научная статья по теме SIMULTANEOUS EXTRACTION OF TRACE AMOUNTS OF COBALT, NICKEL AND COPPER IONS USING MAGNETIC IRON OXIDE NANOPARTICLES WITHOUT CHELATING AGENT Химия

Текст научной статьи на тему «SIMULTANEOUS EXTRACTION OF TRACE AMOUNTS OF COBALT, NICKEL AND COPPER IONS USING MAGNETIC IRON OXIDE NANOPARTICLES WITHOUT CHELATING AGENT»

ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2013, том 68, № 11, с. 1067-1072

ОРИГИНАЛЬНЫЕ СТАТЬИ

УДК 543

SIMULTANEOUS EXTRACTION OF TRACE AMOUNTS OF COBALT, NICKEL AND COPPER IONS USING MAGNETIC IRON OXIDE NANOPARTICLES

WITHOUT CHELATING AGENT © 2013 Sayed Zia Mohammadi1,2, Hooshang Hamidian1,2, Laleh Karimzadeh1, Zahra Moeinadini1

department of Chemistry, Payame Noor University

P.O. Box 19395-4697, Tehran, Iran 2Department of Chemistry, Payame Noor University Kerman, Iran Received 14.03.2011; in final form 23.03.2012

The present study investigates the application of Fe3O4 nanoparticles as an adsorbent for solid phase extraction and subsequent determination of trace amounts of cobalt, nickel and copper in environmental water samples using flame atomic absorption spectroscopy. The analyte ions were adsorbed on Magnetic nanoparticles in the pH range of 10—12 and then, Fe3O4 nanoparticles were easily separated from the aqueous solution by applying an external magnetic field and decantation. Hence, no filtration or centrifugation was needed. After extraction and collection of magnetic nanoparticles, the analyte ions were desorbed using 1.0 M HNO3. Several factors that may affect the preconcentration and extraction process, including pH, type and volume of eluent, sample volume, salt effect and matrix effect were optimized. Under the optimized conditions, linearity was maintained from 0.005 to 3.0 p.g/mL for cobalt and nickel and from 0.001 to 1.25 p.g/mL for copper in the initial solution. The detection limits of this method for cobalt, nickel and copper ions were 0.9, 0.7 and 0.3 ng/mL, respectively. Finally, the method was successfully applied to the extraction and determination of the analyte ions in natural waters and reference plant samples.

Keywords: magnetic iron oxide nanoparticles, preconcentration, solid phase extraction, water analysis.

DOI: 10.7868/S0044450213110157

The quantification of trace metals in environmental samples ofwide ranging composition has routinely been done by flame atomic absorption spectrometry (FAAS) [1—4], electrothermal atomic absorption spectrometry [5], inductively coupled plasma mass spectrometry [6, 7] and inductively coupled plasma optical emission spectrometry [8, 9].

However, most of aforementioned methods except FAAS are expensive and an increased instrumentation complexity, limiting its widespread application to routine analytical works. FAAS is still being used because it combines a fast analysis time, relative simplicity and low cost. All of these features have been responsible for its broad utilization in the determination of trace elements in different samples [1—3]. However, trace level determination of metal ions by flame atomic absorption spectrometry is difficult due to the lower levels of metal ions than the limit of detection of FAAS and effects of the matrix components [1]. To overcome these limitations on the determination of metal ions by FAAS, separation-enrichment techniques such as solid phase extraction (SPE), cloud point extraction, liquid—liquid extraction, coprecipitation, etc. [1—4, 10— 17] have been used by other researchers.

SPE technique has become increasingly popular in comparison with the traditional liquid—liquid extraction methods because of the following advantages: (i) simple operation; (ii) high preconcentration factor; (iii) rapid phase separation; (iv) the possibility of combination with different detection techniques and (v) time-saving and cost-saving [8].

Nanometer-sized material is a new solid material that has gained importance in recent years due to its special properties [18, 19] as an ultrafine-grained particle. In recent years, nanometer-sized alumina [6, 20], magnetic iron oxide nanoparticles (MIONs) [21—26] and nanometer-sized titania [8] have been applied to the separation of trace organic compounds and metal ions in various samples.

A major advantage of using MIONs as sorbent is the possibility of collection of the particles by application of a magnetic field in a batch system. This makes magnetic nanoparticles excellent candidates for combining adsorption properties with ease of phase separation [27].

To the best of our knowledge, there has been no study on the use of MIONs for the separation and preconcen-

Fig. 1. SEM image of MIONPs.

tration of trace metals without addition of chelating agent and without any modification of MIONs. Therefore, the main objective of this study is to investigate the preconcentration of Co(II), Ni(II) and Cu(II) on MIONs, prior to FAAS determination in water and certified environmental samples.

