научная статья по теме HIGHLY SELECTIVE SOLID PHASE EXTRACTION OF MERCURY ION BASED ON NOVEL ION IMPRINTED POLYMER AND ITS APPLICATION TO WATER AND FISH SAMPLES Химия

Текст научной статьи на тему «HIGHLY SELECTIVE SOLID PHASE EXTRACTION OF MERCURY ION BASED ON NOVEL ION IMPRINTED POLYMER AND ITS APPLICATION TO WATER AND FISH SAMPLES»

ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2015, том 70, № 1, с. 7-14

ОРИГИНАЛЬНЫЕ СТАТЬИ

УДК 543

HIGHLY SELECTIVE SOLID PHASE EXTRACTION OF MERCURY ION BASED ON NOVEL ION IMPRINTED POLYMER AND ITS APPLICATION

TO WATER AND FISH SAMPLES © 2015 Majid Soleimani1, Majid Ghahraman Afshar

Department of Chemistry, Imam Khomeini International University (IKIU) P.O. Box: 288, Qazvin, Iran 1E-mail: m-soleimani@hotmail.com Received 24.12.2012; in final form 28.12.2013

A novel ion imprinted polymer (IIP) material has been synthesized for mercury ion. The IIP material is applied to the solid phase extraction (SPE) of Hg2+ from complex matrixes including water and fish samples. The IIP—SPE method is operated prior to cold vapor atomic absorption spectroscopy (CV—AAS) to determine mercury ion. In the polymer synthesis, mercury ion, 2-vinylpyridine, ethyleneglycol dimethacrylate and 2,2'-azo-bisisobutyronitrile are used as target, Hg2+ complexing reagent monomer, cross-linker and initiator, respectively. The polymer is characterized on the basis of FT-IR and thermal analysis (thermogravimetric, TGA; differential thermic, DTA; and differential scanning calorimetry, DSC). The obtained polymer block is ground, sieved and Hg2+ ions are removed from polymer particles by leaching with EDTA, which leaves a cavity in the polymer particles. The maximum Hg2+ adsorption capacity of IIP is 24.6 mg/g. Effective parameters on retaining Hg2+ such as pH, flow rate of sample and eluent, nature of the eluent, ionic strength, selectivity coefficient and retention capacity are investigated . The detection limit and the relative standard deviation are 5 x 10-4 ng/mL and 2.4%, respectively. After 20 adsorption cycles, the recovery of Hg2+ on IIP is only decreased by 3.2%. The column selective adsorption experiments of Na+, Cu2+, Pb2+, Cd2+, Ca2+ and Mg2+ ions with respect to mercury are conducted by using imprinted and non-imprinted polymer. These results showed that the IIP is highly selective for Hg2+ over the other metals.

Keywords: ion imprinted polymer, solid phase extraction, mercury ion, fish sample.

DOI: 10.7868/S004445021501020X

Heavy metal ion contamination represents a significant threat to the ecosystem and especially to people due to their severe toxicological effects on living or-ganisms[1, 2]. Inorganic and organic mercury compounds have been considered as a human health hazard because of their neurological damages, paralysis, chromosome breakage, kidney toxicity and birth defects [3—5] The safe amounts ofinorganic Hg2+ in drinking and industrial waste waters are 1.0 and 0.05 ^g/mL, respectively [6—8]. There are several analytical methods for the determination of mercury at low concentrations in environmental and biological samples [5, 9—17]. Modern analytical methods often fail to determine elements in environmental samples and biological materials, because of their limitations such as inadequate detection limits and interference from various species, which makes direct determination impossible.

SPE is replacing liquid—liquid extraction as a new technique for the preconcentration and interferences removal [9, 10, 18, 19]. A number of SPE advantages are: (i) higher enrichment factors, (ii) absence of emulsions, (iii) safety with respect to hazardous samples, (iv) mini-

mal costs due to low consumption of reagents, (v) flexibility, and (vi) easy incorporation into automated analytical techniques. Hence, many of today's researches, in selecting sorbents in SPE is based on using ion imprinted polymers and molecularly imprinted polymers because of their low price, stability in different environments and their higher selectivity than the other common solid sorbents such as immobilized naphthalene, cellulose, C18 bonded silica membrane discs, silica gel, glass beads, silica frit, metal hydroxides, activated carbon and functionalized polymer supports for preconcentrating and separating trace and ultratrace metal ions [15, 16, 20—23].

Ion imprinting technology is a strategy to produce chemically selective binding sites which recognize a particular ion in a macroporous polymer matrix [5, 24—27]. Ion recognition-based separation techniques have received much attention in various fields because of their high selectivity for target ions [22, 28, 29]. In ion-imprinting process, the selectivity of a polymeric adsorbent is based on the coordination geometry, coordination number of the ions, their charges and sizes.

Different approaches have been reported so far for metal ion imprinted resins, but no studies were reported concerning mercury ion removal from complex matrixes using ion-imprinted materials [5, 27, 29—31].

In this work, IIP materials were synthesized for mercury ion uptake. The obtained polymer block is ground, sieved and Hg2+ ions were removed from polymer particles. The polymer is characterized on the basis of FT-IR and thermal analysis (TGA, DTA and DSC). IIPs were applied as sorbents in SPE to separate and preconcentrate Hg2+ from complex matrixes. Effective parameters on extracting Hg2+ such as pH, flow rate of sample and eluent, nature of eluent, ionic strength and selectivity coefficient and retention capacity were investigated.

