Magnetic solid phase extraction of sulfonamides based on carboxylated magnetic graphene oxide nanoparticles in environmental waters

Accepted Manuscript Title: Magnetic solid phase extraction of sulfonamides based on carboxylated magnetic graphene oxide nanoparticles in environmental waters Authors: Shiqian Gao, Yutong Guo, Xinyue Li, Xuedong Wang, Junxia Wang, Feiyue Qian, Haidong Gu, Zhanen Zhang PII: DOI: Reference:

S0021-9673(18)31166-X https://doi.org/10.1016/j.chroma.2018.09.015 CHROMA 359680

To appear in:

Journal of Chromatography A

Received date: Revised date: Accepted date:

17-1-2018 1-9-2018 8-9-2018

Please cite this article as: Gao S, Guo Y, Li X, Wang X, Wang J, Qian F, Gu H, Zhang Z, Magnetic solid phase extraction of sulfonamides based on carboxylated magnetic graphene oxide nanoparticles in environmental waters, Journal of Chromatography A (2018), https://doi.org/10.1016/j.chroma.2018.09.015 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.

Magnetic solid phase extraction of sulfonamides based on carboxylated magnetic graphene oxide nanoparticles in

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environmental waters

Shiqian Gaoa,b*, Yutong Guoa, Xinyue Lia, Xuedong Wanga,b, Junxia

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Wanga,b, Feiyue Qiana,b, Haidong Gua,b, Zhanen Zhanga,b,c*

a

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College of Environmental Science and Engineering, Suzhou University of Science

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and Technology, No. 1 Kerui Road, Suzhou 215009, P.R. China b

Jiangsu Key Laboratory of Environmental Science and Engineering, Suzhou

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University of Science and Technology, No. 1 Kerui Road, Suzhou 215009, P.R. China c

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National and Local Joint Engineering Laboratory of Municipal Sewage Resource

*

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Utilization Technology, No. 1 Kerui Road, Suzhou 215009, P.R. China

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Corresponding author. Zhanen Zhang, Shiqian Gao

Tel.: +86-512-68093060; Fax: +86-512-68093060

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E-mail address: [email protected], [email protected]

Highlights

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The carboxylated magnetic graphene oxide nano-sorbent was synthetized.

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The distribution of -COOH and amount on the CMGO surface was determined.

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The CMGO-MSPE was developed for the concentration of amine-based



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organic pollutants.

The CMGO showed good extraction efficiency for sulfonamides from

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real-world waters.

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Abstract

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A magnetic nano-adsorbent material was prepared by functionalizing carboxylic

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group onto the granule surface of magnetic graphene oxide nanoparticles (CMGO), using in-situ co-precipitating method. The surface morphology was characterized by

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SEM and TEM. The CMGO was selected as the adsorbent for the magnetic solid phase extraction (MSPE) of sulfonamides (SAs) from environmental water samples,

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and the eluted analytes were determined by ultra high performance liquid chromatography-tandem

mass

spectrometry (UHPLC-MS/MS).

A series

of

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experimental parameters were optimized to improve the extraction efficiency such as amount of CMGO, extraction time, pH, ionic strength of the sample solution and desorption conditions. When the pH of water sample was 4.00, the extraction

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recoveries (ERs) for SAs were over 82.0 % with 15.0 mg CMGO adsorption for 20 min. Under the optimized extraction conditions, linear range was obtained with coefficients of determination (R2)≥0.9983. The limits of detection for this proposed method were in the range of 0.49-1.59 ng/L, and the enrichment factors were 1320-1702 for eight SAs. The newly developed method was successfully applied to the analysis of trace SAs in real-world water samples, which provided satisfactory

ERs in the range of 82.0-106.2% with RSDs less than 7.2%. Overall, it shows a great potential for the concentration of trace amine organic pollutions in complex matrices.

Key words: Carboxylated magnetic graphene oxide; Magnetic solid phase extraction;

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Sulfonamides; Environmental water samples

1. Introduction

Sulfonamide antibiotics (SAs) are a kind of broad-spectrum antibiotics, which were widely applied to inhibit bacterial protein synthesis in early stage and eliminate

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inflammation in clinical medicine and animal husbandry [1]. They pose a great concern to human health owing to their extensive usage and inability to be easily biodegraded in the environment [2]. Meanwhile, because the metabolism of SAs is

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incomplete, a large part of them is excreted through urine or feces, and thus can be

detected in wastewater, surface water and even ground water [3, 4]. It is reported that SAs are potentially toxic to the aquatic organisms and humans by drinking water and

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the food chain [5]. Bacterial dysbiosis caused by SAs residues in the human

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body leads to allergic sensitization and invasive growth of tumor cells through one or

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several mechanisms, which make SAs ineffective in the treatment of several diseases

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in the long term [6]. To protect the food security and improve the quality of water body, the MRLs of SAs in food and drinking water (10.0-100 μg·kg-1) are established

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by national authorities and by the Codex Alimentarius Commission of United Nations [7]. Therefore, it is imperative to develop new methods for the highly efficient

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extraction and determination of trace SAs in complex matrices. Several analytical methodologies have been developed and reported to

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determine SAs residues in water. These methods vary according to the different analytic matrices, including immunoassay [8], capillary electrophoresis [9], gas chromatography-mass (GC-MS) [10], high performance liquid chromatography

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(HPLC) [11] and ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) [12]. UHPLC-MS/MS has already gained popularity as an analytical platform for the screening of antibiotics due to the potency of tandem MS such as multi-analytical property, sensitivity, selectivity and possibility of characterizing compounds by molecular mass or formula.

