extracted with 5.0 mL acetonitrile by vortexing it for 3 min and then centrifuged. After all of the supernatants were filtered and transferred to a 100.0-mL volumetric
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flask, the volume was made to the mark with distilled water. Then, the resulting sample solution was used for the subsequent SPE. The lake water was first filtered with 0.45 μm membrane and then used for the following SPE.
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2.4 SPE procedures
15 mg of the Ph-PPh3-KAP was packed in a 3 mL empty SPE cartridge, and then the packed cartridge was conditioned with 6 mL methanol and 6 mL distilled water. Then, 100 mL sample solution was loaded into the cartridge at a flow rate of 10 mL min-1. After the cartridge was washed with 5 mL of acetonitrile-water mixture (10:90, V / V), the SPE cartridge was vacuum dried. Then, 5
the analytes were eluted with 1 mL acetonitrile at the elution rate of 0.5 mL min-1. After being filtered with 0.22 μm membrane, 20 μL of the eluate was analyzed by the HPLC. Before the next extraction, the cartridge was washed successively with 0.3 mL acetonitrile and 2 mL distilled water to ensure that there was no carry-over in the cartridge. 3 Results and discussion
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3.1 Characterization of the Ph-PPh3-KAP Ph-PPh3-KAP was first subjected to FT-IR characterization. Figure 2(a) shows that a series of characteristic bands at 1437, 1600-1450, 1250-950, and 900-650 cm-1 exist, which are consistent
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with the literature report [30], confirming the successful synthesis of the Ph-PPh3-KAP. The peak at 1437 cm-1 corresponds to the vibrations of P-CH2 bond, indicating that the phosphine ligand is embedded in the backbone of the Ph-PPh3-KAP [31]. The peaks at 1600-1450 cm-1 can be attributed
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to the benzene skeleton stretching, and the peaks in the vicinity of 1250-950 cm-1 and 900-650 cm-1 result from the C-H out-of-plane bending and in-plane bending vibrations of the benzene ring,
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respectively [32]. The peak at 3500 cm-1 can be assigned to the O-H stretching vibration coming
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from the water molecules adsorbed by the Ph-PPh3-KAP [16, 33]. In addition, the C-H stretching
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vibration of the methylene bridge bonds can be found from the double peaks at nearly 2900 and 2850 cm-1 [33].
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The nitrogen adsorption-desorption isotherms were measured to investigate the porosity and surface area of the Ph-PPh3-KAP. The surface area of the Ph-PPh3-KAP was measured to be 659 m2 g-1. The adsorption isotherm and pore size distribution of the Ph-PPh3-KAP are shown in Figure
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2(b). A rapid uptake at low relative pressures of 0-0.03 indicates a rich microporous structure, a slight hysteresis loop suggests the existence of some mesopores, and a sharp rise in the relative
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pressures from 0.8 to 1.0 reflects the presence of macropores in the Ph-PPh3-KAP. The Barrett-Joyner-Halenda (BJH) adsorption average pore width was 6.12 nm, and the total pore volume was 0.57 cm3 g-1. The isotherm curves of sorption and desorption were not closed due to the
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pore structure deformation resulting from some degree of the polymer network swelling in liquid nitrogen [34]. The morphology and porous structures of the Ph-PPh3-KAP were observed by both SEM and TEM. Figure 2 (c) and Figure S1 exhibit that the Ph-PPh3-KAP had an amorphous morphology with a porous nature. In addition, the size of Ph-PPh3-KAP particles was measured and Figure S2 shows that the size of Ph-PPh3-KAP was mainly distributed in the range of 0.71-1.99 μm and the average particle size was about 1.35 μm. 6
To examine the thermal stability of the Ph-PPh3-KAP, TGA was performed by heating the Ph-PPh3-KAP from room temperature to 800 oC at a ramping rate of 10 oC min-1 under nitrogen flow. The TG curve in Figure 2(d) shows that the Ph-PPh3-KAP was stable up to 350 °C, displaying an excellent thermal stability [35, 36]. 3.2 Adsorption performance To investigate the adsorption ability of the Ph-PPh3-KAP, the adsorption experiments for
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different dyes were conducted by adding 10 mg of the Ph-PPh3-KAP in 10 mL each of 20 mg L-1 different dyes solutions respectively, including acid fuchsin, acid orange 74, congo red and
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malachite green. As shown in Figure 3, the Ph-PPh3-KAP particles were uniformly dispersed in the dye solutions. The color of the dye solutions became obviously lighter after the mixture was shaken for 5 minutes. In order to clearly observe the adsorption effect, the above dye solutions were filtered and the filtrates were compared with the untreated ones. Obviously, all of the filtrates of the four
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dyes after treatment are clear and colorless, indicating that the Ph-PPh3-KAP can rapidly remove
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the dyes in a short time. Thus, it is expected that the Ph-PPh3-KAP can serve as an adsorbent to
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adsorb some organic compounds.
In order to evaluate the adsorption kinetics of the Ph-PPh3-KAP, the adsorption experiments
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were carried out by using acid orange 74 as a model adsorbate. A pseudo-second-order kinetic
t 1 t 2 qt kqe qe
(3)
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model was used to study the adsorption kinetics, and it is expressed as follows:
Where qe and qt are the amounts of the adsorbed analytes at equilibrium and at any time t,
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respectively, k is the rate constant. The values of k and qe can be obtained from the slope and interception of the linear regression of t/qt versus t (Figure 4(a)). The correlation coefficient was greater than 0.999 and the qe value (81.3 mg g-1) estimated from pseudo-second-order model was in
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accord with the experimental qe value (80.0 mg g-1), indicating that the adsorption process follows a pseudo-second-order mechanism and the adsorption mainly belongs to the chemical adsorption. Furthermore, it can be seen from Figure 4(b) that there is a rapid dye uptake with the adsorption equilibrium being reached within 12 minutes and the saturation removal rate of the Ph-PPh3-KAP for acid orange 74 being 96%. 3.3 Adsorption mechanism 7
To explore the possible adsorption mechanism of the Ph-PPh3-KAP, it was used to extract five different types of aromatic compounds including some phthalate esters, PUHs, carbamates, benzoylurea insecticides and chlorophenols. In the investigation, 100.0 mL distilled water was individually spiked with each of the above mentioned four types of compounds at 100.0 ng mL-1, and then the spiked solution was passed through the Ph-PPh3-KAP-packed cartridge at a flow rate of 3.0 mL min-1, respectively. After the cartridge was dried under vacuum for 5 min, 1.2 mL of the respective eluents (acetonitrile for PUHs, benzoylurea insecticides and phthalate esters, methanol
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for carbamates, and alkaline methanol for chlorophenols) was used to desorb the corresponding target analytes from the cartridge. As can be seen from Table S1, the Ph-PPh3-KAP had quite good
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extraction efficiencies for all these tested compounds with the recoveries ranging from 60 to 99%, depending on the compounds. Although the logKOW values of both the PUHs (2.03-2.66) and the carbamates (1.72-2.86) are similar to those of the chlorophenols (2.16-2.80), the recoveries of both the PUHs (97.4-98.6%) and the carbamates (87.6-99.0%) are higher than those of the chlorophenols
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(82.1-89.7%), suggesting that hydrogen bonding mainly contributes to the adsorption because there
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are more hydrogen bond sites in both the PUHs (4-5) and the carbamates (4-5) than that in the chlorophenols (2). For the four phthalate esters, although they have the same number of hydrogen
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bond sites (4), the changes of their extraction recoveries from 98.6 to 72.6% are negatively related
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to their logKOW values from 2.38 to 4.61, suggesting that the polar interactions also is a factor for the adsorption. The similar results for the benzoylurea insecticides further confirm the effect of the
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polar interactions on the adsorption. In summary, the adsorption of the Ph-PPh3-KAP for the analytes was affected by both hydrogen bonding and polar interactions.
