Sensitive monitoring of benzoylurea insecticides in water and juice samples treated with multiple monolithic fiber solid-phase microextraction and liquid chromatographic analysis

Accepted Manuscript Title: Sensitive monitoring of benzoylurea insecticides in water and juice samples treated with multiple monolithic fiber solid-phase microextraction and liquid chromatographic analysis Author: Meng Mei Xiaojia Huang Keren Liao Dongxing Yuan PII: DOI: Reference:

S0003-2670(14)01485-8 http://dx.doi.org/doi:10.1016/j.aca.2014.12.047 ACA 233653

To appear in:

Analytica Chimica Acta

Received date: Revised date: Accepted date:

16-11-2014 22-12-2014 26-12-2014

Please cite this article as: Meng Mei, Xiaojia Huang, Keren Liao, Dongxing Yuan, Sensitive monitoring of benzoylurea insecticides in water and juice samples treated with multiple monolithic fiber solid-phase microextraction and liquid chromatographic analysis, Analytica Chimica Acta http://dx.doi.org/10.1016/j.aca.2014.12.047 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.

Submitted to Anal. Chim. Acta (revised)

Sensitive monitoring of benzoylurea insecticides in water and juice samples treated with multiple monolithic fiber solid-phase microextraction and liquid chromatographic analysis

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Meng Mei, Xiaojia Huang*, Keren Liao, Dongxing Yuan

State Key Laboratory of Marine Environmental Science, Key Laboratory of the

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Ministry of Education for Coastal and Wetland Ecosystem, College of the

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Environment and Ecology, Xiamen University, Xiamen 361005, China

E-mail: [email protected]

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*Corresponding author. Tel: 086-0592-2189278

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Corresponding Address: P. O. Box 1009, Xiamen University, Xiamen 361005, China

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Graphical abstract

Highlights

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A new MMF/MAED-SPME was designed and prepared.

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Preparation and extraction conditions were studied thoroughly.

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MMF/MAED-SPME can extract benzoylurea insecticides (BUs) effectively.

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Sensitive determination method for BUs in water and juice samples was developed.

Abstract

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In present study, a convenient, sensitive and environmentally friendly method for the

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determination of five benzoylurea insecticides (BUs) in water and juice samples was developed. To extract trace benzoylurea insecticides effectively, poly (methacrylic

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acid-co-ethylene dimethacrylate) monolith was prepared and used as the sorbent of

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multiple monolithic fiber solid-phase microextraction (MMF-SPME). The influences of preparation conditions of monolith and extraction parameters of MMF-SPME on

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BUs were studied thoroughly. Under the optimized conditions, the combination of

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MMF-SPME with high performance liquid chromatography-diode array detection

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(MMF-SPME-HPLC-DAD) showed expected analytical performance for target

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analytes. The limits of detection (S/N= 3) of the developed method were 0.026-0.075

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μg L-1 in water and 0.053-0.29 μg L-1 in juice samples. Good linearity was obtained for analytes with the correlation coefficients (R2) above 0.99. Satisfactory

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repeatability and reproducibility was achieved, with relative standard deviations (RSD) of both less than 10%. Finally, the established MMF-SPME-HPLC-DAD method was

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successfully applied for the determination of BUs residues in juice and environmental

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water samples. Recoveries obtained for the determination of BUs in spiking samples ranged from 65.1% to 118%, with RSD below 10% in all cases.

Keywords: Multiple monolithic fiber solid-phase microextraction (MMF-SPME) Monolith;

Sorbent;

chromatography

Benzoylurea

insecticide;

High

performance

liquid

1. Instruction Benzoylurea insecticides (BUs) have been widely used for the control of insects and act as powerful insect growth regulators because of their attractive properties, which include their insecticidal activities, tremendous selectivity and rapid degradation [1-3]. However, the presence of residues in foods and the environment due to their great consumption on agrochemical could lead to chronic exposure and

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long-term toxicity effects [4]. Therefore, developing sensitive, simple and

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environmentally friendly analytical techniques for the monitoring of BUs are necessary.

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Among the analytical methods developed for the determination of BUs, high-performance liquid chromatography (HPLC) is the most commonly used

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technique for the analysis of BUs in different samples because of its simplicity, high

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sensitivity and broad linear range [5, 6]. However, sample pretreatment steps are

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required before the analysis because of the complexity of the matrices in real samples

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and the trace level of BUs. So far, liquid-liquid extraction (LLE) [7], liquid-phase

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microextraction (LLME) [8, 9], solid-phase extraction (SPE) [6, 10] and solid-phase

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microextraction (SPME) [11] have been applied for the analysis of BUs in all kinds of samples. However, LLE and SPE are slow, labor-intensive and environmentally

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unfriendly. The extraction capacity of LLME is limited because of the low extractant is used. Compared with other extraction methods, SPME is simple, convenient, and

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flexible

environmentally

friendly.

