Synthesis of carboxyl functionalized microporous organic network for solid phase extraction coupled with high-performance liquid chromatography for the determination of phenols in water samples

Journal Pre-proof Synthesis of carboxyl functionalized microporous organic network for solid phase extraction coupled with high-performance liquid chromatography for the determination of phenols in water samples Xue Li, Yuan-Yuan Cui, Cheng-Xiong Yang, Xiu-Ping Yan PII:

S0039-9140(19)31067-7

DOI:

https://doi.org/10.1016/j.talanta.2019.120434

Reference:

TAL 120434

To appear in:

Talanta

Received Date: 16 July 2019 Revised Date:

20 September 2019

Accepted Date: 3 October 2019

Please cite this article as: X. Li, Y.-Y. Cui, C.-X. Yang, X.-P. Yan, Synthesis of carboxyl functionalized microporous organic network for solid phase extraction coupled with high-performance liquid chromatography for the determination of phenols in water samples, Talanta (2019), doi: https:// doi.org/10.1016/j.talanta.2019.120434. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier B.V.

Graphical Abstract Carboxyl functionalized microporous organic network was facile synthesized as efficient adsorbent to fabricate solid phase extraction column for the efficient extraction of phenols from water.

Synthesis of carboxyl functionalized microporous organic network

for

solid

high-performance

phase liquid

extraction

coupled

chromatography

for

with the

determination of phenols in water samples Xue Li,b Yuan-Yuan Cui,a Cheng-Xiong Yanga* and Xiu-Ping Yanc

a

College of Chemistry, Research Center for Analytical Sciences, Tianjin Key

Laboratory of Molecular Recognition and Biosensing, Nankai University, Tianjin 300071, China b

School of Pharmaceutical Science and Technology, Tianjin University, 300072,

China c

State Key Laboratory of Food Science and Technology, International Joint

Laboratory on Food Safety, Institute of Analytical Food Safety, School of Food Science and Technology, Jiangnan University, Wuxi 214122, China

*Corresponding author. E-mail: [email protected]

1

Abstract: In this work, the carboxyl functionalized microporous organic network (MON-COOH) was synthesized as an efficient adsorbent to fabricate solid phase extraction (SPE) column for the extraction of p-nitrophenol, p-chlorophenol, 2,6-dichlorophenol and 2,3-dichlorophenol from water samples, followed by their analysis with high performance liquid chromatography (HPLC). The obtained MON-COOH was characterized with solid

13

C nuclear magnetic resonance

spectroscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, N2 adsorption-desorption isotherms, scanning electron microscope and water contact angle experiments. The integrating of carboxyl groups into aromatic MON’s networks led to their good enrichment for the studied phenols. The hydrogen binding, π-π and hydrophobic interactions played key roles during the extraction. Effects of adsorbents type, desorption solvent and volume, pH and ionic strength were studied. Under the optimal extraction conditions, the MON-COOH column for SPE coupled with HPLC for the determination of the selected four phenols gave the linear range of 0.5-1000 µg L-1, the limit of detections (LODs, S/N=3) of 0.13-0.62 µg L-1, the limit of quantifications (LOQs, S/N=10) of 0.43-2.06 µg L-1, the enhancement factors of 113-216, and the intra-day, inter-day and column-to-column precisions (relative standard deviations, RSDs) of 2.8-6.1, 4.1-8.7 and 6.7-10.3%, respectively. The developed method was successfully applied to the analysis of phenols in wastewater samples with the recoveries of 80.3-99.5%. These results revealed the potential of functional MONs as efficient adsorbents in sample pretreatment. KEYWORDS: microporous organic network, solid phase extraction, phenols, 2