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3.4 Establishment of the SPE for the PUHs
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PUHs are widely used to control weeds in agriculture. Since they are hard to degrade, they can exist in the environment and food for a long time, thus posing a carcinogenic hazard to humans [37]. Thus, it is of great importance to develop sensitive methods for the determination of them. Considering that Ph-PPh3-KAP has excellent adsorption ability towards the PUHs by our above
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experiments, some PUHs were selected as the target analytes for the real applications of the Ph-PPh3-KAP-based SPE. 3.4.1 Comparison with other adsorbents An efficient SPE adsorbent is crucial for the SPE of some specific compounds. To justify the selection of the Ph-PPh3-KAP as the adsorbent for the PUHs, the commercial adsorbents including, 8
C18, multi-walled carbon nanotubes (MWCNTs), graphitized carbon black (GCB) and hypercrosslinked polystyrene polymer (PS) were selected for comparison. In the study, 15 mg each of the above adsorbents was weighed accurately and packed into 3-mL SPE cartridges. Then, aliquots of 100 mL aqueous solution spiked with 40.0 ng mL-1 each of the PUHs were passed through the respective cartridges. The adsorbed analytes on different adsorbents were then desorbed with two different eluents which were optimized for each adsorbent, i.e., 1.2 mL acetonitrile for PS, C18, MWCNTs, Ph-PPh3-KAP, and 1.2 mL acetone for GCB. All the experiments were conducted
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in triplicate. The results in Figure 5(a) show that the extraction efficiency of the Ph-PPh3-KAP are higher than any of the other adsorbents, suggesting that the Ph-PPh3-KAP is a favorable adsorbent
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for the PUHs. 3.4.2 Optimization of SPE conditions
In order to achieve a high SPE efficiency for the five PUHs (monuron, metoxuron,
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chlortoluron, monolinuron and buturon), some key experimental factors, such as the pH of sample
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solution, the sample volume, the type of eluent solvent and the eluent volume, were optimized. 100
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mL distilled water spiked with 40.0 ng mL-1 each of the PUHs was used for the optimization
3.4.2.1 Effect of sample solution pH
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experiments.
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In this work, the effect of sample solution pH on the extraction efficiency was investigated by adjusting the pH of the sample solution from 2 to 12 with either 1.0 mol mL-1 HCl or 1.0 mol mL-1
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NaOH solution. Figure 5(b) shows that the extraction efficiency had no evident changes when the sample solution pH varied from 2 to 12. Since the pH values for the water, cucumber and tomato
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sample solutions were about 6.5, the pH of sample solution was not adjusted for the following experiments.
3.4.2.2 Effect of loading rate
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In SPE, the loading rate of the sample solution affects both the entire analysis time and the
recoveries of the analytes. To enable rapid and sensitive analysis, the loading rate was optimized. Figure 5(c) shows that there were no obvious changes in the peak areas of the five PUHs when the sample loading rate was changed from 1 mL min-1 to 10 mL min-1, illustrating that rapid adsorption kinetics exists between the adsorbent and the analytes. On the basis of the above results and to make the analysis time as short as possible, the sample loading rate was chosen at 10 mL min-1. 9
3.4.2.3 Effect of sample volume At a fixed concentration of the analytes, the adsorbed analytes in the SPE cartridge will gradually become saturated with increased sample volume. The sample volume at the saturation point is called the penetration volume. When the sample volume is above the penetration volume, the SPE recoveries will decrease. Therefore, different volumes of the sample solution (50, 100, 150, 200, 300 mL) were tested for the Ph-PPh3-KAP packed SPE cartridge. The results in Figure 5(d)
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show that there were no significant differences in the extraction efficiency of the analytes when the sample volume was increased from 50.0 mL to 300.0 mL, indicating that 300 mL has not yet reached its penetration volume. Considering that a large sample volume will require large amount
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of sample and long analysis time, 100.0 mL sample solution was chosen for the subsequent experiments.
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3.4.2.4 Effect of the type and volume of elution solvent
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In order to elute the adsorbed analytes as completely as possible, it is necessary to select an appropriate elution solvent and its volume. In this work, the three commonly used organic solvents
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(methanol, acetonitrile and acetone) were tested as the elution solvent. Figure 5(e) shows that
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acetonitrile had the best desorption efficiency for all of the PUHs. Consequently, acetonitrile was chosen as the eluent. Then, the volume of acetonitrile was further optimized for a complete
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desorption of the PUHs. Figure 5(f) shows that the extraction recoveries were increased when the acetonitrile volume was increased from 0.3 to 1.0 mL, and remained almost unchanged when the eluent volume was changed from 1.0 to 1.2 mL, indicating that 1.0 mL acetonitrile was required for
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the complete elution of the PUHs. Thus, 1.0 mL of acetonitrile was selected in the subsequent experiments. Experimental results showed that after the used cartridge was further washed with 0.3
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mL acetonitrile, no carry-over was observed. Therefore, after the used cartridge was washed with 0.3 mL acetonitrile and 2 mL distilled water, it can be reused for the next extraction. The experimental results showed that the Ph-PPh3-KAP-packed SPE cartridge can be reused at least 30
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times without a significant decrease in extraction efficiency. 3.5 Adsorption capacity In order to explore the adsorption capacity of the Ph-PPh3-KAP, 100 mL aqueous solution spiked with each of the PUHs at three levels (0.040 µg mL-1, 2.0 µg mL-1 and 4.0 µg mL-1) was subjected to the SPE and analysis. The maximum adsorption capacity of the Ph-PPh3-KAP was 10
measured to be 16.6 mg g-1 for metoxuron, 16.1mg g-1 for monuron, 18.4 mg g-1 for chlorotoluron, 17.3 mg g-1 for monolinuron, and 24.2 mg g-1 for buturon, respectively. These values are bigger than those reported in the literature [38], suggesting that the Ph-PPh3-KAP has a strong adsorption capability for the PUHs. 3.6 Evaluation of the method
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Under the optimized conditions, the linear range, correlation coefficient (r), limits of detection (LODs, S/N=3), limits of quantitation (LOQs, S/N=9), and relative standard deviations (RSDs) of the method for the determination of the PUHs were investigated. For the elimination of the matrix
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effect, the matrix-matched calibrations were established by spiking the PUHs into the PUHs-free lake water, cucumber and tomato samples at different levels (0.1, 0.5, 1.0, 5.0, 10.0, 20.0, 40.0, 100.0 ng mL-1 for lake water, and 0.5, 1.0, 5.0, 10.0, 20.0, 40.0, 100.0 ng g-1 for cucumber and tomato samples). The results are shown in Table 1. For the lake water sample, a good linearity for
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metoxuron (r = 0.9999) was obtained in the range of 0.5-100 ng mL-1, and the LODs (S/N = 3) was
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0.02 ng mL-1 with the RSD at about 3.4%. The other four analytes had a good linearity (r> 0.9997)
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in the range of 0.1-100 ng mL-1 with the LODs between 0.01 and 0.02 ng mL-1 and the RSDs between 3.3 and 3.8%. For the tomato and the cucumber samples, the analytes gave a good linear
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response in the range of 0.5-100.0 ng g-1 with r between 0.9973 and 0.9999. The LODs were in the range of 0.03-0.05 ng g-1 for tomato and cucumber samples. The RSDs obtained by determining the
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PUHs-spiked samples at 5.0 ng g-1 were 4.0-6.1% for tomato sample and 4.8-6.0% for cucumber sample, indicating a good repeatability of the method.
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3.7 Analysis of real samples
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In order to study the practical applicability of the method, the residues of the PUHs in lake water, cucumber and tomato samples were analyzed by the current method, and the results are summarized in Table 2. As shown in Table 2, chlortoluron was found at about 0.15 ng g-1 in the tomato sample and metoxuron was detected at a concentration lower than its LOQ in the cucumber
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sample. Since no relevant reference sample is available for the validation of the method, spiked samples were prepared for recovery studies to check the accuracy of the method. The lake water was spiked with the analytes at three fortification levels of 0.5, 1.0, 10.0 ng mL-1 and the cucumber and tomato samples were spiked with the analytes at 0.5, 5.0 and 20.0 ng g-1, respectively. Then the spiked samples were analyzed by the developed method. The measured recoveries for the five PUHs ranged from 80.8% to 118% with RSDs between 2.9% and 11.5%, indicating that the method 11
has a quite good accuracy and precision. Figure 6 shows the chromatograms of the tomato and the cucumber samples with and without the analytes being spiked. 3.8 Comparison with literature methods The current method was compared with other reported methods [38-42] in the respect of the adsorbent material used, samples, linear range, LODs and RSDs. The comparison results in Table
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S2 show that the current method had comparable or lower LODs, and a better repeatability than other methods. In addition, the Ph-PPh3-KAP demonstrated rapid adsorption/desorption kinetics and large adsorption capacity toward the PUHs. However, in the preparation of the Ph-PPh3-KAP,
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after the reaction catalyzed by FeCl3, a time-consuming washing through Soxhlet extraction was needed to remove the catalysts, byproducts and unreacted monomers. 4 Conclusions
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In this work, a triphenylphosphine-based knitting aryl network polymer, Ph-PPh3-KAP, was
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investigated as the SPE adsorbent for the first time. It showed an excellent adsorption capability
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towards a variety of benzene ring-containing compounds. The possible adsorption mechanism was attributed to both hydrogen bonding and polar interactions between the Ph-PPh3-KAP and analytes.
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The Ph-PPh3-KAP was successfully applied to extract the PUHs residues from real samples with a satisfactory result. The current work indicates that the Ph-PPh3-KAP has a great application
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Acknowledgments
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potential as the SPE adsorbent for other applications.