Vázquez

et

al

used

commercial

polydimethylsiloxane/divinylbenzene (PDMS/DVB, 60 µm) coated fiber to extract six

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BUs from orange juice [11]. However, the extraction capacity was limited because the coatings were thin and low extraction media were employed. Furthermore, in their study, non-equilibrium extraction was utilized because some BUs did not reach extraction equilibrium even if the extraction time was prolonged to 60 min. There are some disadvantages of non-equilibrium extraction. For example, to obtained

satisfactory precision, the extraction time should be controlled strictly. However, it is inconvenient in experimental operation. Therefore, to utilize the SPME to extract BUs from complicated samples matrices, developing new extraction fibers with high extraction performance is highly desired. Multiple monolithic fiber SPME (MMF-SPME) with porous monolith as extractive medium is a new extraction format which developed in our group [12, 13]. Compared with coating-based SPME fiber, there are several distinct advantages of MMF-SPME. Firstly, the MMF-SPME is consisted of four independent thin monolithic fibers. The

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total amount of sorbent in MMF-SPME is larger than that of coating-based fiber. Hereby, the MMF-SPME possesses high extraction capacity. Secondly, the porous

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monolith material possesses expected mass-transfer speed. At the same time, the

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aqueous samples can form convection during extraction because there are gaps between fibers in MMF-SPME. The formation of convection accelerates the

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extraction procedure. Therefore, the extraction speed of MMF-SPME is faster than

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that of coating-based fiber. Thirdly, the MMF-SPME is very flexible. According to

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the character of target analytes, the extraction medium-monolithic fiber can be easily

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designed and prepared to realize effective extraction of analytes. At present work, five BUs were selected as target analytes. It can be seen from their molecular structure

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(Table S1), there are hydrophobic groups-phenyl groups and strongly polar amide

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groups, amino groups and halogen atoms. According to the structural characters of

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these BUs, a porous poly (methacrylic acid-co-ethylene dimethacrylate) (MAED) monolith was prepared and used as the sorbent of MMF-SPME. In the monolith, the

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alkyl groups can interact with the analytes through hydrophobic interactions. The carboxyl groups in the sorbent can produce ion-exchange interactions with amide and

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amino groups in BUs. Therefore, the MMF/MAED-SPME is expected to extract BUs effectively through multi-interactions. After the optimization of extraction conditions, a simple and sensitive methodology combining the MMF/MAED-SPME and liquid desorption (LD), followed by high performance liquid chromatography with diode array detection (MMF/MAED-SPME-LD-HPLC/DAD) for the direct analysis of trace BUs in water and juice samples was developed.

2. Experimental 2.1 Chemicals Methacrylic acid (98%) (MA) and ethylene dimethacrylate (EDMA) (97%) were purchased from Alfa Aesar (Tianjin, China). Azobisisobutyronitrile (AIBN) (97%, recrystallized before use), 1-propanol (97%), 1,4-butanediol (98%) and acetic acid (96%) were purchased from Shanghai Chemical Co. (China); HPLC-grade acetonitrile (ACN) and methanol were purchased from Tedia Company (Fairfield, USA); Water

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used throughout the study was purified using a Milli-Q water purification system

dimethacrylate)

monoliths

and

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(Millipore, USA). The MMF/VI-SPME based on poly (vinyl imidazole-co-ethylene MMF/AMIED-SPME

based

on

poly

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(1-allyl-3-methylimidazolium bis [(trifluoro methyl) sulfonyl] imide-co- ethylene dimethacrylate) monoliths were prepared according to our previous studies [12, 13].

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Hexaflumuron (HFU), teflubenzuron (TFU), lufenuron (LFU), flufenoxuron (FFU)

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and chlorfluazuron (CFU) were supplied by national institute for the control of

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pharmaceutical and biological products. The chemical properties of the above

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analytes are shown in Table S1. River water and farmland water samples were

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collected from Xiamen city and filtrated through 0.45 m membranes, and their

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resistivity were 6250 Ω·cm and 1320 Ω·cm, respectively. Juice samples with different brands were purchased from locally retail markets. All samples were stored at -4 °C

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before use. Individual stock solutions of BUs were prepared at a concentration of 10.0 mg L-1 by dissolving methanol and renewed monthly. Working solutions (containing a

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standard mixture for each benzoylurea) were prepared at a concentration of 100 μg L-1 to validate the method.

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2.2 Instruments HPLC analyses were carried out on a LC chromatographic system (Shimadzu,

Japan) equipped with a binary pump (LC-20AB) and a diode array detector (SPD-M20A). Sample injection was carried out using a RE3725i manual sample injector with a 20 μL loop (Rheodyne, Cotati, CA, USA). All experiments were

performed at room temperature. If there was no special indication, the data were repeated in triplicate. The morphologies of monolithic materials were examined by a Model XL30 scanning electron microscopy (SEM) instrument (Philips, Eindhoven, The Netherlands). The pore size distribution (PSD) of the monoliths was measured on a mercury intrusion porosimeter Model PoreMaster-60 (Quantachrome Instruments, Florida, USA). Elemental analysis (EA) was carried out on PerkinElmer (Shelton, CT, USA) Model PE 2400. Fourier transform infrared spectrum (FT-IR) was performed

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on an Avatar-360 FT-IR instrument (Thermo Nicolet, Madison, WI, USA). 2.3 Chromatographic conditions

The mobile phase was consisted with ultrapure water

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size, 250 mm×4.6 mm i.d.).