sample pretreatment, high-performance liquid chromatography

3

1. Introduction Phenols are a class of hazardous organic pollutant existed extensively in the environment [1]. The phenols in the environment mainly come from human activities of agricultural and industrial production including pharmaceuticals, pesticides, dyes and paper [2]. Because of their toxicity and many side effects, phenols have been listed as the priority pollutants by the US Environmental Protection Agency (EPA) [3]. In addition, the European Union (EU) has classified several phenols as priority contaminants and set the limit of maximum total phenols concentration of 0.5 µg L-1 and individual concentration of 0.1 µg L-1 in drinking water [4]. Therefore, exploring accurate and reliable methods for the determination of phenols in water samples are of great importance and challenge. However, direct determination of phenols in water and environment is usually difficult due to their complex matrix interference and low concentration of phenols [5]. Proper sample pretreatment strategies are required before the quantitative analysis of phenols [6-13]. Many sample pretreatment techniques such as solid phase extraction (SPE) [6-9], solid phase microextraction (SPME) [10-12], and liquid-liquid extraction (LLE) [13] have been explored for the pretreatment and enrichment of phenols. SPE is the most widely used sample pretreatment technique for phenols because of its simple operation and less organic solvents consumption [6-9]. Phenols contain hydroxyl groups bonded directly onto benzene ring. The π-π, hydrophobic and hydrogen bonding interaction are the main adsorption/extraction mechanisms for phenols. Compared to the mature and complete analytical methods for non-polar or 4

weak polar compounds, the enrichment and analysis of polar targets from water samples are more difficult [14]. Because of the high water-solubility and polarity of phenols, traditional sample pretreatment methods show relatively low extraction efficiencies and recoveries [5]. The adsorbent is the core of SPE. Development of highly efficient and selective adsorbents for polar phenols is quite important and challenging in SPE. Until now, many kinds of advanced adsorbents including multi-walled carbon nanotubes [5], ionic liquid [15], cyclodextrin polymer [16], graphene oxide [12], octadecylsilica [17] and covalent organic frameworks [7,10] have been explored for SPE of phenols. Microporous organic networks (MONs) are a novel class of microporous materials with the merits of large surface area, good thermal and solvent stabilities, and easy modification [18-25]. MONs and MONs’ composites such as MIL-101@MON [26], Co@C [27], and UiO-66@MON [28] with aromatic and hydrophobic networks have been used as efficient adsorbents for the adsorption and extraction of harmful pollutants including toluene, polycyclic aromatic hydrocarbons, and 4-nitrobenzene, et al. However, these works are performed on MONs and MONs’ composites rely only on their good π-π and hydrophobic interactions between MONs and targets [29]. Incorporation of hydrogen bonding sites into MONs’ networks may largely promote their adsorption/extraction performance for phenolic compounds [30,31]. To elucidate this hypothesis and to further expend the potential of functionalized MONs in sample pretreatment, here we report the facile synthesis of carboxyl 5

functionalized MONs (MON-COOH) to fabricate their SPE columns for efficient enrichment of four typical phenols p-nitrophenol, p-chlorophenol, 2,6-dichlorophenol and 2,3-dichlorophenol from wastewater samples, followed by their analysis with high-performance liquid chromatography (HPLC). Chlorophenols are widely distributed in the environment as a result of the degradation of pesticide and chlorination of drinking water [32]. Widespread consumption and illegal discharge of chlorophenols in water have led to a major source of water pollution and caused a great threat to aquatic life and human health due to their potential carcinogenic and mutagenic effects [33]. Nitrophenols are formed photochemically in the atmosphere from vehicle exhausts [34]. Therefore, nitrophenols and chlorophenols are selected as the model phenols in this work. With the aid of predesigned hydrogen bonding, π-π and hydrophobic interaction sites in MON-COOH’s networks, the MON-COOH shows good enrichment for phenols. The experimental parameters such as pH, ionic strength, desorption solvent and volume those affecting the SPE of phenols are investigated. The developed method gives good linearity, low limits of detection and large enrichment factors for the studied phenols. Determination of phenols in wastewater samples is also realized. These results reveal the potential of MON-COOH as efficient adsorbent in SPE of phenols and the promise of functionalized MONs in sample pretreatment. 2. Experimental 2.1. Reagents and materials All reagents are at least of analytical grade. p-Nitrophenol (4-NP), 6

p-chlorophenol (4-CP), 2,6-dichlorophenol (2,6-DCP) and 2,3-dichlorophenol (2,3-DCP), 2,5-dibromobenzoic acid, 1,4-dibromobenzene, 2,5-dibromophenol, copper (I) iodide and triethylamine are purchased from Aladdin Chemistry Co., Ltd. (Shanghai, China). Tetrakis(4-ethynylphenyl)methane is bought from Chengdu Tongchuangyuan Pharmaceutical Technology Co. (Chengdu, China). Toluene is obtained

from

Chemical

Reagent

Sixth

Factory

(Tianjin,

China).