One of the most important stages in the analysis of samples is the extraction and pre-concentration trace pollutants in complex environmental samples. Liquid liquid extraction (LLE) [13] and solid phase extraction (SPE) [14] are common methods used for the extraction of trace pollutants in complex matrix samples. Magnetic solid phase extraction (MSPE) technology has attracted extensive attention in recent years, particularly for the enrichment of trace organic pollutants in foods and environmental

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waters [15, 16]. Functionalized magnetic nanoparticles are dispersed into the solution, from which the target analytes are concentrated on the magnetic nanoparticles

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by bonding action [17]. The good dispersion was beneficial to enhance the contact surface area effectively between the adsorbent and analytes in the sample solution. The magnetic polymers were separated from sample matrices rapidly and

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conveniently by applying appropriate magnetic field, and then the target analystes are

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eluted using a small amount of organic solvent [18]. This method avoids the

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procedure of column-packing and provides a simple extraction model for the absorption and desorption of target analytes at atmospheric pressure [19].

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Graphene (G), an emerging carbon-based nanomaterial, possesses a single-layer

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or few-layer thickness of sp2-hybridized carbon atoms arranged in a honeycomb pattern [20]. Graphene oxide (GO) is a kind of hexagonal rings-based carbon network, which has a large delocalized π-electronic system and high specific surface area. GO

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can be enriched with oxygen-containing functional groups in the form of hydroxyl (-OH) and epoxide (C-O) groups on the basal plane, and carbonyl (C=O) and

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carboxyl (-COOH) groups positioned at the edges [21]. The existence of π-conjugated structure endows GO with a strong affinity for benzenoid structures [22]. Nowadays, functionalized G and GO nanomaterials have been widely investigated due to their

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remarkable properties and unique structures [23]. The photoelectric properties and water solubility of GO are improved by carboxylation [24]. The deoxygenation of GO can undergo fast in strongly alkaline solutions, which is helpful to increase the rate of nucleophilic substitution reaction between epoxy and hydroxyl groups. The carboxylation of GO sheets will effectively enhance the extraction selectivity of GO for SAs, because of the non-covalent forces between GO and some groups of SAs

molecular structures, such as -NH2 or -SO2NH- and aniline groups [25]. The non-covalent forces mentioned above contain electrostatic forces, hydrogen bonding, stacking and hydrophobic effect [26]. The layers of carboxylated GO (CGO) tends to aggregate in aqueous solution, which lending to the reduction of surface area and adsorption capability. Furthermore, CGO is ultralight and water soluble that it is tough to retrieve from a suspension [27].

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The pretreatment process will be time-consuming when large volume samples are

processed [28]. The magnetic core can be introduced into CGO dispersion process,

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which has advantages of high breakthrough volume and easy elution of analytes. Meanwhile, the phenomenon of CGO aggregation in aqueous solution is prevented.

In this work, the carboxylated magnetic graphene oxide (CMGO) was used as a

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sorbent to extract trace SAs in environmental waters prior to UHPLC-MS/MS

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detection. After the extraction, the adsorbent can be conveniently washed using

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methanol and ultrapure water. As a consequence, this proposed method has great potential application value in preconcentration of trace organic contaminants in

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environmental waters because of its fast, simple, green and accurate characteristics for

2. Experimental

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the determination of SAs in real-world waters.

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2.1. Chemicals and reagents

Eight sulfonamides (SAs) standards with purities of >98.0% were purchased from

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Sigma-Aldrich (St. Louis, MO, USA): sulfachloropyridazine (SCP), sulfaquinoxaline (SQX), sulfadiazine (SDZ), sulfamerazine (SMR), sulfamethoxazole (SMZ), sulfapyridine (SPD), sulfathiazole (STZ) and sulfamonomethoxine (SMT). The stock

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solutions of 500.0 μg/mL for individual SAs were prepared in a mixture of HPLC-grade methanol-0.1% formic acid. The mixed standard stock solutions (1.0 μg/mL) containing eight SAs were obtained by dissolving 20 μL of each compound in 10.0 mL methanol-0.1% formic acid. Three environmental water samples, collected from the outlet of one sewage plant and aquaculture water (1# and 2#), Suzhou, China, which were filtered through a 0.45 μm filter membrane immediately after being

sampled and then stored at 4℃. The spiked samples containing SAs were prepared by spiking the 20.0 μL of working solutions into environmental water samples and stored at 4 ℃ for analysis within one week. Graphene oxide powder (99%, single-layer rate ≥96%) was purchased from Leadernano Technology Co., Ltd. (Jining, China). HPLC-grade methanol, acetonitrile, acetone and ethyl acetate were obtained from Tedia Company Inc. (Fairfield, USA).

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FeCl3·6H2O, FeSO4·7H2O, NaOH, NH3·H2O and alcohol were supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Chloroacetic acid was

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procured from Shanghai Anpel Experimental Technology Co., Ltd. (Shanghai, China).

All other chemicals used in the experiment were of analytical grade unless otherwise stated. Ultrapure water was prepared with Milli-Q purification system.