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The separation of BUs was conducted on a Kromasil C18 column (5 µm particle

and ACN (v/v=22/78). The detection wavelength was set at 260 nm and the flow rate

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was 1.0 mL/min. The injection volume was 20 μL.

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2.4. Preparation of MMF/MAED

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According to the in-situ polymerization technique of monolith, the preparation

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procedure of MMF/MAED is quite convenient. Two steps were involved in the preparation of MMF/MAED. In the first step, single thin poly (MA-co-ED)

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monolithic fiber was synthesized. In the all polymerization reaction, AIBN was used

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as polymerization initiator (1% (w/w) of the total monomer amount). The mixture of

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1-propanol, 1,4-butanediol and water (w/w/w=55/30/15) was used as porogen. Different concentrations of monomer and porogen were used for different fibers

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(Table 1). The monomer mixtures, porogen and AIBN were mixed ultrasonically into a homogenous solution, and then the reactant solution was purged with nitrogen for 5

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min. Subsequently, the reactant mixture was introduced into a glass capillary (0.5 mm in diameter and 10 cm in length) with the aid of a syringe. After that, both ends of capillary were sealed with two small pieces of rubber. The filled glass capillary was placed in an oven and heated at 70 ℃ for 24 h. After the polymerization, 2 cm length of glass capillary was removed and translucent thin fiber (2 cm in length and 0.5 mm

in diameter) (Fig.1a) was obtained. For comparison, single thick fiber (1.0 mm in diameter) was synthesized as the same procedure described as above. In the second step, four thin poly (MA-co-ED) monolithic fibers were carefully tied up with parafilm at the glass part of fiber to form fiber bunch. After that, the fiber bunch was dipped in methanol for 24 h to remove the residual monomers, porogen and uncross-linked polymers. Finally, the fiber bunch was dried in air for 1 h to obtain the final MMF/MAED. The Fig.1a and Fig.1b show the photos of single thin monolithic fiber and MMF/MAED with four thin fibers, respectively.

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2.5. MMF/MAED-SPME procedure At present study, stirring extraction and LD modes were used in this work. The

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MMF/MAED was activated with methanol and ultrapure water in sequence. A

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volume of 20 mL of sample solution was added into a 25 mL vial containing an 8 × 2 mm stirring bar. MMF/MAED-SPME was performed by direct immersion of the fiber

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bunch in the sample solution for 70 min under low stirring (a vortex just appeared)

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using a magnetic stirrer. After extraction, the fiber bunch was removed and desorbed

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with 400 L desorption solvent (methanol) in a 0.4 mL vial insert by stirring for 15

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min to release adsorptive analytes. To further increase the sensitivity, the stripping solvent was evaporated to dryness under a gentle stream of nitrogen. The dried

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residue was re-dissolved in 0.1 mL methanol for HPLC analysis. In order to avoid

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analyte carryover, before the next extraction, the used fiber bunch was reconditioned

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in two consecutive steps of 15 min by immersion in methanol and ultrapure water,

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respectively.

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2.6 The optimization of extraction factors In present study, to obtain satisfactory extraction performance, the effects of some

key factors including desorption solvent, extraction and desorption time, pH values and salt concentration on extraction efficiency were investigated by a step-by-step optimization scheme.

2.7 Preparation of real samples Water samples: Environmental water samples were collected in 2.5 L amber glass bottles and stored in the dark at 4 °C until analysis. All the samples were vacuum-filtered through a 0.45 μm nylon filter to remove suspended matter. After that, MMF/MAED-SPME procedure was used to extract BUs from the above-mentioned water samples. Juice samples: Firstly, the juice samples were filtered with a 0.45 µm membrane. After that, 2.0 mL of the filtrate was diluted with ultrapure water to 20 mL. The

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subsequent extraction and analytical procedure were the same as in the case of water

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samples.

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3. Results and discussion

3.1. Preparation of characterization MMF/ MAED

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Typically, preparation parameters including the content of monomer, cross-linker

sorbent.

Therefore,

the

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monolith-based

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and porogen can affect the extraction performance and useful life span of above-mentioned

parameters

were

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investigated in detail in order to obtain expected extraction performance and longevity

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of MMF/MAED. It can be seen from the data in Table 1 that the content of MA, ED

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and porogen in polymerization has strong effect of the extraction performance of MMF/MAED-SPME for the target BUs. Suitable content of monomer, cross-linker

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and porogen favors the increase of extraction performance. According to the results, and comprehensively considering extraction capacity, extraction speed and useful

