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ARTICLE IN PRESSG ModelHROMA-356954; No. of Pages 6

Journal of Chromatography A, xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

Journal of Chromatography A

j o ur na l ho me page: www.elsev ier .com/ locate /chroma

hort communication

cadmium(II)-based metal-organic framework material for theispersive solid-phase extraction of polybrominated diphenyl ethers

n environmental water samples

ao Sua, Ze Wangb, Yuqian Jiaa, Liulin Dengb,c, Xiangfeng Chena,b,∗, Rusong Zhaoa,.-W. Dominic Chanb,∗∗

Analysis and Test Center, Shandong Academy of Sciences, Jinan, Shandong, ChinaDepartment of Chemistry, The Chinese University of Hong Kong, Hong Kong Special Administrative RegionBiological Sciences Division and Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Washington, USA

r t i c l e i n f o

rticle history:eceived 13 July 2015eceived in revised form 11 October 2015ccepted 12 October 2015vailable online xxx

eywords:ispersive solid-phase extractionetal-organic framework

olybrominated diphenyl ethers

a b s t r a c t

In this study, a stable cadmium(II)-based metal-organic framework (MOF) material was designed andused as a sorbent for the dispersive solid-phase extraction (dSPE) of polybrominated diphenyl ethers(PBDEs) in environmental water samples. Gas chromatography coupled with triple quadrupole massspectrometer (GC–MS/MS), working in the negative chemical ionization mode, was used to quantifythe target analytes. Characterization of the material was performed by Fourier transform infrared spec-troscopy (FT-IR), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), elementaryanalyses (EA) and thermogravimetric analyses (TGA). The synthesized rod shape MOF is on the microlevel in size and has excellent chemical and solvent stability. The extraction conditions, including theextraction time, temperature and ionic strength, were examined systematically using response surface

nvironmental water samples methodology (RSM). Under optimized conditions, the method that was developed showed an excellentextraction performance. Good linearity (R2 > 0.99) within the concentration range of 0.25–250 ng L−1 wasobtained. Low limits of detection (0.08–0.15 ng L−1, signal-to-noise ratio = 3:1) and good precision (rela-tive standard deviation <12%, n = 6) were achieved. The developed method was applied to analyze naturaland spiked environmental water samples.

© 2015 Elsevier B.V. All rights reserved.

. Introduction

To effectively monitor the contamination levels of persistentrganic pollutants (POPs), the sample pretreatment techniques arearticularly important. The performance of solid-phase sorption-ased extraction methods is largely determined by the naturef the sorbent and the interaction between the analytes andhe sorbent [1]. Over the past few decades, various types ofanomaterials [2–4], such as carbon nanotubes [5,6], graphene

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7,8], metal-organic framework materials (MOFs) [9–12] and metalanoparticles [13,14], were developed and explored as sorbents forhe extraction of pollutants. Among the various new sorbents, MOFs

∗ Corresponding author at: Shandong Academy of Sciences, Jinan, PR China.∗∗ Corresponding author at: Department of Chemistry, The Chinese University ofong Kong, Shatin, N.T., Hong Kong Special Administrative Region.

E-mail addresses: xiangfchensdas@163.com (X. Chen), twdchan@cuhk.edu.hkT.-W.D. Chan).

ttp://dx.doi.org/10.1016/j.chroma.2015.10.039021-9673/© 2015 Elsevier B.V. All rights reserved.

gained special attention due to their unique properties, includingpermanent porosity, tunable pore size, and high surface areas [15].