Bis(triphenylphosphine)palladium(II) chloride is purchased from Energy Chemical Co. Ltd. (Shanghai, China). Ultrapure water is supplied by Wahaha Foods Co. Ltd. (Tianjin, China). Methanol (HPLC grade), ethanol, acetonitrile and dichloromethane are obtained from Concord Technology (Tianjin, China). 2.2. Instrumentation The chromatographic system consists of a Waters 600 pump and a 2996 diode array detector (DAD). The HPLC analysis of phenols is performed on an Accurasil C18 column (4.6 mm i.d. × 15 cm long, Ameritech, USA) at a flow rate of 1.0 mL min-1 using methanol/water/formic acid 60/40/0.5 as the mobile phase under 280 nm. Thermogravimetric analysis (TGA) is performed on a PTC-10A thermal gravimetric analyzer

(Rigaku,

Japan)

from

room

temperature

to

700

o

C.

The

N2

adsorption-desorption experiments are recorded on a NOVA 2000e surface area and pore size analyzer (Quantachrome, USA) at 77 K. The scanning electron microscope (SEM) images are recorded on a Gemini SEM-500 scanning electron microscope (ZEISS, Germany). The water contact angle measurements are performed on an OCA150pro optical contact angle measuring device (Beijing Eastern-Dataphy, China). 7

The fourier transform infrared spectroscopy (FT-IR) were measured on a Nicolet IR AVATAR-360 spectrometer (Nicolet, USA). The solid 13C nuclear magnetic resonance (13C NMR) experiments were recorded on Infinityplus 300 (VARIAN, USA). 2.3. Synthesis of MON-COOH, MON and MON-OH The MON-COOH was simply synthesized via the solvent refluxing method (Fig. 1). Typically, copper (I) iodide (8.8 mg, 0.012 mmol) and bis(triphenylphosphine) palladium dichloride (33.6 mg, 0.012 mmol) were dispersed with triethylamine (30 mL) and toluene (30 mL) in a dried flask. The tetrakis(4-ethynylphenyl)methane (200.0 mg, 0.48 mmol) and 2,5-dibromobenzoic acid (268.7 mg, 0.96 mmol) was then added. The mixture was magnetic stirred and heated to reflux for 4 h to synthesize MON-COOH. The resulting precipitates were collected by centrifugation (10000 rpm, 5 min), thoroughly washed with dichloromethane and ethanol, and dried under vacuum at room temperature overnight. The MON and MON-OH were synthesized according to our reported works [29,31]. Copper (I) iodide (8.8 mg, 0.012 mmol) and bis(triphenylphosphine) palladium dichloride (33.6 mg, 0.012 mmol) were dissolved with triethylamine (30 mL) and toluene (30 mL). After the addition of tetrakis(4-ethynylphenyl)methane (200 mg, 0.48 mmol) and 1,4-dibromobenzene (226 mg, 0.96 mmol), the mixture was stirred (500 rpm) for 4 h at room temperature to synthesize MONs. The resulting precipitates were collected by centrifugation (10000 rpm, 5 min), washed with dichloromethane and absolute ethanol, and dried under vacuum at room temperature overnight. The MON-OH was synthesized under the same condition by changing the 8