Financial supports from the National Natural Science Foundation of China (31471643,
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31571925, 31671930), the Natural Science Foundation of Hebei Province (B2016204136, B2016204146, B2017204025), the Advance Program for the Introduction of Overseas Scholars by Hebei Province (CL201713), the Hebei “Double First Class Discipline” Construction Foundation for the Discipline of Food Science and Engineering of Hebei Agricultural University
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(2016SPGCA18), the Scientific and Technological Research Foundation of the Department of Education of Hebei Province (ZD2016085) and the Natural Science Foundation of Hebei Agricultural
University
(LG201607
LG201610,
acknowledged. References 12
ZD201703,
LG201712)
are
gratefully
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Macromol Rapid Comm. 34(6) (2013) 471-484. [14] B. Li, R. Gong, W. Wang, X. Huang, Z. Wang, H. Li, C. Hu, B. Tan, A new strategy to microporous polymers: knitting rigid aromatic building blocks by external cross-linker, Macromolecules. 44(8) (2011) 2410-2414. [15] L. Tan, B. Tan, Hypercrosslinked porous polymer materials: design, synthesis, and applications, Chem Soc Rev. 46(11) (2017) 3322-3356. 13
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Kupgan,
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[19] J. Germain, J. Hradil, J.M.J. Fréchet, F. Svec, High surface area nanoporous polymers for reversible hydrogen storage, Chem Mater. 18(18) (2006) 4430-4435.
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[21] Wang, Chang-An, Wei, Advances in porous organic catalysis, Acta Chim Sinica. 73(6) (2015)
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Chem A. 2(21) (2014) 8054-8059.
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microporous organic polymer networks based on tetraphenylethylene for CO2 capture, J Mater
[23] S. Xu, K. Song, T. Li, B. Tan, Palladium catalyst coordinated in knitting N-heterocyclic
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carbene porous polymers for efficient Suzuki-Miyaura coupling reactions, J Mater Chem A. 3(3) (2014) 1272-1278.
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[24] B. Li, Z. Guan, W. Wei, X. Yang, J. Hu, B. Tan, L. Tao, Highly dispersed Pd catalyst locked in knitting aryl network polymers for Suzuki-Miyaura coupling reactions of aryl chlorides in aqueous media, Adv Mater. 24(25) (2012) 3390-3395.
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[26] F. Maya, F. Svec, A new approach to the preparation of large surface area poly(styrene-co-divinylbenzene) monoliths via knitting of loosechains using external crosslinkers and application of thesemonolithiccolumns forseparation of small molecules, Polymer. 55(1) (2014) 340-346. [27] C. Lu, S. Liu, J. Xu, Y. Ding, G. Ouyang, Exploitation of a microporous organic polymer as a stationary phase for capillary gas chromatography, Anal Chim Acta. 902 (2016) 205-211. 14
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of phenylurea herbicides is equally predictable by concentration addition and independent action, Environ Toxicol Chem. 23(2) (2004) 258-264. [38] X. Liang, J. Wang, Q. Wu, C. Wang, Z. Wang, Use of a hypercrosslinked triphenylamine polymer as an efficient adsorbent for the enrichment of phenylurea herbicides, J Chromatogr A. 1538 (2018) 1-7.
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[39] S. Gao, J. You, X. Zheng, Y. Wang, R. Ren, R. Zhang, Y. Bai, H. Zhang, Determination of phenylurea and triazine herbicides in milk by microwave assisted ionic liquid microextraction high-performance liquid chromatography, Talanta 82(4) (2010) 1371-1377. [40] Y. Hu, Simultaneous determination of phenylurea herbicides in yam by capillary electrophoresis with electrochemiluminescence detection, J Chromatogr B. s 986-987 (2015) 143-148. [41] X. Dong, S. Liang, Z. Shi, H. Sun, Development of multi-residue analysis of herbicides in
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cereal grain by ultra-performance liquid chromatography-electrospray ionization-mass spectrometry, Food Chem. 192 (2016) 432-440.
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[42] S.L. Lin, Y.R. Wu, M.R. Fuh, Polymer monolith microextraction using poly(butyl methacrylate- co -1,6-hexanediol ethoxylate diacrylate) monolithic sorbent for determination of
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N
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phenylurea herbicides in water samples, Talanta. 147 (2016) 199-206.
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Figure Captions Figure 1 Scheme for the synthesis of the Ph-PPh3-KAP. Figure 2 The FT-IR spectrum (a), the nitrogen adsorption-desorption isotherms and pore size
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distribution curve (b), the SEM image (c), and the TG graph (d) for the Ph-PPh3-KAP. Figure 3 Dye color changes by the adsorption of the Ph-PPh3-KAP. (a) acid fuchsin; (b) acid orange 74; (c) congo red; (d) malachite green. For each dye, three different vials represent the dye
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solution (left), dye solution with the adsorbent (middle) and the dye solution after the removal of the adsorbent (right).
Figure 4 The pseudo-second-order kinetics of the acid orange 74 by the Ph-PPh3-KAP (a) and the
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adsorption equilibrium curve (b).
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Figure 5 Comparison of different adsorbents (a); the effect of the sample solution pH (b), sample
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loading rate (c), sample volume (d), the eluent type (e) and the eluent volum (f).
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Figure 6 (a) The typical chromatograms of cucumber sample (bottom) and the cucumber sample spiked with the PUHs at each concentration of 0.5 ng g-1 (top); (b) the tomato sample (bottom) and
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the tomato sample spiked with the PUHs at each concentration of 0.5 ng g-1 (top). Peak identification: 1. Metoxuron; 2. Monuron; 3. Chlortoluron; 4. monolinuron; 5. Buturon. Mobile phase: acetonitrile-water (36:64 v/v) for (a), acetonitrile-water (40:60 v/v) for (b). Detection
A
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wavelength: 244 nm.
17
+
PPh3
FDA
Ph-PPh3-KAP
Scheme for the synthesis of the Ph-PPh3-KAP.
A
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A
N
U
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Figure 1
+
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Ph
18
400
0.80
300
0.60
4000
O-H
)
0
0 3000
2000
-1
Wavenumber (cm
1000
0.0
0.2
)
100
0.6
0.8
1.0
Relative pressure (P/P0)
D
350oC
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80 60
N
Weight Loss (%)
0.4
10 20 30 40 50 Pore width (nm)
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0.55
100
0.12 0.10 0.08 0.06 0.04 0.02 0.00
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P-CH2
3
1437
0.65
200
(
C-H
C-H
dv/dw cm /g nm
C-H
0.70
3
0.75
N2 adsorbed (cm /g)
Transmittance (a.u.)
0.85
40
M
A
20 0
0
100
200
300
400
500 o
Temperature ( C)
600
700
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Figure 2 The FT-IR spectrum (a), the nitrogen adsorption-desorption isotherms and pore size
A
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distribution curve (b), the SEM image (c), and the TG graph (d) for the Ph-PPh3-KAP.
19
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Figure 3 Dye color changes by the adsorption of the Ph-PPh3-KAP. (a) acid fuchsin; (b) acid
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orange 74; (c) congo red; (d) malachite green. For each dye, three different vials represent the dye solution (left), dye solution with the adsorbent (middle) and the dye solution after the removal of
A
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PT
ED
M
A
N
U
the adsorbent (right).
20
100
0.24 0.16 0.08 0.00
0
5
10
15
Time (min)
20
25
30
80 60 40 20 0
0
5
10
15
Time (min)
20
25
30
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-1
t/qt(min g mg )
Removal rate(%)
0.32
Figure 4 The pseudo-second-order kinetics of the acid orange 74 by the Ph-PPh3-KAP (a) and the
A
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PT
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M
A
N
U
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adsorption equilibrium curve (b).
21
(b)
Peak area(1.010 )
7 5
5
Peak area (1.010 )
4
8
(a)
3 2 1 0
6 5 Metoxuron Monuron Chlortoluron Monolinuron Buturon
4 3 2
KAP
C18
GCB
MWNTs
2
PS
4
6
8
(c)
100
pH
8
10
(d)
7
4 3
1 methanol
150
0.6
0.8
100
200
300
N 100
5
2
50
Sample volume (mL)
M
5
(e)
6
0
0
1 5 10 -1 8 Sample solution flow rate (mL min )
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7
40
(f)
A
8
60
20
acetonitrile
Recovery(%)
2
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Metoxuron Monuron Chlortoluron Monolinuron Buturon
4 3
Peak area (1.010 )
Recovery(%)
5
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Peak area10
5
80 6
12
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Comparison of different adsorbents
80 60 40 20 0
acetone
0.3
1.0
1.2
The volum of eluent (mL)
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The type of eluent
Figure 5 Comparison of different adsorbents (a); the effect of the sample solution pH (b), sample
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loading rate (c), sample volume (d), the eluent type (e) and the eluent volum (f).