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2.2. Apparatus and instruments

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LC-tandem MS analyses were carried out in a system consisting of an Ultimate

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3000 UHPLC system (Thermo Scientific, San Jose, CA, USA) coupled to a triple-quadrupole tandem mass spectrometer (TSQ Quantum Ultra AM, Finnigan,

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USA). Identification and quantification were achieved by electro-spray ionization (ESI) in positive mode using multiple reaction monitoring (MRM). The separation

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was performed using a Zorbax Eclipse XDB-C18 column (3.0 mm×50 mm i.d., 1.8 μm) at 30℃. The mobile phase consisted of a mixed solution containing 0.1% formic acid

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(A) and methanol (B) and the flow rate was set at 0.3 mL/min. Linear gradient elution was performed as follows: 0-1 min, 10-40% B; 1-4 min, 40% B; 4-4.2 min, 40-60% B;

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4.2-6 min, 60% B; 6-6.5 min, 60-10% B; 6.5-9 min, 10% B. The injection volume was 10.0 μL. The capillary voltage was 3500 V and capillary temperature was 350℃. Argon was used as the collision gas, with shealth gas pressure and auxiliary gas

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pressure at 20 MPa and 5 MPa, respectively. The mass spectrometric information regarding eight SAs is listed in Table S1. The infrared spectra analysis of the magnetic adsorbent was performed using a Nicolet-6700 Fourier transform infrared (FT-IR) spectrometer (Thermo Scientific, San Jose, CA, USA) in the form of KBr pellets. The Milli-Q water purification system (Millipore, Bedford, MA, USA), DC-12 pressure blowing concentrator (Shanghai Anpel Experimental Technology Co., Ltd., China),

HY-2 shaker (Suzhou Weier Experimental Equipment Co., Ltd., China), SK-1 vortex and JJ-1 electric stirrer (Jintan Kexi Instrument Co., Ltd., China) were used in the experiment. 2.3. Synthesis of CMGO An aliquot of GO (1.0 g) was introduced into 200.0 mL of water by ultrasonic vibration to obtain a homogeneous suspension. Then, 6.0 g of NaOH and 5.0 g of

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chloroacetic acid were added to GO solution, and the mixture was continuously ultrasonicated at 25℃ for 3 h to generate the carboxylic groups on the surface of GO

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via the carboxylation of epoxy and hydroxyl groups. The solid product was collected

by centrifugation and washed with ultrapure water and alcohol [27]. Finally, the CGO suspension was obtained and dispersed in 200 mL of water. 2.71 g of FeCl3·6H2O and

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1.67 g of FeSO4·7H2O were dissolved into the above CGO suspension. The pH value

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of the mixture was adjusted to 10.0 by NH3·H2O under N2 at 80℃. The reaction was

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kept for 2 h after cooling down to 50℃. The brown product was collected by magnetic separation, washed with water and alcohol several times and then freeze-dried for 15h.

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Finally, the acquired CMGO was used in the subsequent experiments.

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2.4. Quantitative conductometric titration of -COOH The distribution of -COOH in CMGO was determined by conductometric titration at 25℃. Briefly, 1.00 g of CMGO nanoparticls was added into 100 mL

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non-CO2 ultrapure water, and the mixed solution was adjusted to the 8.0 using 0.0960 mol/L NaOH, which was ultrasonically agitation under N2 for 1 h. Then, the mixed

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solution was reversely titrated at 0.5 mL/min using 0.0209 mol/L HCl under ultrasonically agitation until the pH value was about 3.0. The conductances were monitored continuously by a DDSJ-308A conductometer (Leici, Shanghai, China).

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The same procedure was in triplicates. The total amount of -COOH on the surface of the particles and those free in aqueous phase can be calculated based on the following equations:

cs 

vs cHCl m

cf 

v f cHCl m

where vs and v f are volume of the HCl required for titration of the surface bound

acid and free acid respectively, cHCl is concentration of the standard HCl, m is the mass of the CMGO on mixed solution sample.

2.5 MSPE procedures The schematic MSPE procedures based on CMGO (MSPE-CMGO) are shown in Fig. 1. The pH value of 200.0 mL water sample was adjust to 4.0 by acetic acid. Then,

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15.0 mg of the CMGO was activated by 3.0 mL methanol and dispersed into the

aqueous solution. The mixture was shaken on a slow-moving platform shaker for 20.0

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min to capture the analytes completely. After that, the CMGO containing target

analytes was transferred by magnetic separation technology. The target analytes were desorbed in two replicates from the CMGO with 2.0 mL methanol containing 1% (v/v)

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ammonia by vortexing for 1.0 min. The collected desorption solution was evaporated

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to dryness uner a gentle N2 flow at 25℃, and then the residue was redissolved to

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100.0 μL with initial mobile phase. The resulting solution was filtered with 0.22 μm

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3. Results and discussion

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PTFE filter membrane prior to UHPLC-MS/MS analysis.

3.1. Characterization of CMGO

The morphological characteristics of GO, CGO and CMGO are shown in Fig

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2a-c by SEM. The GO composites were assembled by lots of crumpled sheet-like structure and the surface was smooth (Fig. 2a). In comparison, the CGO nanoparticles

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showed a rough surface, suggesting that the carboxylic group was well distributed and bonded to the GO surface (Fig. 2b). After combination of carboxylic functional groups with Fe3O4, it could be observed that the magnetic nanoparticles (MNPs) were

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disorderly decorated on the surface of CGO (Fig. 2c). These observations confirmed that spherical Fe3O4 nanoparticles were successfully attached on the CGO. The surface morphology and size of CMGO were characterized by TEM, BET and BJH measurements. The black spots showing Fe3O4 and transparency areas as thin films of a few layers of CGO (Fig. 2d). The TEM image shows that MNPs were aggregated because of the magnetic dipolar interaction among them. This indicates

the

successful

synthesis

of

magnetic

core/shell

particles.