EXPERIMENTAL

Reagents and solutions. All chemicals were of analytical-reagent grade and all solutions were prepared with de-ionized water. The laboratory glassware were kept overnight in a 1.4 M HNO3 solution. Before using, all of the glassware were washed with de-ionized water and dried. The stock standard solutions (1.0 mg/mL) of Co, Ni and Cu were obtained from the Merck (Darmstadt, Germany). The working reference solutions were obtained daily by stepwise dilution from stock solution with de-ionized water. A solution of10%(w/v) NaCl (Merck) was prepared by dissolving of 10 g of NaCl in 100 mL of de-ionized water. The solution of alkali metal salts (1% w/v) and various metal salts (0.1% w/v) were used to study the interference ions.

Instrumentation. A SensAA GBC atomic absorption spectrometer (Dandenong, Australia) equipped with deuterium background correction and air-acetylene burner was used for absorbance measurements according to instrument manufacturer instruction. Cobalt, nickel and copper hollow cathode lamps were used as light source. The operating parameters of elements were set according to the manufacturer recommendation. The acetylene flow rate and the burner height were adjusted in order to obtain the maximum absorbance signal, while aspirating the analyte solution. A Metrohm 692 pH (Herisau, Switzerland) was used for pH measurements.

Preparation of MIONs. The MIONs were synthesized according to the method described in literature [28] by coprecipitation of a stoichiometric mixture of ferrous and ferric chlorides (molar ratio 1 : 2) in an ammonium hydroxide solution with constant stirring. The nanoparticles were collected by the magnet and thoroughly washed with de-ionized water to remove excess amounts of ammonium hydroxide.

Characterization of MIONPs. The microstructure of the MIONs was observed by scanning electron microscope (SEM) (Cam Scan MV2300) and is shown in Fig. 1. Scanning electron micrograph was recorded without sample coating. This figure shows that the adsorbent had a regular surface, indicating relatively high surface area.

General procedure. The extraction procedure was carried out in a batch process mode. All standards and samples were prepared for analysis according to the following procedure. 50.0 mL of each standard and sample were placed in a beaker. To each beaker, 2 mL of 0.1 M phosphate buffer (pH 11), 1 mL of10% (w/v) NaCl and 10 mg MIONs were added. Then, beakers were stirred for 2 min. The beaker was placed on the magnet and nanoparticles were collected. After decanting the supernatant solution, the collected MI-ONs were washed with 1.5 mL of 1.0 M HNO3 solution in order to desorb the adsorbed ions. Then, ana-lyte ions in the eluent were determined by FAAS.

Sample preparation. Tow certified reference materials (CRMs) furnished by the National Institute of Environment Studies (NIES) No. 1 Pepperbush and NIES No. 7 Tea Leave were analyzed. Approximately 1.0 g of NIES No. 1 and NIES No. 7 were weighted accurately in a Teflon cup and dissolved in concentrated nitric acid (~10 mL) with heating on a water bath. The solution was cooled, diluted and filtered. The volume of filtrate was increased to 100 mL with adding de-ionized water to it in a calibrated flask. An aliquot of the sample solution was taken individually, and analyte ions were determined through the general procedure.

River and well water samples were collected in acid-leached polyethylene bottles. The river water samples were collected from Shahdad, Rayen and Ko-hpayeh in Kerman, Iran. The well water sample was taken from Payame Noor University, Kerman, Iran.

SIMULTANEOUS EXTRACTION OF TRACE AMOUNTS OF COBALT,

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The only pretreatment was the acidification of samples to pH 2 with nitric acid, which was performed immediately after collection, in order to prevent the adsorption of metal ions on the flask walls. The samples were filtered before analyses through a cellulose membrane (Millipore, Bedford, MA, USA) with 0.45 ^m pore size.

RESULTS AND DISCUSSION

In this study, a combination of SPE and FAAS was developed for the determination of trace amounts of cobalt, nickel and copper. Several factors that may affect the preconcentration and extraction process, including pH, type and volume of eluent, sample volume and matrix effect were optimized. The optimizations were carried out on 50 mL of aqueous solution containing 0.1 ^g/mL of cobalt, nickel and copper ions.

Effect of pH. Since the pH of the aqueous sample solutions is an important analytical factor in the solid phase extraction studies of metal ions, the influence of pH on the preconcentration of the analyte ions was examined in the pH range of 3—12, keeping the other parameters constant. pH of the metal sample solutions was adjusted by using NaOH and HNO3 solutions. The results are given in Fig. 2. The results showed that maximum recovery of the analyte ions were obtained in the pH range of 10—12. Accordingly, the further studies were done at pH 10.5 by using 0.1 M phosphate buffer solutions. Additional experiments on volume of buffer showed that 2 mL of buffer solution would give the best results. Therefore, 2 mL of 0.1 M phosphate buffer solution was used in all subsequent experiments.

Effect of the adsorbent amount. The required amount of MIONs for the complete adsorption of the analyte ions in 50 mL solution containing 1.0 ^g o

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