научная статья по теме MAGNETIC MOLECULARLY IMPRINTED POLYMER NANOPARTICLES FOR SELECTIVE EXTRACTION OF COPPER FROM AQUEOUS SOLUTIONS PRIOR TO ITS FLAME ATOMIC ABSORPTION DETERMINATION Химия

Текст научной статьи на тему «MAGNETIC MOLECULARLY IMPRINTED POLYMER NANOPARTICLES FOR SELECTIVE EXTRACTION OF COPPER FROM AQUEOUS SOLUTIONS PRIOR TO ITS FLAME ATOMIC ABSORPTION DETERMINATION»

ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2015, том 70, № 11, с. 1162-1166

ОРИГИНАЛЬНЫЕ СТАТЬИ

УДК 543

MAGNETIC MOLECULARLY IMPRINTED POLYMER NANOPARTICLES FOR SELECTIVE EXTRACTION OF COPPER FROM AQUEOUS SOLUTIONS PRIOR TO ITS FLAME ATOMIC ABSORPTION DETERMINATION

© 2015 Massoud Kaykhaii*, 1, Mostafa Khajeh**, Sayyed Hossain Hashemi***

*Department of Chemistry, Faculty of Sciences, University of Sistan and Baluchestan University Boulevard, Zahedan 98135-674, Iran

1E-mail: kaykhaii@chem.usb.ac.ir **Department of Chemistry, University of Zabol Zabol, Iran

***Department of Marine Chemistry, Faculty of Marine Science, Chabahar Maritime University Chabahar, Iran Received 27.07.2014; in final form 14.04.2015

This paper describes a pre-concentration procedure using magnetic molecularly imprinted polymer (MMIP) nanoparticles for the extraction of copper(II) from aqueous samples prior to its atomic absorption determination. Cu—morin complex was used as template molecule which was chemically bonded to MMIP nanoparticles. MMIP nanoparticles were characterized by scanning electron microscopy as well as Fourier transform infrared spectroscopy. The extraction conditions including pH value, adsorption and desorption time, temperature, amount of ligand and ionic strength of the sample matrix were studied and optimized. The method showed good extraction recoveries (>96%) with relative standard deviation below 3.4% for real samples. The linear range of calibration curve was between 5—1000 p.g/L with a correlation coefficient (r2) of 0.996. The detection limit was 0.5 p.g/L. The method was suitable for the determination of trace copper in drinking water samples.

Keywords: magnetic molecularly imprinted polymer nanoparticles, copper determination, trace analysis. DOI: 10.7868/S0044450215110110

Copper is an essential element for the catalytic activity of many enzymes [1]. It is also required to maintain the normal structure, function, and proliferation of living cells [2]. While a slight quantity of copper is essential for normal physiological processes, copper in excess of the recommended dosage may pose a threat to human health. The effect of excessively ingested copper includes salivation, epigastria pain, nausea, vomiting, diarrhea, intravascular hemolytic anemia, acute hepatic and renal failure, shock, and coma [3]. The maximum tolerable daily intake for copper is 0.5 mg/kg of body weight [4]. So, it is very important to efficiently detect the concentration ofcopper in environmental water samples. Determination of very low concentrations of trace elements including copper generally requires separation and pre-concentration steps [5].

Using nano-size magnetic particles is attracting significant interest because of their great potential in bio-affinity applications including immunoassays, magnetic resonance imaging as contrast agents and drug delivery vehicles [6]. The magnetic iron oxide nanoparticles can be easily isolated from a matrix by

applying a magnetic field without retaining residual magnetism after removal of the field. However, uncoated super magnetic nanoparticles have some limitations and a surface modification is necessary in order to: i) stabilize the colloid dispersion; ii) ensure specific compatibility to avoid undesirable interactions; and iii) provide functional groups for further derivatizations [7]. If super magnetic nanoparticles are coated with a molecularly imprinted polymer (MIP) layer, specific molecular recognition can be combined with magnetic properties [8]. When MIP particles contain magnetic components, such as iron oxide, they should be easily separated by external magnetic fields after extraction and recognition.

We tried to develop a simple, quick and sensitive method for extraction and determination of copper in water samples using magnetic polymer particles. Since there are only few publications concerning the use of magnetic molecularly imprinted polymer nanoparti-cles for metal ion extraction, it was also interesting to develop a method for such applications.

EXPERIMENTAL

Reagents and materials. 4-Vinylpyridine (VP), ethyleneglycol dimethacrylate (EDMA) and 2,2' azo-bisisobutyronitrile (AIBN) were obtained from Sigma-Aldrich (Milwaukee, WI, USA). Reagent grade CuSO4 ■ 5H2O, FeCl2 ■ 4H2O, FeCl3 ■ 6H2O and nitrate or chloride salts of other cations (all from Merck, Darmstadt, Germany) were of the highest purity available and used without further purification. All acids used were of the analytical grade from Merck. Reagent grade morin (3,5,7,2',4'-pentahydroxyflavone) was used as received. A stock solution of copper (1000 mg/L) was prepared by dissolving a proper amount of copper sulfate in doubly distilled water in a 50-mL measuring flask and diluting to the mark with doubly distilled water. Work solutions were prepared daily by appropriate dilution of stock solution.