22
b
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a
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Figure 6 (a) The typical chromatograms of cucumber sample (bottom) and the cucumber sample spiked with the PUHs at each concentration of 0.5 ng g-1 (top); (b) the tomato sample (bottom) and the tomato sample spiked with the PUHs at each concentration of 0.5 ng g-1 (top). Peak
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identification: 1. Metoxuron; 2. Monuron; 3. Chlortoluron; 4. monolinuron; 5. Buturon. Mobile
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phase: acetonitrile-water (36:64 v/v) for (a), acetonitrile-water (40:60 v/v) for (b). Detection
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wavelength: 244 nm.
23
Table
Table 1 The linear range (LR), correlation coefficients (r), limits of detection (LODs), limits of quantitation (LOQs) and relative standard deviations (RSDs) for lake water, cucumber and tomato samples.
Cucumber
Metoxuron
0.1-100.0
0.9999
3.4
0.02
Monuron
0.1-100.0
0.9999
3.6
0.02
Chlortoluron
0.1-100.0
0.9999
3.8
Monolinuron
0.1-100.0
0.9998
3.3
Buturon
0.1-100.0
0.9997
3.7
Metoxuron
0.5-100.0
0.9993
4.0
Monuron
0.5-100.0
0.9996
5.7
Chlortoluron
0.5-100.0
0.9989
6.0
Monolinuron
0.5-100.0
0.9988
Buturon
0.5-100.0
0.9994
Metoxuron
0.5-100.0
Monuron
0.5-100.0
Chlortoluron Monolinuron Buturon
LOQs (ng mL-1 or ng g-1)
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LODs (ng mL-1 or ng g-1)
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RSD (%) (n = 5)
0.06 0.06 0.03
0.02
0.06
0.02
0.06
0.05
0.15
0.05
0.15
0.03
0.09
5.6
0.05
0.15
6.1
0.05
0.15
0.9995
6.0
0.05
0.15
0.9989
4.8
0.05
0.15
0.5-100.0
0.9992
5.9
0.03
0.09
0.5-100.0
0.9973
5.0
0.05
0.15
N
U
0.01
A
Tomato
r
M
Lake water
LR (ng mL-1 or ng g-1)
Analytes
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Samplesa
0.5-100.0 0.9997 5.0 0.05 0.15 -1 a For lake water sample, the unit of the LR, LOD and LOQ for the analytes is ng mL ; for tomato and cucumber
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samples, the unit of the LR, LOD and LOQ for the analytes is ng g-1.
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Table 2 Analytical results for the determination of the PUHs in lake water, cucumber and tomato samples.
Found (ng g-1)
0.0
ndb
0.5
0.53
106
1.0
0.92
10.0
9.88
0.0
nd
0.5
0.44
87.4
1.0
0.97
10.0
10.2
0.0
nd
0.5
0.44
87.3
9.10
0.5
1.0
1.18
118
3.99
5.0
10.0
10.2
102
3.01
0.0
nd
0.5
0.51
101
1.0
0.81
10.0
9.91
0.0
nd
0.5
0.46
91.6
1.01
101
R (%)
RSDs (%)
0.0
nd
10.0
0.5
0.46
92.9
9.14
91.6
4.86
5.0
5.43
109
3.95
98.8
3.43
20.0
20.0
100
4.05
0.0
nd
5.82
0.5
0.40
97.1
4.49
5.0
5.30
102
2.90
20.0
19.9
0.0
~0.15
Found (ng g-1)
R (%)
RS Ds (%)
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RSDs (%)
0.41
81.9
5.36
5.38
108
6.00
20.0
99.8
4.05
nd
80.8
11.0
0.43
86.7
9.5
106
5.74
5.54
111
4.78
99.4
3.86
19.8
98.8
4.22
nd 11.5
0.51
101
4.47
5.53
111
6.00
5.32
106
5.92
20.0
19.8
99.1
4.16
20.2
101
3.51
0.0
nd
6.75
0.5
0.49
97.8
5.34
0.45
90.9
5.92
80.9
3.83
5.0
5.42
108
5.59
5.35
107
5.04
99.1
3.20
20.0
19.8
98.8
4.24
19.5
97.7
3.67
0.0
nd
11.3
0.5
0.49
98.4
5.12
0.55
110
6.21
6.21
5.0
5.28
106
6.05
5.11
102
4.96
10.0 10.0 100 3.88 Ra: recovery of the method; ndb: not detected.
20.0
19.8
99.2
3.84
19.7
98.3
4.05
Buturon
A
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1.0
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Monolinuron
A
98.9
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0.49
M
Chlortoluron
Ra (%)
SC R
Monuron
Found (ng mL-1)
Cucumber sample (n = 5)
Spiked (ng g-1)
U
Metoxuron
Spiked (ng mL-1)
Tomato sample (n = 5)
N
Analytes
Water sample (n = 5)
25
nd
nd
S0021-9673(18)31177-4 https://doi.org/10.1016/j.chroma.2018.09.026 CHROMA 359691
To appear in:
Journal of Chromatography A
Received date: Revised date: Accepted date:
14-6-2018 8-9-2018 15-9-2018
Please cite this article as: Wang Q, Zhang L, Hao L, Wang C, Wu Q, Wang Z, Phosphorous-enriched knitting aryl network polymer for the rapid and effective adsorption of aromatic compounds, Journal of Chromatography A (2018), https://doi.org/10.1016/j.chroma.2018.09.026 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Phosphorous-enriched knitting aryl network polymer for the rapid and effective adsorption of aromatic compounds
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College of Science, Hebei Agricultural University, Baoding 071001, China
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Qianqian Wang, Lihong Zhang, Lin Hao, Chun Wang, Qiuhua Wu*, Zhi Wang*
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Correspondence: Professor Qiuhua Wu, College of Science, Hebei Agricultural University, Baoding 071001, Hebei, China; Tel: +86-312-7528291; Fax: +86-312-7528292; E-mail: [email protected]. Correspondence: Professor Zhi Wang, College of Science, Hebei Agricultural University, Baoding 071001, Hebei, China; Tel: +86-312-7521513; Fax: +86-312-7521513; E-mail: [email protected].
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Highlights
A phosphorous-enriched knitting aryl network (Ph-PPh3-KAP) was prepared.
The Ph-PPh3-KAP showed excellent adsorption ability to aromatic compounds.
A sensitive method was developed for analyzing phenylurea pesticides in real
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samples.
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The Ph-PPh3-KAP can serve as a promising adsorbent for other applications.
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ABSTRACT A phosphorous-enriched knitting aryl network polymer (named as Ph-PPh3-KAP) was fabricated by one-step crosslinking between triphenylphosphine and benzene, with formaldehyde dimethyl acetal as an external crosslinker. The Ph-PPh3-KAP had a large surface area and good
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physicochemical stability. Its adsorption performance for aromatic organic compounds was evaluated by using some dyes and benzene ring-containing compounds as the model adsorbates. The results exhibited that it had a rapid and effective adsorption for the aromatic organic
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compounds due to the hydrogen bonding and polar interactions of the Ph-PPh3-KAP with the target compounds. Then, the Ph-PPh3-KAP was explored as the adsorbent for the solid phase extraction of some phenylurea pesticides from lake water, tomato and cucumber samples prior to HPLC analysis. Under optimal conditions, the linear responses of the phenylurea pesticides were 0.1-100 ng mL-1
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for lake water and 0.5-100 ng g-1 for cucumber and tomato samples. The limits of detection for the
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analytes at S/N = 3 were 0.01-0.02 ng mL-1 for lake water and 0.03-0.05 ng g-1 for cucumber and
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tomato samples. The recoveries were in the range from 80.8% to 118%. The Ph-PPh3-KAP
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exhibited a great application potential for extraction of aromatic compounds.