Currently, many MOFs have been used as sorbents for var-ious solid-phase sorption-based extraction techniques, such assolid-phase microextraction (SPME) [16,17], magnetic solid-phaseextraction (MSPE) [18,19], and micro-solid-phase extraction (u-SPE) [20]. For example, Lee and coworkers used zeolite imidazolateframeworks (ZIF-8) as sorbents for the u-SPE of acidic drugs fromenvironmental water samples [20]. Yan’s group has systematicallyexplored the utility of MOFs as sorbents in sample pretreatmenttechniques [9]. Recently, Ouyang’s group used MIL-101 (Cr) as acoating material for the SPME of volatile and semi-volatile com-pounds [21]. Our group has synthesized Fe3O4@MOF core-shellmagnetic microspheres for the MSPE of polychlorinated biphenyls(PCBs) in environmental water samples [19]. The stability of the

II)-based metal-organic framework material for the disper-in environmental water samples, J. Chromatogr. A (2015),

MOFs in water and organic solvents is important for their appli-cation in sample pretreatment process. For example, MOF-5 isunstable in water, which limited its use in the extraction of targetanalytes in water samples [16].

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For aromatic persistent organic pollutants (POPs), mainlyydrophobic and �–� stacking interactions exist between MOFsnd target analytes in the extraction process. Besides the generaltructural features of MOFs, the adsorption and desorption pro-ess of analytes on MOF would be more feasible as compared withther sorbents. Taking metal oxide as an example, the high aromaticollutant affinity of metal oxide surface is due most probably tohe donor–acceptor electron transfer between the metal oxide andromatic ring (or oxygen) of PBDEs. However, this behavior wouldake the desorption process unfavorable under room temperature.nother major difference between MOF and other sorbent is thexistence of pore structure with variable size, which may be tunedor specific target molecule. In the dispersive solid-phase extrac-ion (dSPE) and MSPE processes, the sorbents are dispersed into theample. Small sized sorbentsare usually difficult to fully retrieve,ven with the aid of magnetic force or centrifugation [19], whichay limit the application of MOFs as sorbents, decrease the life

ycle of the sorbents, and thus affect the extraction performance.herefore, it is necessary to develop high stable and easy-retrievedOFs with good extraction performance.Polybrominated diphenyl ethers (PBDEs) are one type of widely

sed flame retardant and are added to various materials, such asuilding materials, electronics, furnishings and textiles [22]. SomeBDEs have been detected in humans, animals, and environmentaloil and water samples [23]. Although the acute toxicity remainsontroversial, the long-term effects of PBDEs on the nervous andeproductive system are a concern.

In this work, a cadmium(Cd)(II)-based stable MOF,Cd3(L)2(bpy)2.5(H2O)2]n (L = 5-(1-carboxyethoxy)isophthaliccid], was designed and used as a sorbent for the dSPE of PBDEs innvironmental water samples to promote the wider utility of MOFsn the sample pretreatment process. The synthesized MOF crystals stable in water and is at the micron level in size. The extractiononditions, including the extraction time, temperature and ionictrength, were examined systematically by using response surfaceethodology (RSM). The method that was developed was applied

o determine the concentration of PBDEs in natural and spikednvironmental water samples.

. Experimental

.1. Reagents and materials

All of the reagents were of analytical grade. Dimethyl-hydroxyisophthalate, methyl l-lactate, diisopropyl azodicar-oxylate, triphenyl phosphine and 4,4′-bipyridine were purchasedrom Shanghai Chemical Technology Co., Ltd. (Shanghai, China).etrahydrofuran (THF) and hydrochloric acid (HCl) were obtainedrom Sinopharm Chemical Reagent Co., Ltd. Methyl alcohol,thyl acetate, petroleum ether, anhydrous magnesium sulfateMgSO4) and sodium hydroxide (NaOH) were obtained from Tian-in Kermel Chemical Reagent Company, China. De-ionized water18.2 M� cm−1) obtained from a Millipore Milli-Q system (Milli-ore, Bedford, MA, USA) was used to prepare aqueous solutions forurther experiments. Standard mixtures of 7 PBDEs at a concentra-ion of 2 �g mL−1 in isooctane were purchased from AccuStandardNew Haven, CT, USA). These standards were stored in the darkt 4 ◦C and were used for the preparation of working standardolutions. A working standard (200 ng mL−1 in methanol) was pre-ared every week. Dichloromethane, acetone, and n-hexane werebtained from Tedia Company Inc., USA. Natural water samples

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ere collected from Daming Lake (Jinan, China), along with groundater (Dongying, China) and water from the Xiaoqing River (Jinan,hina). Before use, the natural water samples were filtered through

0.45-�m membrane (Tianjin Jinteng Experiment Equipment Ltd.,

PRESSA xxx (2015) xxx–xxx

Co., Tianjin, China) and stored in brown glass bottles at 4 ◦C priorto analysis.