The

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adsorption-desorption isotherm (Fig. 3a) was demonstrated to characterize the mesoporous property of the CMGO. It shows a type-IV curve with a small hysteresis, indicating typical mesoporous distribution features. The narrow pore size distribution derived from adsorption branch (inner of Fig. 3a) exhibited a mean pore size of 3.735 nm for the composites while using the BJH method. The results indicated that the

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obtained CMGO was of micropore type with BET specific surface area of 171.4 m2·g-1, total pore volume of 0.186 cm3·g-1. Consequently, the a larger surface area and

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higher porosity in CMGO were observed than those of the magnetic mesoporous materials in previous report owing to the hybridization to graphene [29]

The magnetic property of the as-prepared of MGO and CMGO materials were

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investigated using a VSM at room temperature. As shown in Fig. 3b, the magnetic

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hysteresis loops of MGO and CMGO showed almost zero coercivity and remanence,

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which the maximum saturation magnetization (Ms) were 49.2 and 29.6 emu·g-1, repectively. The decrease in the magnetic stren gth results from the mass effect of

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CGO shell. The CMGO loaded with the target analytes could be separated readily

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from sample medium due to the super-magntism and large saturation magnetization. The presence of functional groups on the GO, MGO and CMGO was analyzed using FT-IR spectra shown (Fig. 4a). The strong adsorption peak in the region of

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3500-3200 cm-1 is assigned to O-H stretching vibration for hydroxyl and carboxyl. The peaks at 1676 cm-1 and 1409 cm-1 are attributed to C=O and O=C-O stretching

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vibrations from carboxylic groups. Peaks can be observed at 1095 cm-1 in pure GO, 580 cm-1 in MGO and CMGO, which correspond to C-O and Fe-O vibrations, respectively. The characteristic absorption peaks of carboxyl groups (1676 cm-1 and

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1409 cm-1) were remarkably increased from GO or MGO to CMGO. These results indicated that efficient carboxylation of GO had achieved and magnetic particles were covalently bonded to carboxylated GO successfully. The conductometric titration of -COOH showed that the amount of -COOH bounded on the CMGO surface and free in aqueous phase was 0.18 and 0.22 mmol/g, respectively (Fig. 4b). 3.2. Optimization of the MSPE conditions

The spiked samples containing eight SAs at 100.0 ng/L were prepared by fortifying the stock standard solutions into 200 mL deionized water. The experimental parameters of the MSPE extraction, involving the amount of CMGO, extraction time, pH and ionic strength of the sample solution and desorption conditions, were rigorously investigated to achieve high extraction recovery (ER). 3.2.1. Effect of the amount of magnetic adsorbents

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The amount of magnetic adsorbents could directly affect the extraction efficiency

of analytes. Different amounts of CMGO (5.0-20.0 mg) were evaluated to extract SAs

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from water sample. As shown in Fig. 5 (a), the ERs for seven SAs increased with

increase in amount of magnetic adsorbents while SQX kept a stable trend. The ERs reached the maximum value when the amount of magnetic adsorbent was 15.0 mg and

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then it keeps nearly unchanged. The results indicated that 15.0 mg adsorbent was

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sufficient to fulfill the extraction process. Thus, 15.0 mg of CMGO was selected as

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the appropriate amount of magnetic adsorbents in the following studies. 3.2.2. Effect of extraction time

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MSPE is not an exhaustive extraction but a partition equilibrium process of the

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analytes between adsorbents and sample solution, which means the maximum adsorption amount of analytes would be obtained at partition equilibrium. On the other hand, a good dispersion of adsorbent was beneficial to the improvement of

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adsorption efficiency in the least time, due to the large contact surface area between the adsorbent and analytes in water sample. In this experiment, the effect of extraction

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time on the ERs for SAs was investigated in the range of 5-30 min. Fig. 5b showed that the ERs exhibit a remarkable increase from 5.0 to 15.0 min and then the upward trend become slower gradually in the following 5.0 min. The extraction reached

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equilibrium and the peak area of analytes nearly reached a maximal value when extraction time was 20.0 min. Therefore, 20.0 min of extraction time was chosen. 3.2.3. Effect of pH and ionic strength of the sample solution The existing form and stability of target analytes is attributed to the pH value of water sample. The pKa values of eight SAs in aqueous solution ranged from 5 to 7, resulting in the SAs to be positively charged at acidic conditions and negatively

charged at alkaline conditions. Additionally, alkyl carboxylic (-COOH) functional groups on the surface of CMGO have pKa of 4.5. At pH of 2, all carboxylic groups are protonated with natural charge; while pH increases to 5, about 80% of the carboxylic groups are deprotonated (-COO-) and become negatively charged and when pH reaches to 9, all the carboxylic groups are negative charged after deprotonation. To evaluate the effect of sample pH on the ERs for SAs, it was

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examined in a range of 2.0-11.0. As shown in Fig. 6, the ERs gradually rised with increasing pH from 2.0 to 4.0 and then decreased considerably with the further

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increase of pH from 5.0 to 11.0. The SAs were positively charged and part of the alkyl

carboxylic groups was deprotonated and negative charged at pH between 4.0 and 5.0. As a result, except for the hydrophobic and π-π interactions of GO, the positively

