New magnetic solid phase extractor based on ionic liquid modified β-cyclodextrin polymer/Fe3O4 nanocomposites for selective separation and determination of linuron
© Bakheet et al. 2016
Received: 3 October 2015
Accepted: 11 January 2016
Published: 26 January 2016
Direct determination of trace analyte, in particular at ultra-trace concentration, cannot be easily achieved in complex systems by UV-visible spectrometry because of the lack of sensitivity and selectivity of the method. Therefore, an efficient separation step is often required prior to the determination. In accordance, a new magnetic solid phase extractor based on ionic liquid modified carboxymethyl-hydroxypropyl-β-cyclodextrin polymer magnetic particles Fe3O4 functionalized with ionic liquid (IL-CM-HP-β-CDCP magnetic nanoparticles (MNPs)) was developed for a selective separation of linuron prior to its determination by UV-visible spectrometry.
Ionic liquid modified carboxymethyl-hydroxypropyl-β-cyclodextrin polymer magnetic particles Fe3O4 (Fe3O4@IL-CM-HP-β-CDCP) were confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray powder diffraction (XRD). The uptake behavior of the new Fe3O4@IL-CM-HP-β-CDCP MNPs adsorbent toward linuron was studied. The concentrations of linuron were directly determined after reading absorbance by UV-visible spectrometry.
Fourier transform infrared spectroscopy, scanning electron microscopy, and XRD results strongly confirmed the formation of Fe3O4@IL-CM-HP-β-CDCP MNPs phase. Adsorption study revealed the Fe3O4@IL-CM-HP-β-CDCP MNPs for a selective separation of linuron prior to its determination by UV-visible spectrometry. The results showed that linuron was adsorbed rapidly on Fe3O4@IL-CM-HP-β-CDCP MNPs and eluted by 4.0 mL ethanol in 15 min. Under the optimized conditions, the linear calibration curves for linuron were obtained over the concentration range of 0.07–19.00 μg mL−1 with a relative standard deviation of 1.97 % (n = 3, c = 4.00 μg mL−1). The detection limits, the limit of quantification, correlation coefficient (R), and preconcentration factor were 7.0 μg L−1, 70.0 μg L−1, 0.9987, and 15, respectively.
Ultimately, the developed method can be applied and effectively utilized for the determination of linuron in real samples.
Various methods have been developed for the determination of linuron to date, including HPLC (Katsumata et al. 2007), electrochemical method (Lima et al. 2011), HPLC-MS (Petrovic et al. 2010), sensor method (Ciumasu et al. 2005), capillary electrophoresis (Da Silva et al. 2003), and UV spectrometry (Chen and Zhu 2015). UV spectrometry has many advantages including simple operation, lower cost, and repeatable results. However, the direct determination with spectrophotometry for linuron is difficult owing to matrix effects and its lower concentration in natural samples. So, UV spectrometry is often combined with separation/enrichment technique to improve the selectivity and sensitivity of detection (Chen and Zhu 2015).
Magnetic solid phase extraction (MSPE) is a kind of magnetic or magnetizable material as absorbent matrix solid phase extraction technique (Giakisikli and Anthemidis 2013), which has many advantages including simple operation, short extraction time, low organic solvent consumption, and easy automation. It has a broad application prospect in detection analysis (Jiang et al. 2013). To date, MSPE extraction agent is mainly Fe3O4 nanoparticles (NPs) with specific chemical functional group modified on the surface to achieve concentration of the targeted analytes. Numerous organic polymers and inorganic polymers have been used to modify Fe3O4 NPs. The unique structures of cyclodextrins (CDs), which have a cavity possessing a hydrophilic external surface and a hydrophobic internal surface, make them useful in separation processes. β-CDCP by polymerizing cyclodextrin with epichlorohydrin was a spherical or grainy solid subject and insoluble in water, which still retained the inclusion property of β-CD, was synthesized by the reaction of β-CD and cross-linked agent. β-CDCP as a solid phase extraction material had been applied to selectively separation/preconcentration the similar size of materials (Zhu and Ping 2014). Yu et al. modified the Fe3O4 NPs with hydroxypropyl-β-cyclodextrin (HP-β-CD) and polyethyleneglycol 400 (PEG400) for the removal of congo red from aqueous solutions (Yu et al. 2014). The related research by our group indicated (1) Fe3O4@cyclodextrin polymer NPs (Fe3O4@β-CDCP) as adsorbents for preconcentration/extraction of rutin from lotus plumule (Gong et al. 2014) and (2) self-assembly Fe3O4@SiO2@ILs as adsorbents for preconcentration/extraction of linuron (Chen and Zhu 2015). But, there was no report to separation/analysis linuron with Fe3O4@IL-CM-HP-β-CDCP magnetic nanoparticles (MNPs).