2.2. Instrumentation

The morphology of the as-synthesized crystals was observedwith scanning electron microscopy (SEM) (SWPRATM55, Carl ZeissMicro Imaging Co., Ltd., Germany). Fourier transform infraredspectra (FT-IR) were recorded on a Nicolet Magna 750 FTIR spec-trometer. Powder X-ray diffraction (PXRD) patterns were acquiredat room temperature (298 K) on a Bruker SMART APEX CCD-baseddiffractometer. The data obtained by XRD was then treated byShelxtl, and the local coordination of metal was drawn by Dia-mond. Elemental analyses were performed on a Perkin-ElmerModel 2400 analyzer. Thermogravimetric analyses (TGA) were con-ducted under flowing nitrogen at a heating rate of 10 ◦C min−1 ona STA449C integration thermal analyzer (NETZSCH, German). 1Hnuclear magnetic resonance (NMR) was performed on a BrukerDRX-600 spectrometer. An Agilent GC system (7890A, Palo Alto,USA), coupled with a triple quadrupole (QqQ) mass spectrometer(7001B, Boston, USA), was used for all of the analytical experiments.The separation of the sorbent from the sorbent was conducted bycentrifugation (Thermo Multifuge X1R, USA). Ultrasonication wasconducted using the KQ2200 DB ultrasonic machine (Zhengzhou,China). The evaporation of solvent was performed using SY-2000rotary evaporator (Yarong, Shanghai, China).

2.3. Synthesis procedure

The ligand [5-(1-carboxyethoxy) isophthalic acid, H3L)] wassynthesized according to methods found in the literature [24].Briefly, dimethyl 5-hydroxyisophthalate (3.0 g, 14.3 mmol) wasadded in 100 mL of anhydrous THF at room temperature. Then,methyl l-(−)-lactate (1.78 g, 17.1 mmol) and triphenyl phosphate(7.48 g, 28.5 mmol) was added dropwise to a solution of diiso-propyl azodicarboxylate (DIAD, 5.77 g, 28.5 mmol) in an ice bath.The mixture was stirred at room temperature for 3 h. De-ionizedwater (70 mL) was added to the produced oil to quench the reac-tion, and the mixture was further extracted with ethyl acetate(30 mL × 2). The organic extracts were dried with anhydrousMg2SO4 and purified with petroleum ether–ethyl acetate (5:1, v/v).5-(1-carboxyethoxy)isophthalic ether (2.5 g (60%)) was obtainedas a colorless solid. The synthesis route of the ligand is shown inScheme S1. The ligand structure was further confirmed by NMR(ESI-3 and 4 in the Supporting information). The chemical shifts ofhydrogen are labeled in the figures. To synthesize the MOF, a NaOHaqueous solution was added to a solution of H3L (0.1 mmol, 0.025 g)in water (3 mL) (pH = 4). Subsequently, 4,4′-bipyridine (0.1 mmol,0.0156 g) and Cd(NO3)2·6H2O (0.25 mmol, 0.0771 g) were added.The mixture was stirred for 10 min at room temperature and thenheated in a 20-mL Teflon-lined autoclave at 100 ◦C for 72 h. Afterbeing cooled to room temperature, colorless rod-shaped crystalswere collected by filtration and washed several times with H2Oand methanol.