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Keywords: Knitting aryl network polymer, Solid phase extraction adsorbent, Phenylurea pesticides
2
1 Introduction The porous organic framework (POF) materials, with their large surface area and high physicochemical stability, have attracted enormous scientific attention because of their diverse application potentials in gas storage and separation [1, 2], heterogeneous catalysis [3], sensor [4-6] and removal of heavy metal ions [7]. Over the last few decades, the research in developing so useful
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POFs has resulted in a lot of novel organic porous materials including hyper-crosslinked polymers (HCPs) [8], polymer of intrinsic microporosity (PIMs) [9], conjugated microporous polymers (CMPs) [10] and covalent organic frameworks (COFs) [11]. Among them, HCPs have recently
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undergone a rapid development as a promising class of microporous materials and become widely focused materials because of their low cost, simple and versatile synthesis. HCPs are primarily synthesized by three methods: (1) post-crosslinking polymer precursors [12], (2) direct one-step polycondensation of functional monomers [13], and (3) knitting rigid aromatic building blocks with
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external crosslinkers to obtain knitting aromatic polymers (KAPs) [14]. Compared with the first two
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methods, the knitting strategy which was first developed by Tan and co-workers in 2011 for the
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preparation of KAPs is a breakthrough [14], in which formaldehyde dimethyl acetal (FDA) was used as a crosslinker to link simple aromatic compounds like benzene or biphenyl with rigid
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methylene bridges through the Friedel-Crafts reaction catalyzed by anhydrous FeCl3. The knitting strategy allows the use of a wide variety of aromatic building blocks containing different functional
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groups such as methylbenzene, chlorobenzene and phenols [15, 16], and it also allows the use of heterocyclic aromatic building blocks such as furan, thiophene and pyrrole [17], thereby increasing
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the diversity and the functionality of the KAPs. Moreover, by changing the molar ratio of crosslinkers to monomers, the inner skeleton of the KAPs can be easily adjusted [13, 18], thus
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resulting in an abundant porous structure and high surface area. Since the knitting strategy has such outstanding characteristics, it has been developed rapidly and has become a platform to prepare new porous materials with diverse structure, composition and functionality [19, 20]. As a new class of organic porous material, KAPs have caught a lot of research attention, and
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some of them have been successfully applied in gas storage [21, 22], heterogeneous catalysis [23, 24], and separation and purification [25, 26]. The KAP with benzene as the monomer and FDA as the crosslinker has been used as stationary phase for capillary gas chromatography [27] and electrochromatography [28], displaying a potential applicability of KAPs in the adsorption and separation field. Since KAPs possess extended π-electron system and highly stable conjugated structure, they are expected to have a strong adsorption affinity toward aromatic compounds by 3
π-stacking effect, making them possible to be superior adsorbents for aromatic organic compounds. Nevertheless, so far, the applications of KAPs as adsorbent still remain rarely exploited [16]. Very recently, a novel functionalized KAP (Ph-PPh3) was prepared by knitting triphenylphosphine (PPh3) with benzene [24, 29] for the use as catalyst support. Since the KAP Ph-PPh3 contains large π-electron conjugated system and many P atoms, it should have the capability to effectively adsorb some compounds by π-π stacking and polar interactions. However, so far there have been no reports for its applications in analytical chemistry.
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In this work, the Ph-PPh3-KAP was prepared by using PPh3 and benzene as building blocks and FDA as an external crosslinker [24]. To explore its adsorption capability, the Ph-PPh3-KAP
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was investigated as the adsorbent for the first time with some aromatic organic compounds including some dyes (acid fuchsin, acid orange 74, congo red and malachite green), phenylurea herbicides (PUHs), benzoylurea insecticides, phthalate esters, carbamate insecticides and chlorophenols as model adsorbates. The Ph-PPh3-KAP showed rapid adsorption kinetics and large
the
Ph-PPh3-KAP
as
the
adsorbent
coupled
with
high
performance
liquid
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with
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adsorption ability toward the aromatic compounds. Finally, a solid-phase extraction (SPE) method
chromatography-ultraviolet detection (HPLC-UV) was established for the determination of five
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PUHs (metoxuron, monuron, chlortoluron, monolinuron and buturon) in lake water, cucumber and
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tomato samples.
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2 Experimental
The description about the reagents and apparatus is provided in the Electronic Supporting
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Material (ESM).
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2.1 Synthesis of Ph-PPh3-KAP
Ph-PPh3-KAP was prepared according to the method reported in the previous literature [24].
Briefly, 9.75 g anhydrous ferric chloride and 1.56 g benzene were added to 20 mL dichloroethane solution containing 5.25 g triphenylphosphine and 4.56 g FDA. After the mixture was heated at 45 o
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C for 5 h under magnetic stirring to form a primary network, the reaction temperature was raised
to 80 oC for 12 h to finish the cross-linking procedure (a condenser was used for reflux). After cooling, the resulting solid product was obtained by filtration and then thoroughly washed with methanol until the filtrate turned clear. After the solid product was further purified by Soxhlet extraction with methanol for 24 h and vacuum dried at 60 oC for 24 h, the final Ph-PPh3-KAP was obtained. The scheme for the synthesis of the Ph-PPh3-KAP is shown in Figure 1. 4
2.2 Adsorption kinetics The adsorption kinetic studies were performed as follows: 30 mg of the Ph-PPh3-KAP was put into 50 mL dye solution with its initial concentration at 50 mg L-1. Then, the mixture was shaken on a slow-moving platform shaker. At the interval of an appropriate time, the Ph-PPh3-KAP adsorbent was removed from the solution by filtration, and the residual dye concentration in the filtrate was
by the Ph-PPh3-KAP was calculated according to the following equations: C0 Ct V m
qe
C0 C e V m
(1)
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qt
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determined with a UV-visible spectrophotometer at 478 nm (λmax). The removed quantity of the dye
(2)
where qt (mg g-1) and qe (mg g-1) represent the removed quantity of the dye by the Ph-PPh3-KAP at
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any time t (min) and at equilibrium, respectively; C0, Ct and Ce (mg L-1) stand for the dye
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concentration at the initial, at any time t and at equilibrium, respectively; V (L) is the volume of the
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solution; m (g) is the mass of the Ph-PPh3-KAP.
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2.3 Sample preparation
The tomato or cucumber sample was homogenized by a laboratory homogenizer. Then 50.0 g
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of the homogenized sample was weighed and put into two 50.0-mL plastic centrifugation tubes. After the centrifugation at 5000 rpm for 10 min, the supernatant was transferred into a conical flask.
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Then, the sediment was extracted with 5.0 mL acetonitrile by vortexing it for 3 min and then centrifuged. After all of the supernatants were filtered and transferred to a 100.0-mL volumetric
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flask, the volume was made to the mark with distilled water. Then, the resulting sample solution was used for the subsequent SPE. The lake water was first filtered with 0.45 μm membrane and then used for the following SPE.
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2.4 SPE procedures
15 mg of the Ph-PPh3-KAP was packed in a 3 mL empty SPE cartridge, and then the packed cartridge was conditioned with 6 mL methanol and 6 mL distilled water. Then, 100 mL sample solution was loaded into the cartridge at a flow rate of 10 mL min-1. After the cartridge was washed with 5 mL of acetonitrile-water mixture (10:90, V / V), the SPE cartridge was vacuum dried. Then, 5
the analytes were eluted with 1 mL acetonitrile at the elution rate of 0.5 mL min-1. After being filtered with 0.22 μm membrane, 20 μL of the eluate was analyzed by the HPLC. Before the next extraction, the cartridge was washed successively with 0.3 mL acetonitrile and 2 mL distilled water to ensure that there was no carry-over in the cartridge. 3 Results and discussion
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3.1 Characterization of the Ph-PPh3-KAP Ph-PPh3-KAP was first subjected to FT-IR characterization. Figure 2(a) shows that a series of characteristic bands at 1437, 1600-1450, 1250-950, and 900-650 cm-1 exist, which are consistent
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with the literature report [30], confirming the successful synthesis of the Ph-PPh3-KAP. The peak at 1437 cm-1 corresponds to the vibrations of P-CH2 bond, indicating that the phosphine ligand is embedded in the backbone of the Ph-PPh3-KAP [31]. The peaks at 1600-1450 cm-1 can be attributed
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to the benzene skeleton stretching, and the peaks in the vicinity of 1250-950 cm-1 and 900-650 cm-1 result from the C-H out-of-plane bending and in-plane bending vibrations of the benzene ring,
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respectively [32]. The peak at 3500 cm-1 can be assigned to the O-H stretching vibration coming
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from the water molecules adsorbed by the Ph-PPh3-KAP [16, 33]. In addition, the C-H stretching
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vibration of the methylene bridge bonds can be found from the double peaks at nearly 2900 and 2850 cm-1 [33].