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charged SAs could electrostatically interact with the negative charged carboxylic

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groups (-COO-) linked to CMGO, leading to high extraction efficiency at a sample pH

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4.0-5.0. Consequently, the pH of the samples was adjusted to 4.0 for further studies. To investigate the effect of ionic strength on the ERs for SAs, the different

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concentrations of NaCl (0-20%, w/v) were added into the sample solution. The results

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showed that no obvious improvement was observed for the ERs for SAs. Hence, the ionic strength of water sample was not adjusted in all the subsequent experiments. 3.2.4. Effect of desorption conditions

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The solubility of SAs was excellent in water with relatively low LogKow in the range of 0.19-0.89. The stability and desorption efficiency of SAs on the sorbent is

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related to the polarity and pH value of desorption solution. Based on the above considerations, methanol, acetonitrile, acetone and ethyl acetate (all of the four solvents contained 1% ammonia) were chosen as the desorption solvents to elute eight

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SAs. It can be seen from Fig. 7a that methanol gave the stronger eluting efficiencies in comparison with other solvents under the same extraction and desorption conditions. The effect of ammonia percentage in methanol was also studied in the range of 0-5.0 % (v/v). The result indicated that the desorption efficiency of methanol containing 1% ammonia was superior to pure methanol. When the percentage of ammonia was higher than 1.0 %, the ERs of SAs decreased slightly. This is probably

because SAs will be less positive charged in an alkaline medium, resulting in weakening the affinity with sorbent. Both ammonia cations and SAs can react with carboxyic groups linked to CMGO, and the former reaction is much easier than the latter, facilitating elution of the SAs [30]. Thus, methanol containing 1.0 % ammonia was selected as the optimum desorption solvent. The effects of desorption solution volume and desorption time on the desorption

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efficiency of the analytes were also investigated in detail (Fig. 7b). The desorption

efficiency of SAs increased with the increase of the desorption solvent volume in

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range of 1.0-4.0 mL, and no obvious changes were observed when the volume was

further increased from 4.0 mL. It was found that all the analytes could be nearly completely desorbed from the sorbent by vortexing for 1 min with 2.0 mL desorption

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solvent for two times. The desorption time had no obvious influence on the desorption

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efficiency. Therefore, 4.0 mL methanol containing 1% ammonia (2.0 mL×2) with

3.2.5. Maximal extraction volume

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vortexing for 1 min was used for desorption of the SAs from the sorbent.

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In order to obtain the maximal extraction efficiency and lower LODs, the

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maximum applicable sample volume was explored for the enrichment of trace analytes. The different sample volumes (20.0-200.0 mL) containing 100.0 ng/L of SAs were investigated in the optimal enrichment conditions. The ERs of SAs increase

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from 20.0 to 150.0 mL and then remains essentially constant thereafter. So, the satisfactory concentration factor of 1000 was achieved, which demonstrates the

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feasibility of sample determination with different analyte concentration levels. 3.3. Reusability of CMGO As for the reusability of magnetic adsorbent, CMGO was used in MSPE

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procedure repeatedly and continuously. The adsorbent was washed for three times with methanol and ultrapure water, respectively, before applied in the next extraction and desorption. As can be seen from Fig. S1, the ERs for eight SAs decreased within 20% in ten recycles and approximately 10% in six recycles. The results suggested that the adsorption efficiency of CMGO for the concentration of SAs remained nearly

constant at least six times. As a result, CMGO could be considered as an ideal adsorbent because of the excellent stability and reusability. 3.4. Comparison with MGO and a traditional packed SPE cartridge A series of experiments were carried out under the optimized extraction conditions to compare the ERs of CMGO with those of MGO for the SAs. The extraction efficiencies for SAs were prominently improved by CMGO, which were

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increased by 22.3, 30.4, 38.6, 25.0, 31, 12.7, 22.0 and 0.9% for SPD, SDZ, SMZ, STZ, SMR, SMT, SCP and SQX, respectively (Fig. S2). As compared to MGO (57.1%),

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the average recoveries of eight SAs were increased by 22.8%. This might be on

account of the more carboxylic functional groups on the CMGO, which form electrostatic interaction or hydrogen bonding with analytes, resulting in satisfactory

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ERs for eight SAs. In addition, the optimal amount of CMGO was less than that of

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MGO.

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The ERs of the CMGO was compared to a traditional packed SPE cartridge with HLB sorbent. The recoveries for CMGO sorbent of SPD, SDZ, SMZ, STZ, SMR,

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SMT, SCP and SQX were 74.3 ± 1.9, 78.8 ± 3.2, 75.7 ± 4.5, 73.2 ± 4.3, 77.6 ± 3.5,

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84.1 ± 3.7, 89.9 ± 3.4 and 85.7 ± 2.9 %, respectively. For the traditionally packed SPE cartridge, the recoveries were 74.5 ± 3.9, 68.0 ± 2.3, 71.7 ± 4.1, 76.0 ± 3.8, 78.6 ± 5.2, 83.1 ± 3.0, 81.3 ± 3.7 and 77.2 ± 2.6 %, respectively. The average ERs for eight SAs

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by HLB sorbent were comparable with those by CMGO (Fig. S2). 3.5. Validation of method performance

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The applicability of this proposed method for the determination of eight SAs in

water samples was evaluated by investigating several analytical indexes under the optimal experimental conditions. The calibration curves of the SAs were established