2.4. Extraction procedure

The extraction experiments were conducted in a 50-mL cen-trifugal tube. To perform the extraction, 25 mL of water sampleswere added to the tube, and then, 0.5 mg MOF was dispersed andmixed to produce a homogenous aqueous solution. The extractionwas conducted under ultrasonication for 5 min. Then, the sorbent

II)-based metal-organic framework material for the disper-in environmental water samples, J. Chromatogr. A (2015),

was collected by centrifugation (5 min, 5000 rpm). After removingthe aqueous solution, 2 mL of n-hexane was added into the tube asan eluent under ultrasonication for 5 min. After centrifugation, thecollected eluent was concentrated using a gentle stream of nitrogen

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t 30 ◦C. The obtained extract was diluted with hexane to 100 �L,rom which 1 �L was used for GC–MS analysis.

.5. GC–MS analysis

The GC separation was performed using a fused silica HP-MS capillary column with a length of 15 m × 0.25 mm and a filmhickness of 0.25 �m (Agilent Technologies. Inc., USA). The ovenemperature was held at 150 ◦C for 1.0 min and programmed toncrease at a rate of 15 ◦C min−1 until 300 ◦C, where the temperature

as held for 8 min. Helium 5.0 was used as carrier gas at a flow of.5 mL min−1. The interface temperature was set to 290 ◦C. The neg-tive chemical ionization (NCI) source temperature was selected at50 ◦C. Methane 5.5 was used as a reagent gas with an optimal flowf 40%. To enhance the sensitivity, the selected ion monitoring (SIM)ode was applied. The experiments were performed by monitor-

ng the two most intense isotope peaks from the correspondingass spectra m/z 79 and 81 ([Br]−), of which the most intense peak

rom the NCI spectra (m/z 79) was used for quantification. In NCIondition, it is also possible to analyze PBDEs in multiple reactiononitor (MRM) in MS/MS mode. However, the sensitivity should

e much lower as compared with the SIM mode for PBDEs due tohe low abundance of the precursor ions [M−xH−yBr]−. It has beeneported that the sensitivity of PBDEs analysis under EI conditions lower than that of NCI condition [25–27]. Thus, the high sensitiv-ty of GC–NCI/MS rendered it the most commonly used method fornalysis of major PBDEs. Although a triple quadruple mass spec-rometer was used, the first quadruple working in SIM mode waselected. The collision cell and the second quadruple were set asotal ion transmission mode. The retention time and monitored ionsere shown in Table S1.

. Results and discussion

.1. Material characterization

The size and shape of the as-synthesized crystal is shown inig. 1(a). The crystal has a rod shape that is approximately 20 �mn length and 5 �m in width. The PXRD spectrum of the powder

as collected from 5 to 50◦. As shown in Fig. 1(b), the characteris-ic peaks of the experimental XRD pattern matched well with theimulated result, which indicated that the crystal had been suc-essfully constructed. The chemical composition of the crystals wasurther confirmed by FT-IR analysis (Fig. 1 (c)). The peaks at 1600nd 1477 cm−1 were attributed to the C C stretching of the aro-atic ring, and the peaks at 1258 and 1043 cm−1 were attributed to

he O group connected to the aromatic ring. As shown in Table2, the result of element analysis for the as-synthesized materials in accordance with the calculated values. Fig. 1(d) shows theocal coordination environments of the Cd center and the ligandsn the compound. The metal ions exhibited pentagonal bipyramidoordination geometry. Cd1 and Cd3 were coordinated by five car-onyl oxygen atoms and two pyridine nitrogen atoms, while Cd2as coordinated by four carbonyl oxygen atoms, two water oxy-

en atoms and one pyridine nitrogen atom. There were two typesf pores with sizes of 4.2 A × 8.2 A and 4.9 A × 6.2 A, respectively.he 3D network and the crystal data in CIF format were shown inhe supporting information.