In this study, carboxymethyl-hydroxypropyl-β-cyclodextrin polymer magnetic particles Fe3O4 (Fe3O4@CM-HP-β-CDCP) which has a good hydrophobic and stability properties were prepared and modified with ionic liquid (Fe3O4@IL-CM-HP-β-CDCP). The magnetic solid phase extraction followed by UV-vis spectroscopy was applied to separation/analysis linuron in real samples with reasonable results. Compared with the previously reported works, (1) this adsorbent-based MSPE provides a rapid and efficient sample preparation process, which enables the treatment of large volume samples in a short period of time (Gong et al. 2014; Cheng et al. 2012) and (2) the adsorbent Fe3O4@IL-CM-HP-β-CDCP MNPs could be used repeatedly and better preconcentration factor (Chen and Zhu 2015).
Materials and reagents
Fourier transform infrared spectroscopy (FTIR) spectra were measured with a Bruker Tensor 27 spectrometer (Bruker Company, Germany). Samples were pressed into KBr pellets and recorded at the frequencies from 4000 to 400 cm−1 with resolution of 4 cm−1. A SEM Hitachi S-4800 II instrument was used to obtain micrographs of the material. UV-2500 spectrophotometer (Shimadzu Corporation, Japan) was used. Neodymium magnet and timing multifunctional oscillator (Guohua Limited Company, China), a digital water-bath (Guohua Limited Company, China), and pH meter (Shanghai Jinke Limited Company, China) were used.
All chemicals and reagents were at least of analytical reagent grade, unless otherwise stated, as follows: N-methylimidazole (Darui Fine Chemicals, Shanghai, China), 1-bromooctane (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), KPF6, FeCl3, FeSO4 · 7H2O, acetone, methylene chloride, NaOH, HCl, carbinol, ethanol, sodium dodecyl sulfate (SDS), acetonitrile (ACN), hydroxypropyl-β-cyclodextrin, and epichlorohydrin (Shanghai Chemical Reagent Corporation, China). Linuron standards were obtained from the Sigma-Aldrich (Shanghai, China). A standard stock solution was prepared by dissolving 10.0 mg of each standard in 100 mL of ethanol and stored in dark at 4 °C. Working standard solutions were obtained by appropriate dilution of the stock solution.
Synthesis of Fe3O4@IL-CM-HP-β-CDCP MNPs
Synthesis of CM-HP-β-CDCP MNPs
CM-HP-β-CDCP MNPs were prepared according to literature (Badruddoza et al. 2013).
Synthesis of Fe3O4@IL-CM-HP-β-CDCP MNPs
[C8MIM][PF6] was synthesized according to literature (Zhao et al. 2007). Then, 5 g of CM-HP-β-CD polymer was stirred for 3 days in 20 mL of [C8MIM][PF6] medium for effective impregnation. The adsorbent was dried at 90 °C for 3 days. Then, the product was dried at 90 °C for 24 h and sonicated for 1 day again, and the resulting polymer was Fe3O4@IL-CM-HP-β-CDCP MNPs.
Water sample: Lake water was collected from the Slender West Lake in Yangzhou, China. A 50.0 mL of lake water sample was filtered through a 0.45-μm membrane to remove suspended particles before analysis.
Fruit and vegetable samples (Farokhcheh and Alizadeh 2013): Apple and lettuce samples were supplied by our local market. A 20.0 g of apple (or lettuce) slurry and 20 mL anhydrous ethanol were placed in a 50-mL centrifuge, and the mixture was then shaken for 20 min. After centrifugation, the upper fluids in the tube were filtered and collected in a volumetric flask.