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longevity of MMF/MAED, the optimal preparation conditions of the

monolithic

fiber were the proportion of MA kept 30% in the monomer mixture, the ratio of

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monomer mixture to porogen was 45/55 (%, w/w) (MMF/MAED-5). Under the optimal preparation conditions, the monolithic fiber is translucent, integrated and elastic (Fig. 1a). The fiber possesses satisfactory life span, it can be reused more than 150 times, including real samples, and no loss in their performance and no cracking of the monolith were observed. At the same time, excellent fiber to fiber reproducibility

was achieved, the RSD (n=4) of extraction efficiencies for HFU, TFU, LFU, FFU and CFU were 7.7%, 9.4%, 4.6%, 3.5% and 7.6%, respectively. EA, FT-IR, PSD and SEM were used to characterize the monolithic fiber prepared under the optimal conditions (MMF/MAED-5). EA results show that the carbon and hydrogen contents were 55.9% (w/w) and 5.66% (w/w), respectively. The EA results well indicate that MA and EDMA were polymerized successfully. The FT-IR spectrum of the monolithic fiber is showed in Fig.S1. The peaks at 2987.2 cm−1 and 2943.1 cm−1 belong to the vibrations of CH3 and CH2 groups, respectively. The

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absorption peak at 1732.0 cm−1 is ascribed to the vibrations of carbonyl groups, the absorption peak at 1069.4 cm-1 is the stretching of O-H of MA. The FT-IR spectrum

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further confirmed the polymerization of MA and ED. Fig. S2a and S2b show the SEM

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images of the poly (MA-co-ED) monolithic fiber at 30× and 10 000× magnification, respectively. It can be seen from the Fig. S2a that the fiber is integrated and

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homogeneous. At the same time, the even pore size and microglobules of the

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monolithic material can be observed (Fig.S2b). Furthermore, it can be found from the

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PSD plot that the pore size distribution is uniform, most of the pore sizes are around

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200 nm (Fig,1c). The existence of uniform pore size distribution ensures the monolithic fiber possess good permeability and favorable mass transfer during the

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extraction procedure. Furthermore, the total surface area was 46.6 m2/g for the

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material calculated from Brunauer-Emmett-Teller (BET) plot. The satisfactory large

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surface area indicates that there are abundant adsorptive sites for target analytes. Therefore, it is reasonable to expect that the MMF/MAED possesses high extract

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performance to BUs.

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3.2. Optimization of MMF/MAED-SPME method 3.2.1. Desorption solvent In this study, methanol/water (with 0.1% acetic acid) binary solvent was selected as desorption solvent. The content of water in desorption solvent varied from 0% to 20% (v/v). Fig. 2 shows that the extraction performance decreases with the increase of the proportion of water in desorption solvent. At the same time, the adsorbed BUs could

not be eluted from the fibers completely within 30 min when water was contained in desorption solvent. However, when using 100% methanol as desorption solvent, the adsorbed BUs were eluted from the sorbent quickly within 30 min. Therefore, methanol was used for subsequent experiments.

3.2.2 Extraction and desorption time The extraction time is an extremely important parameter that affects extraction performance. At present study, the extraction time was varied from 10 to 80 min and

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the extraction time profile was showed in Fig.3a. It can be seen from figure that the peak areas of the five BUs increase with the extension of extraction time. The

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extraction equilibrium was reached after 70 min of extraction. To further evaluate the

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extraction speed of MMF/MAED-SPME, the extraction time profile of thick fiber (1.0 mm in diameter and 20 mm in length; at the same time, the weight of the monolith

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was equal to the weight of the monoliths in MMF/MAED) was also studied for

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comparison (Fig.3b). As the extraction trend of MMF/MAED-SPME, the extraction

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performance enhanced with the increase of extraction time, but the equilibrium did

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not be reached even the extraction time was prolonged to 120 min, which indicated that part of the sorbents in the thick fiber had not contacted with analytes. It also can

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be see that the extraction performance of thick fiber was far lower than that obtained

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with MMF/MAED-SPME when the extraction time was 70 min. The above

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comparison well demonstrates that MMF/MAED-SPME possesses expected extraction speed and extraction capacity. The investigation of desorption time showed

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that the BUs could be eluted from the sorbent completely in 15 min when the extraction time was 70 min (Fig.S3). Consequently, 70 min and 15 min were adopted

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for extraction and desorption procedure, respectively, in the following research. 3.2.3 Sample pH value The molecular forms of BUs will be affected by the sample pH value because there are abundant polar groups in the molecules of BUs. At the same time, the carboxyl groups in the monolith will dissociate in suitable pH value. Therefore, the extraction performance of MMF/MAED-SPME for BUs will be affected obviously by the

sample pH value. Fig.4 shows the effect of pH value on extraction performance by varying the sample pH value from 2.0-11.0.

It clearly shows that the extraction

performance improves with the increase of pH values from 2.0 to 9.0, and the extraction performance decreases when pH values increase continuously. The variation trend may be explained as follows: the pKa values for target BUs are in the range of alkalinity (for example, the pKa values for FFU and CFU are 10.1 and 8.1, respectively) [3, 14]. At low pH values, the nitrogen atoms of BUs were protonated, however, the carboxyl groups in the monolith did not dissociate. Hereby, there was no

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ion-exchange interaction between sorbent and analytes. Only hydrophobic interaction between monolith and BUs contributed to the extraction. With the increase of pH

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values, carboxyl groups in the sorbent dissociated and produced ion-exchange

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interaction with analytes. Therefore, higher extraction performance could be obtained with the increase of pH values. However, when the pH values increased continuously,

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the favorable ion-exchange interactions were weakened because deprotonation

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procedure happened on nitrogen atoms of BUs, leading to the decrease of extraction

ion-exchange

interactions

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hydrophobic,

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performance. The results well demonstrate that multi-interactions such as co-contribute

to

the

extraction

of

MMF/MAED-SPME for BUs. According to the results, the sample pH value was set

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3.2.4 Ionic strength

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at 8.0 in the following experiments.