1,4-dibromobenzene (226 mg, 0.96 mmol) to 2,5-dibromophenol (242 mg, 0.96 mmol). 2.4. Sample preparation The stock solutions of 4-NP, 4-CP, 2,3-DCP and 2,6-DCP (1 mg mL-1 for each) were prepared with methanol and stored at 4 oC in the dark. The working solution was prepared from the stock solution by stepwise dilution with ultrapure water. The river and lake water samples were collected from local lake and river (Tianjin, China). The water samples were filtered with 0.22 µm Millipore cellulose membrane immediately after sampling. 2.5. SPE procedures The SPE procedures were performed as follows. Typically, 50 mg of MON-COOH was loaded in a 6 mL empty SPE column (Thermo Scientific, USA) with both frits fixed. Before sample loading, the MON-COOH column was conditioned with 10 mL of ultrapure water. Then, 50 mL of the standard phenols solution or wastewater samples were passed though the MON-COOH column with the aid of a syringe rod. After that, the MON-COOH column was washed with 10 mL of ultrapure water to eliminate the nonspecific adsorbed phenols on MON-COOH. The adsorbed phenols were then desorbed from the MON-COOH column with 1.0 mL of methanol (0.5 mL × 2). The eluent was concentrated via N2 flow, diluted with methanol to 0.2 mL and sampled for HPLC analysis. The MON-COOH column was then reused for another SPE procedure. 3. Results and discussion 9

3.1. Characterization of MON-COOH The synthesized MON-COOH was characterized with solid

13

C NMR, FT-IR,

TGA, N2 adsorption-desorption isotherms, SEM and water contact angle experiments (Fig. 2). The chemical shifts of solid

13

C NMR at 120-150 and 70-90 ppm for

MON-4COOH corresponded to the signals of benzyl carbon, aromatic ring and internal alkyne (Fig. 2a) [29]. The chemical shift at 190 ppm was assigned to the characteristic peak of carboxyl groups. The FT-IR peak at 1700 cm-1 was the typical stretching vibration of carbonyl groups, revealing the successful synthesis of MON-COOH. The peaks at 2250 and 1500 cm-1 were ascribed to C≡C and C=C bonds vibration of MON-COOH (Fig. 2b). Compared with MON, the appearance of -OH and C=O peaks of carboxyl groups on MON-COOH confirmed the successful incorporation

of

carboxyl

groups

on

MON-COOH

(Fig.

2b).

The

N2

adsorption-desorption isotherms showed the BET surface area of the synthesized MON-COOH was 584 m2 g-1 (Fig. 2c). The TGA curve showed the MON-COOH was stable up to 300 oC (Fig. 2d). The SEM image showed the irregular spherical shaped of MON-COOH with the particle size of about 1 µm (Fig. 2e). The water contact angle of the synthesized MON-COOH was 129o (Fig. 2f), which was lower than pure MONs without modification (142o) [29], further revealing the successful synthesis of MON-COOH and the incorporation of carbonyl groups could lead to the improvement of the hydrophilicity of MONs. 3.2. Effect of pH The pH of the solution was an important factor affecting the SPE efficiency. The 10

pH could influence the dissociation of phenols in aqueous solution and then further affect the extraction efficiency of phenols on adsorbents. Therefore, effect of pH on SPE of 4-NP, 4-CP, 2,6-DCP and 2,3-DCP on MON-COOH was investigated in the pH range of 3-11 (Fig. 3a). The results showed that the peak areas of 4-NP, 4-CP, 2,6-DCP and 2,3-DCP changed little in the pH range of 5-8, suggesting the stable extraction efficiency of MON-COOH for phenols in neutral and weakly acidic environments. However, the peak areas of 4-NP, 4-CP, 2,6-DCP and 2,3-DCP decreased as the pH values increased from 10 to 11, showing the alkaline condition was not favorable for SPE of these phenols on MON-COOH. The pKa values of 4-NP, 4-CP, 2,6-DCP and 2,3-DCP were 7.15, 9.38, 6.79 and 7.45, respectively. All the studied phenols should be exited as neutral or undissociated form when pH < 8, leading to the constant extraction efficiency on MON-COOH based on the good hydrogen bonding interaction between phenols and MON-COOH. When pH > 8, the 4-NP, 2,6-DCP and 2,3-DCP should be existed as dissociated form, which lead to the destruction of the hydrogen bonding interaction between phenols and MON-COOH, decreasing the extraction efficiency of 4-NP, 2,6-DCP and 2,3-DCP on MON-COOH. The large pKa value of 4-CP (9.38) resulted in the good extraction on MON-COOH even at pH = 10. These results revealed the important role of hydrogen bonding interaction between phenols and MON-COOH during the extraction. Considering that the pH values of the natural and wastewater samples investigated were about or less than 7, the pH of sample solution in this work was not adjusted. 3.3. Effect of ionic strength 11