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The nitrogen adsorption-desorption isotherms were measured to investigate the porosity and surface area of the Ph-PPh3-KAP. The surface area of the Ph-PPh3-KAP was measured to be 659 m2 g-1. The adsorption isotherm and pore size distribution of the Ph-PPh3-KAP are shown in Figure
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2(b). A rapid uptake at low relative pressures of 0-0.03 indicates a rich microporous structure, a slight hysteresis loop suggests the existence of some mesopores, and a sharp rise in the relative
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pressures from 0.8 to 1.0 reflects the presence of macropores in the Ph-PPh3-KAP. The Barrett-Joyner-Halenda (BJH) adsorption average pore width was 6.12 nm, and the total pore volume was 0.57 cm3 g-1. The isotherm curves of sorption and desorption were not closed due to the
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pore structure deformation resulting from some degree of the polymer network swelling in liquid nitrogen [34]. The morphology and porous structures of the Ph-PPh3-KAP were observed by both SEM and TEM. Figure 2 (c) and Figure S1 exhibit that the Ph-PPh3-KAP had an amorphous morphology with a porous nature. In addition, the size of Ph-PPh3-KAP particles was measured and Figure S2 shows that the size of Ph-PPh3-KAP was mainly distributed in the range of 0.71-1.99 μm and the average particle size was about 1.35 μm. 6
To examine the thermal stability of the Ph-PPh3-KAP, TGA was performed by heating the Ph-PPh3-KAP from room temperature to 800 oC at a ramping rate of 10 oC min-1 under nitrogen flow. The TG curve in Figure 2(d) shows that the Ph-PPh3-KAP was stable up to 350 °C, displaying an excellent thermal stability [35, 36]. 3.2 Adsorption performance To investigate the adsorption ability of the Ph-PPh3-KAP, the adsorption experiments for
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different dyes were conducted by adding 10 mg of the Ph-PPh3-KAP in 10 mL each of 20 mg L-1 different dyes solutions respectively, including acid fuchsin, acid orange 74, congo red and
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malachite green. As shown in Figure 3, the Ph-PPh3-KAP particles were uniformly dispersed in the dye solutions. The color of the dye solutions became obviously lighter after the mixture was shaken for 5 minutes. In order to clearly observe the adsorption effect, the above dye solutions were filtered and the filtrates were compared with the untreated ones. Obviously, all of the filtrates of the four
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dyes after treatment are clear and colorless, indicating that the Ph-PPh3-KAP can rapidly remove
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the dyes in a short time. Thus, it is expected that the Ph-PPh3-KAP can serve as an adsorbent to
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adsorb some organic compounds.
In order to evaluate the adsorption kinetics of the Ph-PPh3-KAP, the adsorption experiments
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were carried out by using acid orange 74 as a model adsorbate. A pseudo-second-order kinetic
t 1 t 2 qt kqe qe
(3)
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model was used to study the adsorption kinetics, and it is expressed as follows:
Where qe and qt are the amounts of the adsorbed analytes at equilibrium and at any time t,
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respectively, k is the rate constant. The values of k and qe can be obtained from the slope and interception of the linear regression of t/qt versus t (Figure 4(a)). The correlation coefficient was greater than 0.999 and the qe value (81.3 mg g-1) estimated from pseudo-second-order model was in
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accord with the experimental qe value (80.0 mg g-1), indicating that the adsorption process follows a pseudo-second-order mechanism and the adsorption mainly belongs to the chemical adsorption. Furthermore, it can be seen from Figure 4(b) that there is a rapid dye uptake with the adsorption equilibrium being reached within 12 minutes and the saturation removal rate of the Ph-PPh3-KAP for acid orange 74 being 96%. 3.3 Adsorption mechanism 7
To explore the possible adsorption mechanism of the Ph-PPh3-KAP, it was used to extract five different types of aromatic compounds including some phthalate esters, PUHs, carbamates, benzoylurea insecticides and chlorophenols. In the investigation, 100.0 mL distilled water was individually spiked with each of the above mentioned four types of compounds at 100.0 ng mL-1, and then the spiked solution was passed through the Ph-PPh3-KAP-packed cartridge at a flow rate of 3.0 mL min-1, respectively. After the cartridge was dried under vacuum for 5 min, 1.2 mL of the respective eluents (acetonitrile for PUHs, benzoylurea insecticides and phthalate esters, methanol
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for carbamates, and alkaline methanol for chlorophenols) was used to desorb the corresponding target analytes from the cartridge. As can be seen from Table S1, the Ph-PPh3-KAP had quite good
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extraction efficiencies for all these tested compounds with the recoveries ranging from 60 to 99%, depending on the compounds. Although the logKOW values of both the PUHs (2.03-2.66) and the carbamates (1.72-2.86) are similar to those of the chlorophenols (2.16-2.80), the recoveries of both the PUHs (97.4-98.6%) and the carbamates (87.6-99.0%) are higher than those of the chlorophenols
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(82.1-89.7%), suggesting that hydrogen bonding mainly contributes to the adsorption because there
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are more hydrogen bond sites in both the PUHs (4-5) and the carbamates (4-5) than that in the chlorophenols (2). For the four phthalate esters, although they have the same number of hydrogen
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bond sites (4), the changes of their extraction recoveries from 98.6 to 72.6% are negatively related
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to their logKOW values from 2.38 to 4.61, suggesting that the polar interactions also is a factor for the adsorption. The similar results for the benzoylurea insecticides further confirm the effect of the
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polar interactions on the adsorption. In summary, the adsorption of the Ph-PPh3-KAP for the analytes was affected by both hydrogen bonding and polar interactions.
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3.4 Establishment of the SPE for the PUHs
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PUHs are widely used to control weeds in agriculture. Since they are hard to degrade, they can exist in the environment and food for a long time, thus posing a carcinogenic hazard to humans [37]. Thus, it is of great importance to develop sensitive methods for the determination of them. Considering that Ph-PPh3-KAP has excellent adsorption ability towards the PUHs by our above
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experiments, some PUHs were selected as the target analytes for the real applications of the Ph-PPh3-KAP-based SPE. 3.4.1 Comparison with other adsorbents An efficient SPE adsorbent is crucial for the SPE of some specific compounds. To justify the selection of the Ph-PPh3-KAP as the adsorbent for the PUHs, the commercial adsorbents including, 8
C18, multi-walled carbon nanotubes (MWCNTs), graphitized carbon black (GCB) and hypercrosslinked polystyrene polymer (PS) were selected for comparison. In the study, 15 mg each of the above adsorbents was weighed accurately and packed into 3-mL SPE cartridges. Then, aliquots of 100 mL aqueous solution spiked with 40.0 ng mL-1 each of the PUHs were passed through the respective cartridges. The adsorbed analytes on different adsorbents were then desorbed with two different eluents which were optimized for each adsorbent, i.e., 1.2 mL acetonitrile for PS, C18, MWCNTs, Ph-PPh3-KAP, and 1.2 mL acetone for GCB. All the experiments were conducted
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in triplicate. The results in Figure 5(a) show that the extraction efficiency of the Ph-PPh3-KAP are higher than any of the other adsorbents, suggesting that the Ph-PPh3-KAP is a favorable adsorbent
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for the PUHs. 3.4.2 Optimization of SPE conditions
In order to achieve a high SPE efficiency for the five PUHs (monuron, metoxuron,
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chlortoluron, monolinuron and buturon), some key experimental factors, such as the pH of sample
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solution, the sample volume, the type of eluent solvent and the eluent volume, were optimized. 100
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mL distilled water spiked with 40.0 ng mL-1 each of the PUHs was used for the optimization
3.4.2.1 Effect of sample solution pH
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experiments.
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In this work, the effect of sample solution pH on the extraction efficiency was investigated by adjusting the pH of the sample solution from 2 to 12 with either 1.0 mol mL-1 HCl or 1.0 mol mL-1
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NaOH solution. Figure 5(b) shows that the extraction efficiency had no evident changes when the sample solution pH varied from 2 to 12. Since the pH values for the water, cucumber and tomato
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sample solutions were about 6.5, the pH of sample solution was not adjusted for the following experiments.
3.4.2.2 Effect of loading rate
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In SPE, the loading rate of the sample solution affects both the entire analysis time and the
recoveries of the analytes. To enable rapid and sensitive analysis, the loading rate was optimized. Figure 5(c) shows that there were no obvious changes in the peak areas of the five PUHs when the sample loading rate was changed from 1 mL min-1 to 10 mL min-1, illustrating that rapid adsorption kinetics exists between the adsorbent and the analytes. On the basis of the above results and to make the analysis time as short as possible, the sample loading rate was chosen at 10 mL min-1. 9
3.4.2.3 Effect of sample volume At a fixed concentration of the analytes, the adsorbed analytes in the SPE cartridge will gradually become saturated with increased sample volume. The sample volume at the saturation point is called the penetration volume. When the sample volume is above the penetration volume, the SPE recoveries will decrease. Therefore, different volumes of the sample solution (50, 100, 150, 200, 300 mL) were tested for the Ph-PPh3-KAP packed SPE cartridge. The results in Figure 5(d)
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show that there were no significant differences in the extraction efficiency of the analytes when the sample volume was increased from 50.0 mL to 300.0 mL, indicating that 300 mL has not yet reached its penetration volume. Considering that a large sample volume will require large amount
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of sample and long analysis time, 100.0 mL sample solution was chosen for the subsequent experiments.