.2. Optimization of dSPE

The extraction and desorption step in the dSPE process was opti-

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ized separately. In the optimization of the extraction step, theverage mean recovery of 7 PBDEs was selected as the experimen-al response. The extraction time, temperature and ionic strengthere selected for optimization. The amount of the sorbent and

PRESS xxx (2015) xxx–xxx 3

the concentration of PBDEs remained constant. The levels of thefactors and the design matrix for the optimization are listed inTable S3. The Box–Behnken design was used to find the optimumextraction parameters through response surface methodology [22].Fig. 2(a–c) shows the response surfaces of the mean absoluterecovery of the 7 PBDEs, which were obtained by plotting theextraction time versus the temperature, the extraction time versusthe ionic strength, and the extraction temperature versus the ionicstrength, respectively. The influence of experimental conditionson the recovery of the target analytes was described using a sec-ond order model (quadratic). The extraction time and temperaturewere determined to be important parameters that strongly affectthe extraction efficiency. According to the optimization results,the extraction conditions for the dSPE of PBDEs from the watersample solutions were as follows: the extraction time = 10 min andthe extraction temperature = 32.5 ◦C. The subsequent experimentswere performed under these conditions.

The desorption solvent, the desorption time, and the volume ofthe desorption solvent were considered in the desorption step. Nocarry-over effects were observed in the two successive desorptionsteps. As shown in Fig. 2 (d), n-hexane exhibited the best des-orption performance among the solvents that were studied. ThePBDEs could be completely desorbed within 3 min of ultrasoni-cation by 2 mL of n-hexane. The optimum desorption conditionsfor the dSPE of PBDEs from the water samples were as follows:one ultrasonic desorption of 3 min using n-hexane (2 mL) as theeluent. The subsequent desorption experiments were performedunder these conditions.

3.3. Method evaluation and application

Table 1 summarizes the results of the merit analysis of theoptimized dSPE–NCI-GC–MS method using the as-synthesizedMOF. Good linearity (R2 > 0.99) within the concentration rangeof 0.25–250 ng L−1 was obtained. The limits of detection (LODs)and the limits of quantification (LOQs) were calculated usingsignal-to-noise ratios of 3 (3 × S/N) and 10 (10 × S/N), respectively.Low LODs (0.08–0.15 ng L−1) and LOQs (0.24–0.45 ng L−1) wereobtained. Repeatability (intra-day) and reproducibility (inter-day)were used to determine the precision of the method. The repeata-bility of the method was evaluated using six replicate samples(relative standard deviation, %RSD), which varied between 3.28%and 5.57%. The day-to-day reproducibility was analyzed on six con-secutive days and was found to be in the range of 2.06–4.01%.PBDE levels in local natural environmental water samples, includ-ing river water, lake water, and ground water, as well as drinkingwater, were analyzed using the dSPE method that was developed inthis study. BDE-47 and BDE-99 were detected in the river sample.For other samples, PBDEs were not detected, which was expectedby considering the absence of source for this kind of pollutantsin the local samples sites. To further test the applicability of themethod, the real water samples spiked with PBDEs in the con-centrations of 1 ng L−1, 10 ng L−1 and 100 ng L−1 were analyzed.The spiking recoveries of the target PBDEs in the natural samplesare summarized in Table 2. The recoveries for the spiked 1 ng L−1,10 ng L−1 and 100 ng L−1 samples ranged from 83.9% to 102.2%. Con-sequently, it is believed that the developed method is applicable forthe determination of PBDEs in real environmental water samples.The extracted ion chromatograms (EICs) of PBDEs obtained fromdSPE-NCI-GC–MS method in the river water sample are shown inFig. 3.