Effect of ionic strength for SPE of 4-NP, 4-CP, 2,6-DCP and 2,3-DCP on MON-COOH was studied in the NaCl concentration range of 0-0.3 g mL-1 (Fig. 3b). The peak areas of 4-NP, 4-CP, 2,6-DCP and 2,3-DCP changed little as the concentration of NaCl increased from 0 to 0.15 g mL-1, showing the good anti-interference property of MON-COOH. In general, increase of the NaCl concentration may lead to the decrease of the phenols’ solubility in aqueous phase, which was favorable for their transformation or extraction on MON-COOH. However, the added NaCl could also increase the matrix effect and solution viscosity and then decrease the diffusion rate, which were negative for their transformation or extraction on MON-COOH. Further increase of the NaCl from 0.15 to 0.30 g mL-1 led to the decrease of the extraction efficiency for the studied phenols on MON-COOH. Therefore, no NaCl was added in subsequent experiments. 3.4. Effects of desorption solvent and volume Methanol, ethanol and acetonitrile were chosen as the desorption solvents to desorb 4-NP, 4-CP, 2,6-DCP and 2,3-DCP from MON-COOH (Fig. 3c). The results showed that the methanol gave the best desorption efficiency to the studied phenols. Effect of methanol volume on the desorption of 4-NP, 4-CP, 2,6-DCP and 2,3-DCP from MON-COOH was further studied (Fig. 3d). The results showed that 1.0 mL of methanol (0.5 mL × 2) was sufficient to desorb the adsorbed phenols from MON-COOH. 3.5. Method validation The figures of merits for the SPE using MON-COOH as the sorbent for HPLC 12

determination of phenols were summarized in Table 1. A series of standard phenols solutions (0.1-2500 µg L-1) were prepared to determine the linear range, limit of detection (LOD) and limit of quantification (LOQ) of the proposed method. The linear range of proposed method for the determination of 4-NP, 4-CP, 2,6-DCP and 2,3-DCP were 0.5-1000, 1.0-1000, 1.0-1000, and 2.5-1000 µg L-1, respectively. The precisions (RSDs, %) for intra-day (n = 7), inter-day (n = 5) and column-to-column (n = 3) were 2.8-6.1%, 4.1-8.7% and 6.7-10.3%, respectively. The LODs (S/N = 3) and LOQs (S/N = 10) for the studied phenols were in the range of 0.13-0.62 µg L-1 and 0.43-2.06 µg L-1, respectively. The MON-COOH also gave good enhancement factors (EFs, defined as the ratio of the sensitivity of an analyte after extraction to that before extraction) of 113-216 for the studied phenols and offered higher EFs than a carboxyl-ion-exchanger D113 acrylic resin (Table 2). Furthermore, the MON-COOH column could be used repeatedly without any decrease of the extraction efficiency. The MON-COOH column after 80 extraction cycles gave comparable efficiency for the studied four phenols to the fresh one (Fig. 4a), showing the good reusability of MON-COOH for phenols. Compared with other reported methods (Table 3), the developed MON-COOH SPE-HPLC method gave wider linear range, lower LODs and better reusability. 3.6. Adsorption mechanisms To evaluate the adsorption mechanisms of MON-COOH for phenols, SPE of the studied phenols on MONs and MON-OH were compared (Fig 4b). The MONs without any functional groups gave the lowest extraction efficiency for the studied 13