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by plotting the peak area versus the concentration of spiked samples (n=5). Table 1 summarizes the analytical performance of this MSPE-CMGO method such as linear range, calibration equation, correlation coefficients of determination (R2), limits of detection (LODs), limits of quantification (LOQs), enrichment factor and relative standard deviations (RSDs). Good linear relationships were obtained for the STZ and SMT in the concentration range of 5.0-1000.0 ng/L, meanwhile, the other six

chemicals were in the range of 10.0-1000.0 ng/L. The R2 values ranged from 0.9983 to 0.9998, suggesting that the linearity is satisfactory in the linear range of the analytes. The LODs, calculated as a concentration at signal-to-noise ratio (S/N) of 3, were 0.49-1.59 ng/L, and the LOQs, based on signal-to-noise ratio (S/N) of 10, were 1.64-5.29 ng/L. The enrichment factors (EFs) were determined by calculating the ratio of the

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concentration of each sulfonamide after MSPE-CMOG procedure to initial concentration (100.0 ng/L) of sample solution, ranged from 1320 to 1702. The

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repeatability was assessed by means of the intra-day and inter-day RSDs at the concentration of 100.0 ng/L. The intra-day precisions were measured for five replicate

procedures in a single day and the RSDs of the peak areas ranged from 2.0 to 6.8%.

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The inter-day precisions were calculated on five consecutive days and the RSDs of the

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peak areas ranged from 3.7 to 8.6%. These results demonstrated a high sensitivity and

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excellent repeatability of this proposed method.

The interference of determination was significant for target analytes due to the

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many interfering substances present in the real environmental water samples.

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Furthermore, the accuracy and precision of the proposed method was influenced by affecting the chromatographic signal of the target analytes. Therefore, the matrix effect (ME) was evaluated by the determination of unspiked and spiked (10.0 ng/L)

ME (%) 

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real water sample. The formula for calculation was as follows: Ae 100% As

where Ae and As were the chromatographic peaks of the spiked water and standard solution. The result indicates that the water matrix had significant effect and the

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quantitative determinations should be carried out by the working curve procedure, especially standard addition procedure. 3.6. Analysis of environmental water samples To further confirm the practical reliability of this developed method for the analysis of SAs in real samples, it was applied to the determination of analytes in waterwork outlet, aquaculture water 1# and 2#. The recoveries of SAs were assessed

by spiking the analytes into water samples with three known concentrations of 10.0 and 100 ng/L. Five parallel tests were performed for each concentration level. As summarized in Table 2, below detectable levels of SAs were observed in either river water or tap water samples. However, SDZ, SPD and SMZ were detected to be 28.0, 6.38 and 60.5 ng/L, respectively, in the aquaculture water 1# water samples. The ERs of spiked water samples are in the range of 82.0-106.2% with RSDs of 1.3-7.2%. As a

IP T

result, the recovery and precision of this method were satisfactory, which could meet

the requirements for the determination of SAs in real-world waters. The

SC R

UHPLC-MS/MS chromatograms of SAs in spiked and unspiked aqiiuaculture 1# water are shown in Fig. 8. 3.7. Comparison with other methods

U

As summarized in Table 3, the analytical performance of this proposed method

N

was compared with some previously reported methods in terms of sorbent amount,

A

LOD, enrichment factor and recovery. The extraction of trace organic pollutants by SPE and MSPE involves three consecutive procedures: adsorption, elution and

M

concentration. The total time of this presented method is about 30 min, which is

ED

comparable with other methods due to the same procedures. However, the newly developed method exhibits a series of advantages such as lower LOD, maximal extraction volume, higher enrichment factor and satisfactory recovery compared with

PT

most other methods. As a result, CMGO can be used in MSPE, which is feasible for rapid and effective analysis of SAs from water samples.

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4. Conclusions

In this work, a magnetic material of CMGO was fabricated by the nucleophilic

substitution in-situ co-precipitating method, and successfully applied in MSPE for the

A

enrichment of the eight SAs coupled with UHPLC-MS detection in water samples. The developed method has the advantages of simplicity and rapidity as well as high enrichment factor resulting from its convenient magnetic separation and strong adsorption capacity of the CGO. With the aid of an external magnetic field, the sorbent is not required to be packed into the cartridge, and thus the prominent drawbacks in traditional SPE can be avoided such as column-blocking and

requirement of high pressure. Meanwhile, the phase separation can be realized easily by means of an external magnetic field without the need of additional centrifugation or filtration. Furthermore, the satisfactory LOD and recoveries can be achieved using a less amount of nanoparticle adsorbents for the concentration of trace SAs in large-volume environmental water. The matrix interferences were eliminated and the detection sensitivity was enhanced. The results demonstrated the analytical procedure

IP T

can eliminate matrix interferences and enhance the detection sensitivity. The

feasibility of the proposed method may be a useful guidance for preconcentration and

SC R

extraction of other ammonium-based organic pollutants in complex matrices.

U

Acknowledgements

N

This work was jointly supported by the National Natural Science Foundation of

A

China (51778390, 21876125), the Major Project of Natural Science Foundation of the Higher Education Institutions of Jiangsu Province (No: 15KJA610003) and Natural

M

Science Foundation of Jiangsu Province, China (No: BK 20150284). Authors also

ED

acknowledge support from the Preponderant Discipline Construction Project in higher education of Jiangsu Province, China and Jiangsu High Education Collaborative

CC E

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PT

Innovation Center of Water Treatment Technology and Material.