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Ionic strength, which is examined through the addition of salt, may increase or decrease the extraction efficiency because there are two opposite interactions-salting

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out effect and the electrostatic interaction [15]. Typically, salting out effect can increase the extraction efficiency. However, the electrostatic interaction between

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polar molecules and salt ions in sample solution will decrease the extraction performance. To investigate the effect of salt on the proposed method, various concentrations of sodium chloride from 0 to 25% were examined (Fig. 5). The results revealed that all of the extraction performance decreased with the addition of salt. Therefore, no salt was added during the use of the proposed method. Based on the above discussions, the following optimal conditions were used in this

new MMF/MAED-SPME method: methanol was selected as desorption solvent; extraction and desorption time were 70 min and 15 min, respectively; the pH value of sample matrix was 8.0; no salt was added in sample matrix. Under the optimal extraction conditions, the MMF/MAED-SPME showed expected extraction performance to BUs. It can be seen from Fig. S4b that the peak heights for the five BUs obviously increase after enrichment. The enriched factors (EF) (calculated by the ratio of the slopes of the calibration curves obtained with and without extraction) for HFU, TFU, LFU, FFU and CFU were 138, 179, 83, 74 and 53, respectively. The

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comparison of extraction performance of MMF/MAED-SPME, MMF/VIED-SPME and MMF/MAIED-SPME to BUs was also performed. It can be seen from the Fig.S4

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and the data in Table S2, under the same conditions, the MMF/MAED-SPME shows

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the best extract performance among the three MMFs. The comparison further demonstrates that the new MMF/MAED-SPME can enrich the BUs effectively.

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3.3. Validation of the MMF/MAED-SPME-LD-HPLC/DAD method

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Typically, linear dynamic range, correlation coefficients, recoveries, limits of

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detection (LODs), limits of quantification (LOQs), repeatability and reproducibility

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are main parameters for evaluating the validation of an analytical method [16-19]. In this work, linear dynamic range was constructed with the BUs spiked to the blank

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samples over the range of 0.10-200.0 μg L-1. Linear regression analyses were

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performed using relative peak areas against the respective analytes concentration. The

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results are listed in Table 2. The linear dynamic ranges for HFU and TFU in water sample were 0.10-200.0 μg L-1, and 0.25-200.0 μg L-1 for other BUs. The

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corresponding values in juice samples were 0.50-200.0 μg L-1 and 1.0-200.0 μg L-1, respectively. The all linear dynamic ranges possess good linearity (R2 > 0.99). The

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LOD and LOQ were determined at a concentration at which signal-to-noise ratios were equal to 3 and 10, respectively. For water samples, the LOD and LOQ were in the range of 0.026-0.075 μg L-1and 0.084-0.25 μg L-1, respectively. The corresponding values in juice samples were in the range of 0.053-0.29 μg L-1 and 0.17-0.96 μg L-1, respectively. The repeatability of proposed method was evaluated in terms of intra- and inter-day precision. Results showed that a satisfactory repeatability

was achieved, the relative standard deviations (RSD) for intra- and inter-day precision were less than 9% and 10%, respectively. At the same time, good reproducibility was obtained, the RSD less than 10% in all cases. These results demonstrate that the proposed method has good repeatability, reproducibility and high sensitivity for the detection of BUs, and can be used to routinely monitor BUs in water and juice samples. 3.4. Real samples analysis To further demonstrate the applicability of the proposed method, two

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environmental water samples and two juice samples were analyzed with MMF/MAED-SPME-LD-HPLC/DAD. Fig.6 shows the typical chromatograms of

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non-spiking and the spiking water and juice samples analyzed with present method. It

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can be seen from Fig.6 and data in Table 3 that low concentration of FFU and CFU were detected in river and farmland water samples. No target analyte was determined

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in the orange and grape juice samples. To further validate the feasibility of the

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proposed method, extraction recoveries were assessed by spiking water and juice

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samples with BUs at concentration levels of 1.0, 10.0 and 100.0 μg L-1 via the

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addition of standard solutions. The results in Table 3 show that the recoveries of the five BUs from the all samples are in the range from 65.1% to 118% with the RSDs

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method are acceptable.

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less than 10%, which demonstrates that the accuracy and precision of the present

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3.5. Comparison with previous methods A comparison of LODs achieved at present method and previous reported

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analytical methodologies for BUs in water and juice samples is summarized in Table 4. Typically, the determination of BUs with mass spectrum (MS) [23] and

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fluorescence detector (FLD) [11, 22] was more sensitive than using HPLC method with UV detection [5, 8-10, 14, 20, 21]. However, for the detection of the HFU and TFU in juice samples, the proposed method exhibited a greater sensitivity than SPME-HPLC/FLD [11]. It also can be seen from the comparison, for the detection of the HFU and TFU in water and juice samples, lower LOD could be obtained in the present method than other methods with the same kind of detector [5, 8-10, 14, 20,

21]. At the same time, for water samples, the LODs for BUs achieved at present method were lower than previous studies with UV detector [5, 10, 14, 19].