four phenols among MONs, MON-OH and MON-COOH loaded SPE column. Incorporation of hydrophilic -OH and -COOH groups (hydrogen bonding sites) into MONs’ networks lead to the largely improvement of their extraction efficiency for phenols, revealing the dominant role of hydrogen bonding interaction between phenols and MON-COOH or MON-OH. However, the MONs still gave the EFs values of 60-105 for these four phenols (Table 2), suggesting the hydrogen bonding interaction should not be the only extraction mechanism during the SPE procedure in this work. The π-π and hydrophobic interactions between aromatic phenols and hydrophobic MON-COOH’ networks could also play important roles in this study. 3.7. Selectivity and ion-exchange capacity study The selectivity and ion-exchange capacity of MON-COOH for cations and anions in lake and river water samples were studied (Tables S1 and S2). The concentration of Na+ in lake and river water samples were decreased after the adsorption on MON-COOH (Table S1), revealing the cation ion-exchange capacity of MON-COOH and its good selectivity for Na+. The slight decrease of the concentration for Cl-, NO2- and SO42- in lake and river water samples after adsorption on MON-COOH also showed the potential of MON-COOH to the elimination or enrichment of these anions from waste water samples (Table S2). The cation ion-exchange property of MON-COOH was then evaluated by performing the NaCl effect on pH in MON-COOH suspension (Fig. S1). The pH of MON-COOH suspension was slightly decreased and then leveled off as the increase of NaCl in MON-COOH suspension, confirming the cation ion-exchange property of 14

MON-COOH. The exchanged H+ from the MON-COOH by Na+ led to the decrease of the pH value. 3.8. Real sample analysis To evaluate the practical applicability of the established SPE-HPLC method, the determination of these phenols in lake and river water samples were performed (Fig. 5, Table 4). The studied four phenols were not detected when the volume of the concentrated local lake and river water samples was 50 mL. Further increase of their volume to 1.5 L, the 4-NP was detected with the concentration of 0.028 and 0.032 µg L-1 for the studied lake and river water samples, respectively. The recoveries of phenols in two spiked levels (10 and 25 µg L-1) were in the range of 80.3-99.5%. To better understand the cause of analyte-loss of the proposed method for phenols, effluents from 50 mL river and lake water samples and 10 mL of ultrapure water passed through the MON-COOH column were concentrated and analyzed (Fig. 5). The results showed that small amount of analytes were detected in the effluents from the MON-COOH filtrated river and lake water samples. The analyte-loss likely resulted from the uneven packing of MON-COOH for the studied phenols, which lead to the low recoveries for phenols. 4. Conclusion In summary, we have reported the facile synthesis of carboxyl functionalized MON-COOH to fabricate robust SPE column for the enrichment and determination of phenols in wastewater samples. Relying on the pre-designed hydrogen bonding, π-π and hydrophobic interaction sites in networks, the synthesized MON-COOH gave 15

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Figure captions Fig. 1. Illustration for the synthesis of MON-COOH. Fig. 2. (a) Solid 13C NMR spectrum, (b) FT-IR spectrum, (c) N2 adsorption desorption isotherms, (d) TGA curve, (e) SEM and (f) the water contact angle of the synthesized MON-COOH. Fig. 3. Effects of (a) pH, (b) ionic strength, (c) desorption solvent and (d) methanol volume on the SPE of phenols on MON-COOH packed SPE column. The spiked concentrations of the studied phenols were 100 µg L-1 for each. Error bars showed the standard deviations for three replicate extractions. Fig. 4. (a) Extraction cycles of MON-COOH for phenols. (b) Extraction of phenols on MONs, MON-OH and MON-COOH. The concentrations of each phenol are 100 µg L-1. Error bars show the standard deviations for three replicate extractions. Fig. 5. HPLC chromatograms of (a) lake and (b) river water samples. The concentrations of spiked phenols are 1, 0 µg L-1; 4, 10 µg L-1 and 5, 25 µg L-1, respectively. 2, effluent from 10 mL of ultrapure water passed through the MON-COOH column; 3, effluent from 50 mL of waste water sample passed through the MON-COOH column; 6, SPE of 1.5 L of waste water sample on MON-COOH column.