EXPERIMENTAL

Reagents and materials. EDTA, vinylpyridine (VP), ethylene glycol dimethacrylate (EGDMA), 2,2'-azobisisobutyronitrile (AIBN), methanol (HPLC grade), ethanol, propanol, HgCl, Cu(NO3)2 • 4H2O, Pb(NO3)2, Cd(NO3)2 • 4H2O, Ca(NO3)2 • 4H2O, MgCl2 • 6H2O, NaCl, NaOH, HCl (35%), HNO3 (65%) and thiourea were purchased in the highest quality available from Merck AG (Darmstadt, Germany). Stock solutions of Hg2+ (1000 ^g/mL) were prepared by dissolving appropriate amount of HgCl in double distilled water.

Apparatus. A B2000 pH meter equipped with a GCFC 11 combination glass electrode was used for pH measurements. Determination of mercury was performed with a flame atomic absorption spectrometer GBC model 902AA (GBC Scientic® Equipment, Dundenong, Vic., Australia) using an air—acetylene flame in the optimization steps and an atomic absorption spectrometer model GBC 902AA with continuous flow hydride generator HG3000 in quantitative and real sample analysis. GBC HG 3000 continuous-flow vapor system equipped with a gas—liquid separator was used for HgH generation. A mercury hollow cathode lamp was used as a light source at 354 nm and 0.5 nm band width. FT-IR spectra were recorded in the range of 400—4000 cm-1 using Bruker Tensor 27 FTIR spectrometer (Germany) in KBr pellets. The thermal analysis studies were carried out using TG/DTA-SII (Perkin Elmer-USA). A syringe was available from BD, USA (5 cm x 0.9 cm i.d). All glassware containers were carefully treated with 2.0 M nitric acid (guaranteed reagent) and rinsed with double distilled water.

Synthesis of EGDMA-VP-Hg2+ IIP. The IIP particles for the IIP-SPE method were prepared by dispersion polymerization technique. For this purpose, 2 mmoles of HgCl were dissolved in 15 mL of methanol then 4 mmoles VP, 20 mmoles EGDMA and 50 mg AIBN were added into the solution. The solution has been purged by nitrogen gas for 10 min, frozen

with liquid nitrogen to prevent any unwanted reaction and sealed under vacuum. The reaction of polymerization was performed in a water bath at 60°C for 24 h. After completing polymerization, the solid polymer was crushed, ground and sieved to obtain particles with diameters in the range of 55-75 ^m. Fine particles were removed by suspending polymer beads in acetone and decantation of acetone for three times. To remove templates, the remaining particles were treated with 1 M EDTA for 72 h, and the excess amount of EDTA was washed by water. The complete removal of template was followed by CV-AAS. Finally, the particles were dried under vacuum in a desiccator and used as a sorbent of SPE [32, 33]. Scheme schematically represents the synthesis of ion-imprinted polymer:

N

+

HgCl2

EGDMA AIBN

^=N N-

Preparation of IIP-SPE column. IIP-SPE columns were prepared by packing the dry IIP particles (500 mg) in a 5 mL empty syringe. The syringe was attached with a stop cock and two sieve plates at the bottom end and the top end of IIP packed particles. The sieve plates were obtained from commercial SPE cartridges. The IIP-SPE columns were washed out with 10 mL 0.1 M EDTA to remove impurities. Before loading sample solutions, the polymer should be activated through 5 mL water rinse.

General method for SPE of Hg2+. Extraction step: 5 mL of the model solution containing 50 mg/L Hg2+ were prepared in double distillated water. The resulting solution was loaded on to the IIP-SPE column in 1 mL/min flow rate. Elution step: the retained Hg2+ ions were stripped with 5 mL 0.1 M EDTA and subsequently the concentrated Hg2+ were determined by AAS. Regeneration step: in order to use the IIP-SPE column for the next measurement, the IIP-SPE column was washed with 5 mL 0.1 M EDTA and 5 mL water. In this process, the absorbed Hg2+ and another impurity were removed completely from IIP-SPE column.

Selectivity studies. The selectivity of Hg2+ IIP particles was studied for Hg2+, Na+, Cu2+, Pb2+, Cd2+, Ca2+ and Mg2+. The aqueous sample solutions containing 5 mL of Hg2+/Na+, Hg2+/Cu2+, Hg2+/Pb2+, Hg2+/Cd2+, Hg2+/Ca2+ and Hg2+/Mg2+ were passed through imprinted or non-imprinted polymer column at a flow rate of 1 mL/min by vacuum system. After the extraction, the extracted metal was eluted from the column using 0.1 M EDTA aqueous solution and then the determination of retained mercury(II) was done by

Transmittance, % 1.0

0.8

0.6

0.4

0.2

O-H

C-H

C=O

500 1000 1500 2000 2500 3000 3500 4000

Wavenumber, cm-1

Fig. 1. IR spectra of mercury imprinted polymer.

AAS. The effect of imprinting on selectivity was defined as:

K = ((с, - cf)/cf)(V/m),

(1)

where Kd is the distribution coefficient, ci and cf the initial and final solution concentrations, respectively, V the volume of the solution used for extracting and m is the weight of polymer used for extra

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