4. Conclusions In summary, a new SPME based on multiple monolithic fiber was successfully prepared using methacrylic acid and ethylene dimethacrylate as monomer and cross-linker, respectively. The MMF/MAED-SPME showed expected extraction performance for benzoylurea insecticides through multi-interactions such as hydrophobic and ion-exchange interactions. Under optimized conditions, the

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developed method of MMF/MAED-SPME-LD-HPLC/DAD was used to determine

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trace BUs in water and juice samples effectively. In comparison with the existing extraction methods for the monitoring of BUs, the proposed method was convenient,

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sensitive, cost-effective and environmentally friendly. Therefore, the proposed method may serve as a promising alternative to the monitoring of BUs in water, juice

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and other complicated samples.

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Acknowledgements

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The work described in this article was the supported by National Natural Science Foundation of China (grant: 21377105); Fundamental Research Funds for the Central

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Universities (grant: 20720140510); New Century Excellent Talents in Fujian Province

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University; Fundamental Innovation Research Funds for postgraduates in Xiamen

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University (201412G014).

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A

Magnetic retrieval of ionic liquids: Fast dispersive liquid-liquid microextraction

M

for the determination of benzoylurea insecticides in environmental water samples, J. Chromatogr. A 1254 (2012) 23-29.

D

[9] M.Y. Yang, P.J. Zhang, L. Hu, R.H. Lu, W.F. Zhou, Ionic liquid-assisted

TE

liquid-phase microextraction based on the solidification of floating organic

EP

droplets combined with high performance liquid chromatography for the determination of benzoylurea insecticide in fruit juice. J Chromatogr A, 1360

CC

(2014) 47-56.

A

[10] Y.R. Huang, Q.X. Zhou, G.H. Xie, H.J. Liu, H.Y. Lin, Titanium dioxide nanotubes

for

solid

phase

extraction

of benzoylurea

insecticides

in

environmental water samples, and determination by high performance liquid chromatography with UV detection, Microchim. Acta 172 (2011) 109-115.

[11] P.P. Vazquez, A.R. Mughari, M. M. Galera, Solid-phase microextraction for the determination of benzoylureas in orange juice using liquid chromatography

combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection, J Sep Sci. 31 (2008) 56-63. [12] M. Mei, X.J. Huang, D.X. Yuan, Multiple monolithic fiber solid-phase microextraction: A new extraction approach for aqueous samples, J. Chromatogr. A 1345 (2014) 29-36. [13] M. Mei, X.J. Huang, Y. Jie, D.X. Yuan, Sensitive monitoring of trace nitrophenols in water samples using multiple monolithic fiber solid phase microextraction and liquid chromatographic analysis, Talanta 134 (2015) 89-97.

dispersive

liquid-phase

microextraction

and

high

PT

[14] Q.X. Zhou, X.G. Zhang, Combination of ultrasound-assisted ionic liquid performance

liquid

RI

chromatography for the sensitive determination of benzoylureas pesticides in

SC

environmental water samples, J. Sep. Sci. 33 (2010) 3734-3740.

[15] H. Lord, J. Pawliszyn, Microextraction of drugs, J. Chromatogr. A 902 (2000)

U

17-63.

N

[16] M. Zarejousheghania, M. Möderb, H. Borsdorf, A new strategy for synthesis of

A

an in-tube molecularly imprinted polymer-solid phase microextraction device:

M

Selective off-line extraction of 4-nitrophenol as an example of priority pollutants from environmental water samples, Anal. Chim. Acta 798 (2013) 48-55.

D

[17] Y.L. Wang, J. Zhang, X.J. Huang, D.X. Yuan, Preparation of stir cake sorptive

TE

extraction based on polymeric ionic liquid for the enrichment of benzimidazole

EP

anthelmintics in water, honey and milk samples, Anal. Chim. Acta 840 (2014) 33-41.

CC

[18] Method validation and quality control procedure for pesticide residues analysis in food and feed, Document No. SANCO/10684/2009 from European Union.

A

[19] Determination of 450 pesticides and related chemicals residues in fruits and vegetables, Chinese National Standards GB/T 20769-2008.

[20] J.K. Zhou, R.Y. Liu, G. Song, and M.C. Zhang, Determination of Carbamate and Benzoylurea Insecticides in Peach Juice Drink by Floated Organic Drop Microextraction–High Performance Liquid Chromatography, Anal. Lett. 42 (2009) 1805-1819.