Procedure of adsorption and elution
A 40.0 mL of the working solution or aqueous sample and 0.10 g of Fe3O4@IL-CM-HP-β-CDCP MNPs were transferred into a centrifuge tube, and the solution in the tube was subsequently shaken in the constant temperature shaking table for 20 min at room temperature. Then, Fe3O4@IL-CM-HP-β-CDCP MNPs with adsorbed target linuron was separated from the solution by an external magnetic field. The residual linuron in the supernatants was determined by UV-vis spectroscopy at 246 nm.
In the adsorption of linuron Fe3O4@IL-CM-HP-β-CDCP MNPs with 4.0 mL ethanol ultrasound elution for 20 min, eluent were determined by the UV-vis spectroscopy.
Determination of inclusion constant
The procedure of the determination of inclusion constant was based on the literature (Zhou et al. 2013).
Results and discussion
Characterization of Fe3O4@CM-HP-β-CDCP MNPs
Characterization by FTIR
Characterization by SEM
Characterization by XRD
Optimization of adsorption
Effect of pH
Effect of adsorption temperature
The effect of temperature (10.0 °C 50.0 °C) on the adsorption efficiency of linuron was tested. Linuron could effectively be absorbed on the Fe3O4@IL-CM-HP-β-CDCP MNPs in the range of 20–40 °C; herein, the adsorption of the analyte was conveniently carried out at room temperature.
Effect of adsorption time
The effect of adsorption time on the adsorption efficiency was carefully studied in the range from 5–60 min. The results illustrated that adsorption efficiency of linuron finished after 20 min and stabled. Thereafter, 20 min of extraction time was performed for further study.
Effect of sample volume
where C o and C e are the initial and equilibrium concentration of linuron (μg mL−1), m is the weight of Fe3O4@IL-CM-HP-β-CDCP (g), and V is the volume of solution (mL).
Optimization of elution
Selection of eluent
Effect of elution temperature
The elution efficiency of linuron at different temperatures (10–50 °C) was studied. The elution efficiency increased progressively with the temperature from 5 to 20 °C. And, the elution efficiency of linuron was greater than 85.0 % and remained constant at the elution temperature ranging from 20 to 40 °C. Accordingly, the elution was performed at room temperature.
Effect of elution time
The effect of elution time on the elution of linuron was also estimated. The elution efficiency of linuron became stable after 15 min. Thereafter, 15 min of elution time was selected for further studies.
Effect of eluent volume
Reuse of Fe3O4@IL-CM-HP-β-CDCP MNPs
Effect of interference
Tolerance of interference ions
Tolerance ratio in mass (w/w) (tested substances to analyte ratio)
Fe3+, NO3 −, SO4 2−
Carbendazim, benomyl, acetamiprid
Analytical performance of the method
Once optimized, the method was finally characterized in terms of linearity, precision, accuracy, and sensitivity. Under the optimum conditions, the matrix matching calibration curve of noninterference was established with standard addition method in the concentration range of 0.07–19.0 μg mL−1. The equation of calibration graph was A = 0.231c + 0.057 (μg mL−1), with a correlation coefficient of 0.9987. The limit of detection, defined as LOD = 3 σ/k (where σ is the standard deviation of blank and k is the slope of calibration graph) was 7.0 μg L−1. The limit of quantification was 70.0 μg L−1. The precision (relative standard deviation) was 1.97 % (n = 3, c = 4.00 μg mL−1). The preconcentration factor, defined as the quotient of volume before absorption and after elution, was 15-fold.
The recoveries of linuron in samples (n = 3)
Comparison with other methods
Comparison with the results in other literatures
Discussion of extraction mechanism
The inclusion constant K is a significant parameter which illustrates inclusion interactions of host-guest molecules. The inclusion complex can be easily formed at a higher K. The inclusion constants of the monomers of two kinds of polymers (CM-HP-β-CD and IL-CM-HP-β-CD) and linuron were measured. The form of inclusion and the inclusion constant can be calculated by UV-visible absorption spectroscopy and Hildebrr and Benesi equation (Zhao et al. 2007).
Fe3O4@IL-CM-HP-β-CDCP MNPs used as a solid phase extraction material to preconcentrate/separate linuron coupled with UV for the analysis of linuron is established. The proposed method has some advantages, such as easy, safe, and inexpensive methodology for the separation/determination of linuron in fruit and vegetable samples.
The authors acknowledge the financial support from the National Natural Science Foundation of China (21375117) and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
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