23

Table 1. Parameters of the proposed SPE-HPLC method for the determination of phenols.

a

Phenols

Linear range (µg L-1)

R2

4-NP 4-CP 2,6-DCP 2,3-DCP

0.5-1000 1.0-1000 1.0-1000 2.5-1000

0.999 0.999 0.997 0.995

Precision (RSDs)a (%) Intra-day Inter-day Column to (n=7) (n=5) column (n=3) 3.4 6.5 7.1 2.8 4.1 6.7 4.7 6.4 8.8 6.1 8.7 10.3

the concentration of spiked phenols is 100 µg L-1.

LODs (µg L-1)

LOQs (µg L-1)

0.13 0.21 0.23 0.62

0.43 0.70 0.77 2.06

Table 2. EFs values of the proposed SPE-HPLC method for phenols using MON, MON-OH, MON@COOH and D113 acrylic resin as the adsorbents. Phenols 4-NP 4-CP 2,6-DCP 2,3-DCP

MON 98 ± 2 73 ± 3 60 ± 2 105 ± 4

EFs (means ± s, n=3) MON-OH MON-COOH D113 acrylic resin 185 ± 4 216 ± 6 24 ± 2 122 ± 5 135 ± 4 23 ± 1 103 ± 3 113 ± 3 25 ± 1 155 ± 3 184 ± 4 9±1

Table 3. Comparison of the developed method with other reported methods for the determination of phenols. Adsorbents Analytes Graphitized carbon 4-CP, 4-NP, 2,6-DCP a MIP 4-NP b c AmberliteXAD-2 SDVB /AC /C18 4-CP NH2-MWCNTd/PDMSe 4-NP f PDMS/CTF 4-NP Amberlite XAD-2 4-CP, 2,6-DCP C18 4-CP, 2,3-DCP, 2,6-DCP Amberlite XAD-2 4-CP, 2,3-DCP, 2,6-DCP MON-COOH 4-NP, 4-CP, 2,3-DCP, 2,6-DCP a MIP: molecularly imprinted polymer b SDVB: styrene-divinylbenzene c AC: activated carbon d MWCNT: multi-walled carbon nanotube e PDMS: polydimethylsiloxane f CTF: covalent triazine-based framework g SBSE: stir bar sorptive extraction

Methods SPE-GC-MS SPE-HPLC-UV SPE-GC-FID SBSEg-HPLC-UV SBSE-HPLC-UV SPE-GC-MS SPE-HPLC SPE-HPLC SPE-HPLC-PDA

Linear range (µg L-1) 1-50 6-1000 3-40 5-1000 0.5-500 1-160 0.5-1000

LODs (µg L-1) 0.03 0.3-0.5 1.5 1.18 0.17 0.4 5.9-9.8 4.6-6.0 0.13-0.62

Ref. [35] [36] [37] [5] [7] [8] [17] [17] This work

Table 4. Analytical results for the determination of phenols in river and lake water samples (n=3).

Phenols 4-NP

4-CP

2,6-DCP

2,3-DCP

a

not detected

−1

Recovery ± SD (%, n=3)

Spiked (µg L ) River water

Lake water

0

nda

nda

10

85.0 ± 1.1

88.7 ± 2.3

25

93.2 ± 0.8

92.5 ± 1.8

0

nda

nda

10

80.3 ± 1.3

82.9 ± 2.1

25

95.2 ± 1.7

99.5 ± 3.1

0

nda

nda

10

85.5 ± 0.9

90.1 ± 1.5

25

94.0 ± 2.4

94.2 ± 1.7

0

nda

nda

10

81.8 ± 0.7

81.3 ± 1.9

25

89.8 ± 1.6

84.2 ± 3.5

Highlights


MON-COOH was facile synthesized for efficient SPE of phenols.




MON-COOH gave low LODs and large EFs for phenols.




Hydrogen bonding, π-π and hydrophobic interaction dominate the good SPE of phenols.