[21] C.H. Wang, X.X. Ma, C. Wang, Q.H. Wu, Z. Wang, Poly (vinylidene fluoride) membrane based thin film microextraction for enrichment of benzoylurea insecticides from water samples followed by their determination with HPLC, Chin. Chem. Lett. 25 (2014) 1625-1629. [22] M.D. Gil Garcia, M. Martinez Galera, D. Barranco Martinez, J. Gisbert Gallego, Determination of benzoylureas in ground water samples by fully automated on-line pre-concentration and liquid chromatography-fluorescence detection, J Chromatogr A 1103 (2006) 271-277.

PT

[23] D. Barranco Martinez, M. Martinez Galera, P. Parrilla Vazquez, M. Dolores Gil Garcia, Simple and Rapid Determination of Benzoylphenylurea Pesticides in

RI

River Water and Vegetables by LC–ESI-MS. Chromatographia, 66 (2007)

A

N

U

SC

533-538.

M

Figure Captions

Fig. 1 The photos of single thin monolithic fiber (a), MMF/MAED-SPME with four

D

thin fibers (b) and pore size distribution plot of poly (MA-co-ED) monolith (c).

TE

Fig. 2 The effect of desorption solvent on extraction performance. Conditions: extraction and desorption time were both 0.5 h; no salt was added in

EP

the sample and the pH values of sample matrix were not adjusted. The spiked

CC

concentration was 100 μg L-1 for each BUs. Symbols: HFU; TFU;  LFU; FFU;  CFU.

A

Fig. 3 The effect of extraction time on extraction performance. (a) MMF/MAED-SPME; (b) thick fiber Conditions: methanol was used as desorption solvent; desorption time was 0.5 h. The other extraction parameters and symbols were the same as in Fig.2. Fig. 4 The effect of pH value of sample matrix on extraction performance. Conditions: extraction and desorption time were 70 and 15 min, respectively; the

sample pH values were adjusted by 0.1 mol L-1 HCl or 0.1 mol L-1 NaOH. The other conditions and symbols were the same as in Fig.2. Fig. 5 The effect of salt concentration in sample matrix on extraction performance. Conditions: pH value of sample matrix was adjusted to 8.0. The other conditions and symbols are the same as in Fig.4. Fig. 6 Typical HPLC chromatograms of five BUs. (a) Direct injection of spiking water or orange juice sample; (b) Spiking water or orange juice samples with each analyte at 100.0 μgL-1 and

PT

treated with MMF/MAED-SPME. Conditions: methanol was used as desorption solvent; extraction and desorption

RI

time were 70 and 15 min, respectively; the pH value of sample matrix was 8.0;

SC

no salt was added in sample matrices. The spiked concentration was 100.0 μgL-1

A

CC

EP

TE

D

M

A

N

U

for each BUs.

SC RI PT

Table 1. Extraction efficiency of different MMF/MAED for BUs Monomer mixture EDMA (%, w/w)

Monomer mixture (%, w/w)

1

10

90

45

55

2.69

3.18

1.24

1.36

0.92

2

15

85

45

55

1.53

1.78

0.73

0.80

0.62

3

20

80

45

55

1.54

1.81

0.69

0.77

0.53

4

25

75

45

55

1.98

2.00

1.06

1.20

0.97

5

30

70

45

55

3.33

3.38

1.55

1.75

1.14

6

35

65

45

55

1.60

1.56

0.81

0.95

0.76

7

40

60

45

55

1.76

1.55

1.01

1.16

1.02

8

45

55

45

55

1.65

1.36

0.86

0.99

0.80

N

M D

TE

EP

HFU

TFU

LFU

FFU

CFU

9

30

70

40

60

2.31

2.35

1.21

1.34

0.99

10

30

70

50

50

2.52

2.42

1.24

1.42

1.05

A

CC

Porogen solvent (%, w/w)

U

MA (%, w/w)

A

NO

Peak area (×104)

Polymerization mixture

11

30

70

55

45

2.82

3.07

1.30

1.44

1.06

12

30

70

60

40

2.49

2.23

1.33

1.50

1.23

Note: the sample matrix was ultrapure water and the spiked concentration for each compound was 100 μg L-1.

SC RI PT

Water

HFU

D

TFU LFU FFU

A

Compounds

Linear range a (μg L-1)

CC

0.10-200.0 0.25-200.0 0.25-200.0

CFU HFU

0.25-200.0 0.50-200.0

TFU LFU FFU

0.50-200.0 1.00-200.0 1.00-200.0

CFU

1.00-200.0

TE

EP

Juice

0.10-200.0

M

Samples

N

U

Table 2 Linear dynamic range, correlation coefficients, LODs and LOQs, inter-day and intra-day precisions, reproducibility achieved for the five BUs

b

c

R2

LOD (μg L-1)

LOQ (μg L-1)

0.9912 0.9930 0.9908

0.026

0.084

0.030 0.071 0.068

0.10 0.24 0.22

0.075 0.072

0.25 0.24

0.053 0.28 0.24

0.17 0.94 0.81

0.9902 0.9925 0.9920 0.9960 0.9935 0.9968 0.9922

0.29

0.96 -1

a: Spiking level included 0.10, 0.25, 0.50, 1.00, 5.00, 10.0, 20.0, 50.0 , 100.0 and 200.0 μg L , respectively.