The proposed dSPE-GC–NCI-MS technique was compared with

II)-based metal-organic framework material for the disper-in environmental water samples, J. Chromatogr. A (2015),

other published methods, such as SPME-GC–MS [28], SPE-GC-ECD[29], LLME-HPLC [30] and cloud point extraction GC–MS [31]. In thedSPE process, the mass transfer and diffusion rate of target analytesbetween the sorbent and the solution phase are relative high as

Please cite this article in press as: H. Su, et al., A cadmium(II)-based metal-organic framework material for the disper-sive solid-phase extraction of polybrominated diphenyl ethers in environmental water samples, J. Chromatogr. A (2015),http://dx.doi.org/10.1016/j.chroma.2015.10.039

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Fig. 1. (a) SEM image of the as-synthesized [Cd3(L)2(bpy)2.5(H2O)2]n; (b) PXRD spectra of [Cd3(L)2(bpy)2.5(H2O)2]n; (c) FT-IR spectrum of [Cd3(L)2(bpy)2.5(H2O)2]n , and (d)local coordination environments of the Cd center and the ligands.

Fig. 2. Estimated response surface from the Box–Behnken design for the absolute mean recovery of the 7 PBDEs (a) amount of sorbent vs. extraction time; (b) extractiontime vs. ionic strength, (c) extraction temperature vs. ionic strength, and (d) the effect of type of desorption solvent on the extraction efficiency of PBDEs in water.

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Table 1Characteristic data of the developed dSPE-GC–NCI-MS method for the determination of PBDEs from drinking water samples.

Analyte Linear range (ng L−1) Correlation coefficient (r) LOD (ng L−1) LOQ (ng L−1) Repeatability (RSD, n = 6) (%) Reproducibility (RSD, n = 6) (%)

Intra-day Inter-day

BDE-28 0.25–50 0.9984 0.08 0.25 4.59 3.75BDE-47 0.25–50 0.9994 0.08 0.22 3.28 2.88BDE-99 0.35–50 0.9955 0.10 0.34 3.32 2.06BDE-100 0.25–50 0.9992 0.08 0.24 4.23 2.75BDE-153 0.35–50 0.9957 0.10 0.33 3.37 3.15BDE-154 0.25–50 0.9922 0.08 0.24 4.02 3.44BDE-183 0.50–50 0.9904 0.15 0.47 5.57 4.01

Table 2Analytical results for determination of 7 PBDEs in water samples.

Analytes BDE-28 BDE-47 BDE-99 BDE-100 BDE-153 BDE-154 BDE-183

Drinking water

Found (ng L−1) N.D.d N.D. N.D. N.D. N.D. N.D. N.D.Recoverya (%) 91.9 ± 3.7 94.3 ± 7.5 90.7 ± 2.6 91.1 ± 1.7 83.9 ± 7.8 89.6 ± 1.3 94.1 ± 1.2Recoveryb (%) 104.6 ± 5.4 99.7 ± 4.2 90.1 ± 6.3 98.8 ± 2.5 102.1 ± 9.3 96.4 ± 7.9 100.4 ± 7.3Recoveryc (%) 97.3 ± 2.9 98.4 ± 5.3 95.4 ± 8.8 95.8 ± 5.8 93.9 ± 3.4 100.7 ± 6.1 102.2 ± 3.1

River water

Found (ng L−1) N.D. N.D. N.D. N.D. N.D. N.D. N.D.Recoverya (%) 93.1 ± 2.5 94.8 ± 4.5 93.2 ± 6.1 89.3 ± 4.1 86.2 ± 1.3 86.4 ± 1.4 88.9 ± 6.6Recoveryb (%) 93.7 ± 4.4 86.7 ± 11.4 91.3 ± 7.5 90.8 ± 6.9 90.7 ± 5.8 85.7 ± 6.4 84.9 ± 3.2Recoveryc (%) 96.3 ± 2.3 92.9 ± 4.4 97.3 ± 5.5 92.4 ± 2.9 92.1 ± 4.1 97.2 ± 3.1 99.1 ± 2.7