Apparatus. A Konik Won M300 (Barcelona, Spain) flame atomic absorption spectrometer (FAAS) was employed for determination of copper concentration. The most sensitive wavelength for copper at 324.8 nm was applied with bandwidths of 1.2 nm. The pH was determined with a model 630 Metrohm (Switzerland) pH meter with combined glass-calomel electrode. The Fourier transform infrared (FTIR) spectrometer TENSOR 27 (Bruker, Germany) was applied to investigate the composition of the MMIP nanoparticles. A VEGA II TESCAN scanning electron microscope (Check Republic) was used to investigate the coating surface.

Preparation of iron oxide magnetic nanoparticles.

Magnetic nanoparticles were prepared by co-precipitation of Fe(II) and Fe(III) ions by a solution of ammonia and treating under hydrothermal condition [9]. The FeCl3 • 6H2O and FeCl2 ■ 4H2O (molar ratio of 2 : 1) were dissolved in water at a concentration of 0.3 M iron ions. The chemical precipitation was achieved at 25 °C under vigorous stirring by adding ammonia solution (29.6%). During the process of reaction, the pH was maintained at approximately 10.5. The precipitates were heated at 70°C for 35 min to eliminate residual solvent, and then were washed repeatedly with distilled water and ethanol. Finally, they were dried in a vacuum oven at 65° C.

Preparation of the MIPs with magnetic susceptibility. A novel molecularly imprinted polymer coated magnetic nanoparticles for Cu—morin was prepared in a sealed polymerization reactor (100 mL volume) equipped with a temperature control system. Pre-polymer solution for molecularly imprinted polymer was prepared with 0.24 g of CuSO4 ■ 5H2O and 0.20 g of morin dissolved in 15 ml of methanol. Then 0.40 g of VP, 3.8 mL of EGDMA, 50 mg of AIBN and 0.50 g magnetite particles were added and deoxygenized with a nitrogen stream for 5 min. Then, the sealed reactor was placed in a water bath and polymerization was performed for 11 h at 65°C. The reactor content was stirred during polymerization. After completion of the

+ CUSO4, morin,

AIBN

Magnetic MIP nanoparticles unleached

CH3OH, EGDMA Polymerization Magnetic nanoparticles

ï\

Ä

ctq,

CtD.

I

cio = Template Cu-morin complex

ОrсЦО*° Magnetic MIP nanoparticles leached

Fig. 1. Schematic diagram of the preparation of magnetic molecularly imprinted polymer nanoparticles using Cu-morin as template molecule.

polymerization period, the reactor content was cooled down to room temperature. This polymerization led to the formation of brown MIP coated magnetic nanoparticles. The synthesized nanoparticles were ground, dried and sieved to get particles with diameters in the range of nm, dispersed in 10 mL of methanol and centri-fUged again. In order to remove the unreacted compounds, the MMIP nanoparticles were rinsed several times with methanol [10]. New MIP coated magnetic nanoparticles were rinsed several times by acetic acid solution to remove the template molecule. Figure 1 shows the schematic diagram of how the MIP coating can be covalently attached to the magnetic nanoparticles, and in Fig. 2 the scanning electron micrographs of the surface structure of MMIP nanoparticles are shown.

MIP coated magnetic nanoparticles extraction procedure. In a typical assay, the MMIP nanoparticles were immersed in 25 mL aqueous solution of Cu(II) (pH 5.5) and stirred for 20 min. After extraction, the MMIP nanoparticles were separated under a strong magnetic field. Desorption was carried out in 10 mL of concentrated CH3COOH by shaking the conical flask for 30 min. Then the MMIP particles were separated from solution under the same magnetic field. The elu-ents were evaporated close to dryness, and then 1 mL of 1 M HNO3 was added. Finally the concentration of free Cu(II) in solution was measured by FAAS. Three replicate extractions and measurements were performed for each concentration. The instrument response was periodically checked with known copper standard solutions.

RESULTS AND DISCUSSION

Infrared spectra. The infrared (IR) spectra of leached and unleached copper-imprinted MMIP nanoparticles (Fig. 3) were recorded using KBr pellet method. As can be seen, no absorption band is present

Elution with CH3COOH

1164 MASSOUD KAYKHAII и др.

(a) (b)

Fig. 2. Scanning electron micrographs of the magnetic molecularly imprinted polymer nanoparticles with a magnification of 28000 (a) and 50000 (b).

80

70

60

50

40

(a)

3500 3000 2500 2000 1500 Wavenumber, cm-1

(b)

1000 500

80

70 -

60 -

50

40

3500 3000 2500 2000 1500 Wavenumber, cm-1

1000 500

Fig. 3. FTIR spectra of leached (a) and unleached (b) magnetic molecularly imprinted polymer nanoparticles.

in the region of 1638—1648 cm-1, which confirms the absence ofvinyl groups in the MMIP nanoparticles. This shows the complete polymerization of vinyl pyridine. Meanwhile, there is other distinct difference between the IR spectra of the leached and unleached MMIP nanoparticles: the Cu stretching mode at 717 cm-1 disappeared in the leached MMIP nanoparticles.

Optimization of the MMIP nano-particles for cop-per(II) extraction. In order to optimize t

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