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sorbent for fully automated online solid-phase extraction with LC–MS determination of sulfonamides in bovine milk samples, J. Sep. Sci. 41(2018) 2237-2244 [33] P Tomai, A Martinelli, S Morosetti, R Curini, S Fanali, A Gentili, Oxidized

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drugs in river water, Anal. Methods 9 (2017) 4228-4233. [35] X Jia, P Zhao, X Ye, L Zhang, T Wang, Q Chen, X Hou, A novel metal-organic framework composite MIL-101(Cr)@GO as an efficient sorbent in dispersive micro-solid phase extraction coupling with UHPLC-MS/MS for the determination of sulfonamides in milk samples, Talanta 169 (2017) 227-238.

IP T SC R U N

A

CC E

PT

ED

M

A

Fig.1. Schematic illustration of the synthesis for CMGO and the MSPE procedure for the determination of SAs in water

Fig.2. SEM images of (a) GO, (b) CGO, (c) CMGO, and (d) TEM image of CMGO

(b) 60

100

0.2 0.1 0.0 1

10

100

Pore diameter / nm

80 Absortion

60

Desorption

40 20 0.0

0.2

0.4

0.6

0.8

40

MGO

20

CMGO

0 -20 -40 -60

1.0

-30000 -20000 -10000

Relative pressure / P/P0

IP T

120

0.3

-1

140

Magnetization (emu g )

0.4

Pore volume / cm3 g-1)

Volume adsorbed / cm3 g-1 STP

(a) 160

0

10000 20000 30000

Magnetic Field (Oe)

(b) 1200 1100

3417

3412

580

1632

3241

MCGO

M

1409

900 800

A

MGO

1409 1665

1000

N

1394 1095 1676

Conductance(S/cm-1)

GO

U

(a)

Transmittance

SC R

Fig.3. (a) N2 sorption-desorption isotherms of the as-prepared CMGO coreshell microspheres measured at 77K, (b) The magnetic hysteresis loop of the MGO and CMGO nanocomposites

700 600 500

577

4000

3600

3200

2800

2400

2000

1600

1200

800

400

400

0

10

-1

20

30

40

50

60

Volume of HCl solution (mL)

ED

Wavenumber (cm )

4500

3500

A

4

Peak area (10 )

4000

3000 2500 2000 1500 1000

(b) 5000

SPD SDZ SMZ STZ SMR SMT SCP SQX

4500 4000

Peak area (10 )

SPD SDZ SMZ STZ SMR SMT SCP SQX

CC E

(a) 5000

3500

4

PT

Fig.4. (a) FTIR spectra of GO, MGO and CMGO and (b) condutometric titration curves of CMGO

3000 2500 2000 1500 1000 500

500

0

0 5

10

15

Amount of CMGO (mg)

20

0

5

10

15

20

25

30

Extraction time (min)

Fig.5. Effect of CMGO amount (a) and extraction time (b) on extraction efficiency

35

Water sample , 200.0 mL; pH, 4.0; elution solvent, methanol (2.0×2mL). The concentration of the SAs, 100 ng·L-1 (a) extraction time, 10.0 min; (b) magnetic adsorbent, 15.0mg.

5000

3500

4

Peak area (10 )

4000

3000 2500

IP T

SPD SDZ SMZ STZ SMR SMT SCP SQX

4500

2000

1000 500 0 2

4

6

8

10

pH

SC R

1500

12

A

N

U

Fig.6. Effect of pH value on extraction efficiency Water sample , 200.0 mL; magnetic adsorbent, 15.0mg; extraction time, 20.0 min; elution solvent, methanol (2.0×2mL). The concentration of the SAs, 100 ng·L-1.

3500

4

Peak area (10 )

4000

ED

3000 2500 2000

1000 500 0 Ethyl acetate

PT

1500

Acetone

Acetonitrile

SPD SDZ SMZ STZ SMR SMT SCP SQX

4500 4000 3500 3000 2500 2000 1500 1000 500 0

Methanol

Type of desorption solution

CC E

(b) 5000

4

M

4500

SPD SDZ SMZ STZ SMR SMT SCP SQX

Peak area (10 )

(a) 5000

0

1

2

3

4

5

6

Volume of methanol (1.0% ammonia) (mL)

Fig.7. Effect of desorption solvent type (a) and volume (b) on extraction efficiency Water sample , 200.0 mL; magnetic adsorbent, 15.0mg; pH, 4.0; extraction time, 20.0 min; The concentration of the SAs, 100 ng·L-1 (a) elution solvent (2.0×2mL). (b) elution solvent, methanol (1.0% ammonia).

A

7

IP T

A

CC E

PT

ED

M

A

N

U

SC R

Fig. 8. UHPLC-MS/MS chromatograms of (a) spiked (10.0 ng·L-1) and (b) unspiked aquaculture water 1# samples Water sample , 200.0 mL; magnetic adsorbent, 15.0mg; pH, 4.0; extraction time, 20.0 min; elution solvent, methanol (1.0% ammonia, 2.0×2mL).