A

b: S/N=3;

c: S/N=10; d: Assays at 100.0 μg L-1 level.

Intra-day precision d (RSD%; n=4)

Inter-day precision d (RSD%; n=4)

4.47 7.17 6.00

6.60 4.56 8.23

4.99 7.49 2.17 5.14 5.95 6.72 8.68

8.48 9.59 8.35 4.89 8.60 9.36 6.50

Reproducibility d (RSD%; n=4) 7.41 8.49 7.80 7.18 8.10 8.90 9.58 7.10 8.48 7.09

SC RI PT

Table 3. Results of determination and recoveries of real water and juice samples spiked with five BUs Detected (μg L-1)/recoveries (%RSD, n=3)

-1

Samples

Spiked (μg L )

River water

0 1

ND 0.96

10

7.76 72.45

A

CC

Grape juice

ND; not detected.

U N

A

72.5 (6.5)

0.69 6.76 68.5

ND 1.01 7.33 70.9

TFU

101 (8.4) 73.3 (8.8) 70.9 (5.1)

ND

69.0 (6.6) 67.6 (4.2) 68.5 (5.0)

0.76 6.56 65.5

68.1 (7.7)

ND 0.79

ND 0.94 9.20 101

LFU 93.6 (9.4) 92.0 (8.9) 101 (7.1)

ND 76.3 (6.6) 65.6 (0.8) 65.5 (7.6)

0.65 6.94 94.1

78.8 (9.2)

ND 0.93

FFU 0.92 1.73 11.3 95.1

81.0 (6.3) 104 (9.8) 94.2 (9.1)

0.36 65.4 (9.4) 69.4 (5.4） 94.1 (3.0)

1.20 9.47 87.8

92.8 (6.3)

ND 0.90

CFU 0.84 1.85 12.6 117

101 (6.5) 118 (8.6) 116 (9.4)

0.81 84.2 (7.6) 91.1 (9.8) 87.4 (3.2)

1.90 10.0 98.8

109 (8.5) 92.0 (7.7) 98.0 (8.4)

89.5 (7.2)

ND 0.70

69.5 (7.7)

0 1

ND 0.68

10 100 0

8.98 65.1 ND

89.8 (9.2) 65.1 (9.7)

10.3 79.1 ND

103 (7.8) 79.1 (8.8)

8.41 69.7 ND

84.1 (1.0) 69.7 (7.0)

6.65 66.7 ND

66.5 (9.2) 66.7 (8.4)

6.58 69.5 ND

65.8 (3.2) 69.5 (3.0)

1

1.05

105 (7.0)

1.02

102 (8.2)

1.15

115 (6.4)

0.69

68.8 (5.8)

0.65

65.2 (5.6)

10

11.3

113 (1.8)

10.7

107 (9.4)

10.7

107 (4.3)

9.86

98.6 (5.5）

8.39

83.9 (7.7)

100

114

114 (5.4)

99.7

99.7 (8.7)

103

103 (5.8)

102

102 (6.3)

88.0

88.0 (2.2)

EP

Orange juice

77.6 (7.9)

ND

TE

1 10 100

95.6 (1.5)

M

Farmland water

D

100 0

HFU

SC RI PT

Table 4. Comparison of the limits of detection of present method with other methods

TE

EP

MMF-SPME/DAD

HFU

TFU

LFU

/ 10.0 0.10 / / / 0.10 0.07 / / 0.030 0.053

0.10 / 0.15 / / / / / 0.02 0.0075 0.071 0.28

0.23 5.0 0.056 / / / 0.10 0.10 0.02 0.0057 0.026 0.072

A

FFU

CFU

0.05 / 0.11 0.21 0.21 0.63 / 0.15 0.02 0.0035 0.068 0.24

0.03 / / 0.19 0.21 0.82 / 0.05 / / 0.075 0.29

a. ionic liquid-assisted liquid-liquid microextraction based on the solidification of floating organic droplets. b. floated organic drop microextraction. c. dispersive liquid-phase microextraction. d. thin-film microextraction. e. ionic liquid dispersive liquid-liquid microextraction technique combined with magnetic retrieval.

CC A

juice juice juice water water water water water water water water juice

M

D

ILSFOD-LLMEa-HPLC/UV FDMEb-HPLC/UV SPME-HPLC/FLD SPE-HPLC/UV DLPMEc-HPLC/UV DLPME-HPLC/UV TFMEd-HPLC/UV MR-IL-DLLMEe-HPLC/UV SPE-HPLC/FLD SPE-LC/ MS

LOD (μg L-1 or μg kg-1)

U

Sample

N

Method

Ref. [9] [20] [11] [10] [14] [5] [21 [8] [22] [23] Present study

D

TE

EP

CC

A

A

M

N

U

SC RI PT

D

TE

EP

CC

A

A

M

N

U

SC RI PT

D

TE

EP

CC

A

A

M

N

U

SC RI PT

D

TE

EP

CC

A

A

M

N

U

SC RI PT

D

TE

EP

CC

A

A

M

N

U

SC RI PT

D

TE

EP

CC

A

A

M

N

U

SC RI PT