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3.4.2.4 Effect of the type and volume of elution solvent
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In order to elute the adsorbed analytes as completely as possible, it is necessary to select an appropriate elution solvent and its volume. In this work, the three commonly used organic solvents
A
(methanol, acetonitrile and acetone) were tested as the elution solvent. Figure 5(e) shows that
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acetonitrile had the best desorption efficiency for all of the PUHs. Consequently, acetonitrile was chosen as the eluent. Then, the volume of acetonitrile was further optimized for a complete
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desorption of the PUHs. Figure 5(f) shows that the extraction recoveries were increased when the acetonitrile volume was increased from 0.3 to 1.0 mL, and remained almost unchanged when the eluent volume was changed from 1.0 to 1.2 mL, indicating that 1.0 mL acetonitrile was required for
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the complete elution of the PUHs. Thus, 1.0 mL of acetonitrile was selected in the subsequent experiments. Experimental results showed that after the used cartridge was further washed with 0.3
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mL acetonitrile, no carry-over was observed. Therefore, after the used cartridge was washed with 0.3 mL acetonitrile and 2 mL distilled water, it can be reused for the next extraction. The experimental results showed that the Ph-PPh3-KAP-packed SPE cartridge can be reused at least 30
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times without a significant decrease in extraction efficiency. 3.5 Adsorption capacity In order to explore the adsorption capacity of the Ph-PPh3-KAP, 100 mL aqueous solution spiked with each of the PUHs at three levels (0.040 µg mL-1, 2.0 µg mL-1 and 4.0 µg mL-1) was subjected to the SPE and analysis. The maximum adsorption capacity of the Ph-PPh3-KAP was 10
measured to be 16.6 mg g-1 for metoxuron, 16.1mg g-1 for monuron, 18.4 mg g-1 for chlorotoluron, 17.3 mg g-1 for monolinuron, and 24.2 mg g-1 for buturon, respectively. These values are bigger than those reported in the literature [38], suggesting that the Ph-PPh3-KAP has a strong adsorption capability for the PUHs. 3.6 Evaluation of the method
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Under the optimized conditions, the linear range, correlation coefficient (r), limits of detection (LODs, S/N=3), limits of quantitation (LOQs, S/N=9), and relative standard deviations (RSDs) of the method for the determination of the PUHs were investigated. For the elimination of the matrix
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effect, the matrix-matched calibrations were established by spiking the PUHs into the PUHs-free lake water, cucumber and tomato samples at different levels (0.1, 0.5, 1.0, 5.0, 10.0, 20.0, 40.0, 100.0 ng mL-1 for lake water, and 0.5, 1.0, 5.0, 10.0, 20.0, 40.0, 100.0 ng g-1 for cucumber and tomato samples). The results are shown in Table 1. For the lake water sample, a good linearity for
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metoxuron (r = 0.9999) was obtained in the range of 0.5-100 ng mL-1, and the LODs (S/N = 3) was
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0.02 ng mL-1 with the RSD at about 3.4%. The other four analytes had a good linearity (r> 0.9997)
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in the range of 0.1-100 ng mL-1 with the LODs between 0.01 and 0.02 ng mL-1 and the RSDs between 3.3 and 3.8%. For the tomato and the cucumber samples, the analytes gave a good linear
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response in the range of 0.5-100.0 ng g-1 with r between 0.9973 and 0.9999. The LODs were in the range of 0.03-0.05 ng g-1 for tomato and cucumber samples. The RSDs obtained by determining the
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PUHs-spiked samples at 5.0 ng g-1 were 4.0-6.1% for tomato sample and 4.8-6.0% for cucumber sample, indicating a good repeatability of the method.
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3.7 Analysis of real samples
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In order to study the practical applicability of the method, the residues of the PUHs in lake water, cucumber and tomato samples were analyzed by the current method, and the results are summarized in Table 2. As shown in Table 2, chlortoluron was found at about 0.15 ng g-1 in the tomato sample and metoxuron was detected at a concentration lower than its LOQ in the cucumber
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sample. Since no relevant reference sample is available for the validation of the method, spiked samples were prepared for recovery studies to check the accuracy of the method. The lake water was spiked with the analytes at three fortification levels of 0.5, 1.0, 10.0 ng mL-1 and the cucumber and tomato samples were spiked with the analytes at 0.5, 5.0 and 20.0 ng g-1, respectively. Then the spiked samples were analyzed by the developed method. The measured recoveries for the five PUHs ranged from 80.8% to 118% with RSDs between 2.9% and 11.5%, indicating that the method 11
has a quite good accuracy and precision. Figure 6 shows the chromatograms of the tomato and the cucumber samples with and without the analytes being spiked. 3.8 Comparison with literature methods The current method was compared with other reported methods [38-42] in the respect of the adsorbent material used, samples, linear range, LODs and RSDs. The comparison results in Table
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S2 show that the current method had comparable or lower LODs, and a better repeatability than other methods. In addition, the Ph-PPh3-KAP demonstrated rapid adsorption/desorption kinetics and large adsorption capacity toward the PUHs. However, in the preparation of the Ph-PPh3-KAP,
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after the reaction catalyzed by FeCl3, a time-consuming washing through Soxhlet extraction was needed to remove the catalysts, byproducts and unreacted monomers. 4 Conclusions
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In this work, a triphenylphosphine-based knitting aryl network polymer, Ph-PPh3-KAP, was
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investigated as the SPE adsorbent for the first time. It showed an excellent adsorption capability
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towards a variety of benzene ring-containing compounds. The possible adsorption mechanism was attributed to both hydrogen bonding and polar interactions between the Ph-PPh3-KAP and analytes.
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The Ph-PPh3-KAP was successfully applied to extract the PUHs residues from real samples with a satisfactory result. The current work indicates that the Ph-PPh3-KAP has a great application
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Acknowledgments
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potential as the SPE adsorbent for other applications.
Financial supports from the National Natural Science Foundation of China (31471643,
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31571925, 31671930), the Natural Science Foundation of Hebei Province (B2016204136, B2016204146, B2017204025), the Advance Program for the Introduction of Overseas Scholars by Hebei Province (CL201713), the Hebei “Double First Class Discipline” Construction Foundation for the Discipline of Food Science and Engineering of Hebei Agricultural University
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(2016SPGCA18), the Scientific and Technological Research Foundation of the Department of Education of Hebei Province (ZD2016085) and the Natural Science Foundation of Hebei Agricultural
University
(LG201607
LG201610,
acknowledged. References 12
ZD201703,
LG201712)
are
gratefully
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[37] T. Backhaus, M. Faust, M. Scholze, P. Gramatica, M. Vighi, L.H. Grimme, Joint algal toxicity
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of phenylurea herbicides is equally predictable by concentration addition and independent action, Environ Toxicol Chem. 23(2) (2004) 258-264. [38] X. Liang, J. Wang, Q. Wu, C. Wang, Z. Wang, Use of a hypercrosslinked triphenylamine polymer as an efficient adsorbent for the enrichment of phenylurea herbicides, J Chromatogr A. 1538 (2018) 1-7.
15
[39] S. Gao, J. You, X. Zheng, Y. Wang, R. Ren, R. Zhang, Y. Bai, H. Zhang, Determination of phenylurea and triazine herbicides in milk by microwave assisted ionic liquid microextraction high-performance liquid chromatography, Talanta 82(4) (2010) 1371-1377. [40] Y. Hu, Simultaneous determination of phenylurea herbicides in yam by capillary electrophoresis with electrochemiluminescence detection, J Chromatogr B. s 986-987 (2015) 143-148. [41] X. Dong, S. Liang, Z. Shi, H. Sun, Development of multi-residue analysis of herbicides in
IP T
cereal grain by ultra-performance liquid chromatography-electrospray ionization-mass spectrometry, Food Chem. 192 (2016) 432-440.
SC R
[42] S.L. Lin, Y.R. Wu, M.R. Fuh, Polymer monolith microextraction using poly(butyl methacrylate- co -1,6-hexanediol ethoxylate diacrylate) monolithic sorbent for determination of
A
CC E
PT
ED
M
A
N
U
phenylurea herbicides in water samples, Talanta. 147 (2016) 199-206.
16
Figure Captions Figure 1 Scheme for the synthesis of the Ph-PPh3-KAP. Figure 2 The FT-IR spectrum (a), the nitrogen adsorption-desorption isotherms and pore size
IP T
distribution curve (b), the SEM image (c), and the TG graph (d) for the Ph-PPh3-KAP. Figure 3 Dye color changes by the adsorption of the Ph-PPh3-KAP. (a) acid fuchsin; (b) acid orange 74; (c) congo red; (d) malachite green. For each dye, three different vials represent the dye
SC R
solution (left), dye solution with the adsorbent (middle) and the dye solution after the removal of the adsorbent (right).
Figure 4 The pseudo-second-order kinetics of the acid orange 74 by the Ph-PPh3-KAP (a) and the
U
adsorption equilibrium curve (b).
N
Figure 5 Comparison of different adsorbents (a); the effect of the sample solution pH (b), sample
A
loading rate (c), sample volume (d), the eluent type (e) and the eluent volum (f).