Ground water

Found (ng L−1) N.D. 0.62 0.57 N.D. N.D. N.D. N.D.Recoverya (%) 93.1 ± 2.2 97.5 ± 1.4 94.8 ± 1.8 97.1 ± 1.4 92.1 ± 5.5 91.8 ± 4.5 94.9 ± 4.9Recoveryb (%) 93.8 ± 5.2 89.1 ± 3.7 90.9 ± 8.7 88.4 ± 3.9 91.5 ± 9.6 87.1 ± 9.2 89.6 ± 8.6Recoveryc (%) 98.1 ± 1.3 91.9 ± 2.9 94.9 ± 5.3 89.3 ± 1.3 95.6 ± 2.5 93.9 ± 1.3 92.9 ± 2.7

Lake water

Found (ng L−1) N.D. N.D. N.D. N.D. N.D. N.D. N.D.Recoverya (%) 91.1 ± 1.4 98.1 ± 3.3 98.3 ± 4.6 97.2 ± 1.1 96.2 ± 4.4 91.6 ± 3.3 97.5 ± 3.2Recoveryb (%) 86.9 ± 7.5 87.6 ± 6.8 84.7 ± 8.2 84.7 ± 8.3 84.1 ± 6.3 82.5 ± 5.1 86.5 ± 5.9Recoveryc (%) 93.9 ± 1.7 91.6 ± 3.9 98.4 ± 2.6 94.1 ± 6.2 92.6 ± 5.5 98.9 ± 6.5 94.6 ± 4.2

a Recovery of spiked 1 ng L−1.b Recovery of spiked 10 ng L−1.c Recovery of spiked 100 ng L−1.d Not detected.

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ig. 3. Typical extracted chromatogram of PBDEs of the water samples obtained byhe developed method: lake water (a), lake water spiked at 1 ng L−1 (b), 10 ng L−1 (c)nd 100 ng L−1 (d).

ompared with that SPE. Although SPME is solvent free, the extrac-ion time used in the work is usually loner than dSPE. Moreover, thePME fiber is expensive and need very careful operation. The LLME-PLC method suffers from high LODs for PBDEs analyses. Althoughaving high recovery, the cloud point extraction process is rela-ive sophisticated. As shown in Table S4, the recoveries of selectedBDEs in real water samples are higher than that of SPE, SPME andLME. In summary, the advantages of this method are primarily as

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ollows: (1) Short extraction time and high recoveries for analytes,2) simple operation and minimized consumption of solvent, and3) high sensitivity and satisfactory accuracy. Although PBDEs aren general non-polar compounds, the presence of the oxygen atom

and the resulting asymmetry about the horizontal axis makes themmore polar than other POPs, such as PAHs and PCBs. The organicligand of Cd(II)-based MOF here consisted both the non-polar andpolar functional group. Beside hydrophobic and �–� stacking inter-actions, other interaction between Cd(II)-based MOFs and PBDEsmight exist. In this study, due to the low concentration of PBDEsin the sample, it may be only adsorbed on the surface of the MOF.The effect of pore size may play a role on the extraction and needfurther investigation.

4. Conclusion

In this study, a stable Cd(II)-based MOF material was synthe-sized and used as a sorbent for the dSPE of PBDEs in water samples.Combined with GC–NCI-MS, good analytical performances withlow detection limits, short extraction times, and high extractionefficiencies were achieved. Accordingly, the proposed method wasapplied to analyze of trace PBDEs in environmental water samples.Good recoveries were obtained in analysis of the spiked real watersamples. In conclusion, the developed dSPE-GC–NCI-MS methodprocesses potential for the application in the determination ofPBDEs in real water samples.

Acknowledgements

Financial supports from the National Natural Science

II)-based metal-organic framework material for the disper-in environmental water samples, J. Chromatogr. A (2015),

Foundation of China (21205071 and 21477068), Natural Sci-ence Foundation of Shandong Province (ZR2012BQ009), KeyResearch and Development Program of Shandong Province(2015GSF117011) and Funds for Fostering Distinguished Young

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cholar and Fundamental Research Funds of Shandong Academyf Sciences are gratefully acknowledged.

ppendix A. Supplementary data

Supplementary material related to this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.chroma.2015.10.39.

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