Table 1 Linear range, calibration equation, coefficients of determination, limit of detection, limit of quantification, enrichment factor and RSDs of eight SAs

SMZ

5.0-1000.0

STZ

10.0-1000.0

SMR

5.0-1000.0

SMT

10.0-1000.0

SCP

5.0-1000.0

SQX

5.0-1000.0

0.49

1.64

0.58

ED PT CC E A

RSD (n=5) Intra-day (%)

Inter-day (%)

1490

4.4

3.7

1.93

1400

2.0

4.8

1.21

4.05

1436

2.7

6.8

1.59

5.29

0.76

2.54

0.76

2.53

0.96 0.79

IP T

5.0-1000.0

0.99 83 0.99 98 0.99 91 0.99 89 0.99 83 0.99 94 0.99 97 0.99 96

Enrichment factor

SC R

SDZ

y=32417x+1.2× 105 y=29912x+3.2× 104 y=24828x-9.6× 104 y=15304x-1.4× 105 y=26958x+1.0× 105 y=29739x-1.7× 105 y=24462x-7.1× 104 y=42704x-1.0× 105

LOQ (ng/L)

1320

5.1

6.4

1372

5.3

6.1

1702

5.7

7.7

3.21

1686

6.8

8.6

2.62

1664

5.5

7.8

U

5.0-1000.0

R2

LOD (ng/L)

N

SPD

Calibration equations

A

Linear range (ng/L)

M

Analy tes

Found, spiked recoveries and RSDs of the sulfonamide in waterwork outlet, aquaculture water 1 # and aquaculture water 2 # samples (n=5) Aquaculture water 1#

Waterwork outlet

SMR

SMT

SCP

Found

Recovery

RSD

(ng/L)

(%)

(%)

(ng/L)

(%)

(%)

(ng/L)

(%)

(%)

0

ND

-

-

6.38

-

6.8

ND

-

-

10

9.33

93.3

3.4

10.14

101.4

2.7

9.33

93.3

3.4

100

98.3

98.3

4.1

87.5

87.5

2.7

91.5

91.5

3.6

0

ND

-

-

28.0

-

5.3

ND

-

-

10

9.22

92.2

5.5

9.47

94.7

3.5

10.14

101.4

2.7

100

89.7

89.7

2.4

81.4

81.4

12.5

92.5

92.5

5.1

0

ND

-

-

-

3.1

ND

-

-

10

9.1

91.0

3.9

8.72

87.2

1.4

10.22

102.2

5.5

100

90.3

90.3

2.7

93.5

93.5

0

ND

-

-

ND

-

10

8.5

85.0

1.3

9.6

96.0

100

94.6

94.6

2.6

89.1

89.1

0

ND

-

-

ND

-

10

9.1

91.0

3.9

8.72

100

95.2

95.2

3.5

98.7

0

ND

-

-

ND

10

8.2

82.0

5.1

100

97.2

97.2

6.1

0

ND

-

10

10.43

104.3

100

103.5

0

ND

10

8.4

100

89.4

CC E A

60.5

IP T

RSD

4.1

93.6

93.6

5.3

-

ND

-

-

2.7

9.47

94.7

3.5

5.0

101.3

101.3

7.2

-

ND

-

-

87.2

1.4

8.5

85.0

1.3

98.7

1.4

94.3

94.3

1.5

-

-

ND

-

-

9.41

94.1

4.9

10.62

106.2

2.8

103.2

103.2

1.9

93.4

93.4

7.2

-

ND

-

-

ND

-

-

5.4

9.27

92.7

1.7

8.72

87.2

5.1

103.5

2.7

101.4

101.4

5.9

99.47

99.5

5.6

-

-

ND

-

-

ND

-

-

84.0

2.5

10.4

104.0

3.6

9.41

94.1

4.9

89.4

4.4

97.9

97.9

3.3

99.1

99.1

2.0

PT

SQX

Recovery

SC R

STZ

Found

U

SMZ

RSD

N

SDZ

Recovery

M

SPD

Aquaculture water 2#

Found

(ng/L)

ED

Analytes

Spiked

A

Table 2

Comparison of proposed method with other methods applied for SAs Amount of Sample (mL)

LOD (ng/L)

Recov ery (%)

Enric hment factor

Ref.

Environ mental water

120.0

500

3.0-4. 7

62.2-9 1.1

500

[31]

-

1

1.50-2 .25 (μg/m L)

74-93

-

[32]

Surface Water

908 mm2 per side

500

3.0-28 6

HPLC-MS /MS

River water

100

100

0.0340.24

UHPLCMS/MS

Milk

5

5

UHPLCMS/MS

Environ mental water

200

HPLC-MS

SDM, SMR, SMT, SMX SQX

On-line ILSPEb

HPLC-MS /MS

Milk

SA, SMZ, SMR, SDZ, SMT, SCP, SDX, SQX, SG

BPc@SD-S PE

HPLC-MS /MS

22 SAs

3D-Mag-C MGOd SPE

SPD, SMR, SMZ, SMT, SMP, SMM, SCP, SDX, SQX, SDMX

MIL-101(C r)@GO DMSPE

a b

MSPE-CM GO

15.0

1000

[33]

84.0-9 2.0

100

[34]

12.0-1 45

79.8-1 03.8

10

[35]

0.49-1 .59

83.2-1 09.2

13201702

Pres ent wor k

M

SPD, SDZ, SMZ, STZ, SMR, SMT, SCP, SQX

Magnetic surface double-template molecularly imprinted polymers A silica-based 1-butyl-3-methylimidazolium hexafluorophosphate Oxidized buckypaper

d

Three-dimensional interconnected magnetic chemically modified graphene oxide

A

CC E

PT

ED

c

28

3.0-49

SC R

MSdt-MIPs a SPE

U

SMX, SMM, SMD, SDM, SQX

A

Compound

Measurem ent Method

IP T

Sample

Amount of sorbent (mg)

Sample preparation

N

Table 3