M
Figure 6 (a) The typical chromatograms of cucumber sample (bottom) and the cucumber sample spiked with the PUHs at each concentration of 0.5 ng g-1 (top); (b) the tomato sample (bottom) and
ED
the tomato sample spiked with the PUHs at each concentration of 0.5 ng g-1 (top). Peak identification: 1. Metoxuron; 2. Monuron; 3. Chlortoluron; 4. monolinuron; 5. Buturon. Mobile phase: acetonitrile-water (36:64 v/v) for (a), acetonitrile-water (40:60 v/v) for (b). Detection
A
CC E
PT
wavelength: 244 nm.
17
+
PPh3
FDA
Ph-PPh3-KAP
Scheme for the synthesis of the Ph-PPh3-KAP.
A
CC E
PT
ED
M
A
N
U
SC R
Figure 1
+
IP T
Ph
18
400
0.80
300
0.60
4000
O-H
)
0
0 3000
2000
-1
Wavenumber (cm
1000
0.0
0.2
)
100
0.6
0.8
1.0
Relative pressure (P/P0)
D
350oC
U
80 60
N
Weight Loss (%)
0.4
10 20 30 40 50 Pore width (nm)
SC R
0.55
100
0.12 0.10 0.08 0.06 0.04 0.02 0.00
IP T
P-CH2
3
1437
0.65
200
(
C-H
C-H
dv/dw cm /g nm
C-H
0.70
3
0.75
N2 adsorbed (cm /g)
Transmittance (a.u.)
0.85
40
M
A
20 0
0
100
200
300
400
500 o
Temperature ( C)
600
700
ED
Figure 2 The FT-IR spectrum (a), the nitrogen adsorption-desorption isotherms and pore size
A
CC E
PT
distribution curve (b), the SEM image (c), and the TG graph (d) for the Ph-PPh3-KAP.
19
IP T
Figure 3 Dye color changes by the adsorption of the Ph-PPh3-KAP. (a) acid fuchsin; (b) acid
SC R
orange 74; (c) congo red; (d) malachite green. For each dye, three different vials represent the dye solution (left), dye solution with the adsorbent (middle) and the dye solution after the removal of
A
CC E
PT
ED
M
A
N
U
the adsorbent (right).
20
100
0.24 0.16 0.08 0.00
0
5
10
15
Time (min)
20
25
30
80 60 40 20 0
0
5
10
15
Time (min)
20
25
30
IP T
-1
t/qt(min g mg )
Removal rate(%)
0.32
Figure 4 The pseudo-second-order kinetics of the acid orange 74 by the Ph-PPh3-KAP (a) and the
A
CC E
PT
ED
M
A
N
U
SC R
adsorption equilibrium curve (b).
21
(b)
Peak area(1.010 )
7 5
5
Peak area (1.010 )
4
8
(a)
3 2 1 0
6 5 Metoxuron Monuron Chlortoluron Monolinuron Buturon
4 3 2
KAP
C18
GCB
MWNTs
2
PS
4
6
8
(c)
100
pH
8
10
(d)
7
4 3
1 methanol
150
0.6
0.8
100
200
300
N 100
5
2
50
Sample volume (mL)
M
5
(e)
6
0
0
1 5 10 -1 8 Sample solution flow rate (mL min )
U
7
40
(f)
A
8
60
20
acetonitrile
Recovery(%)
2
SC R
Metoxuron Monuron Chlortoluron Monolinuron Buturon
4 3
Peak area (1.010 )
Recovery(%)
5
ED
Peak area10
5
80 6
12
IP T
Comparison of different adsorbents
80 60 40 20 0
acetone
0.3
1.0
1.2
The volum of eluent (mL)
CC E
PT
The type of eluent
Figure 5 Comparison of different adsorbents (a); the effect of the sample solution pH (b), sample
A
loading rate (c), sample volume (d), the eluent type (e) and the eluent volum (f).
22
b
IP T
a
SC R
Figure 6 (a) The typical chromatograms of cucumber sample (bottom) and the cucumber sample spiked with the PUHs at each concentration of 0.5 ng g-1 (top); (b) the tomato sample (bottom) and the tomato sample spiked with the PUHs at each concentration of 0.5 ng g-1 (top). Peak
U
identification: 1. Metoxuron; 2. Monuron; 3. Chlortoluron; 4. monolinuron; 5. Buturon. Mobile
N
phase: acetonitrile-water (36:64 v/v) for (a), acetonitrile-water (40:60 v/v) for (b). Detection
A
CC E
PT
ED
M
A
wavelength: 244 nm.
23
Table
Table 1 The linear range (LR), correlation coefficients (r), limits of detection (LODs), limits of quantitation (LOQs) and relative standard deviations (RSDs) for lake water, cucumber and tomato samples.
Cucumber
Metoxuron
0.1-100.0
0.9999
3.4
0.02
Monuron
0.1-100.0
0.9999
3.6
0.02
Chlortoluron
0.1-100.0
0.9999
3.8
Monolinuron
0.1-100.0
0.9998
3.3
Buturon
0.1-100.0
0.9997
3.7
Metoxuron
0.5-100.0
0.9993
4.0
Monuron
0.5-100.0
0.9996
5.7
Chlortoluron
0.5-100.0
0.9989
6.0
Monolinuron
0.5-100.0
0.9988
Buturon
0.5-100.0
0.9994
Metoxuron
0.5-100.0
Monuron
0.5-100.0
Chlortoluron Monolinuron Buturon
LOQs (ng mL-1 or ng g-1)
IP T
LODs (ng mL-1 or ng g-1)
SC R
RSD (%) (n = 5)
0.06 0.06 0.03
0.02
0.06
0.02
0.06
0.05
0.15
0.05
0.15
0.03
0.09
5.6
0.05
0.15
6.1
0.05
0.15
0.9995
6.0
0.05
0.15
0.9989
4.8
0.05
0.15
0.5-100.0
0.9992
5.9
0.03
0.09
0.5-100.0
0.9973
5.0
0.05
0.15
N
U
0.01
A
Tomato
r
M
Lake water
LR (ng mL-1 or ng g-1)
Analytes
ED
Samplesa
0.5-100.0 0.9997 5.0 0.05 0.15 -1 a For lake water sample, the unit of the LR, LOD and LOQ for the analytes is ng mL ; for tomato and cucumber
A
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PT
samples, the unit of the LR, LOD and LOQ for the analytes is ng g-1.
24
Table 2 Analytical results for the determination of the PUHs in lake water, cucumber and tomato samples.
Found (ng g-1)
0.0
ndb
0.5
0.53
106
1.0
0.92
10.0
9.88
0.0
nd
0.5
0.44
87.4
1.0
0.97
10.0
10.2
0.0
nd
0.5
0.44
87.3
9.10
0.5
1.0
1.18
118
3.99
5.0
10.0
10.2
102
3.01
0.0
nd
0.5
0.51
101
1.0
0.81
10.0
9.91
0.0
nd
0.5
0.46
91.6
1.01
101
R (%)
RSDs (%)
0.0
nd
10.0
0.5
0.46
92.9
9.14
91.6
4.86
5.0
5.43
109
3.95
98.8
3.43
20.0
20.0
100
4.05
0.0
nd
5.82
0.5
0.40
97.1
4.49
5.0
5.30
102
2.90
20.0
19.9
0.0
~0.15
Found (ng g-1)
R (%)
RS Ds (%)
IP T
RSDs (%)
0.41
81.9
5.36
5.38
108
6.00
20.0
99.8
4.05
nd
80.8
11.0
0.43
86.7
9.5
106
5.74
5.54
111
4.78
99.4
3.86
19.8
98.8
4.22
nd 11.5
0.51
101
4.47
5.53
111
6.00
5.32
106
5.92
20.0
19.8
99.1
4.16
20.2
101
3.51
0.0
nd
6.75
0.5
0.49
97.8
5.34
0.45
90.9
5.92
80.9
3.83
5.0
5.42
108
5.59
5.35
107
5.04
99.1
3.20
20.0
19.8
98.8
4.24
19.5
97.7
3.67
0.0
nd
11.3
0.5
0.49
98.4
5.12
0.55
110
6.21
6.21
5.0
5.28
106
6.05
5.11
102
4.96
10.0 10.0 100 3.88 Ra: recovery of the method; ndb: not detected.
20.0
19.8
99.2
3.84
19.7
98.3
4.05
Buturon
A
CC E
1.0
PT
Monolinuron
A
98.9
ED
0.49
M
Chlortoluron
Ra (%)
SC R
Monuron
Found (ng mL-1)
Cucumber sample (n = 5)
Spiked (ng g-1)
U
Metoxuron
Spiked (ng mL-1)
Tomato sample (n = 5)
N
Analytes
Water sample (n = 5)
25
nd
nd