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Simultaneous preconcentration of bismuth and lead ions on modified magnetic core–shell nanoparticles and their determination by ETAAS
Chemical Engineering Journal 281 (2015) 444–452
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Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej
Simultaneous preconcentration of bismuth and lead ions on modified magnetic core–shell nanoparticles and their determination by ETAAS Matin Naghizadeh a,b, Mohammad Ali Taher a, Mansoureh Behzadi a,b,⇑, Firouzeh Hassani Moghaddam a,b a b
Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iran Young Researchers Society, Shahid Bahonar University of Kerman, Kerman, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A new nanoadsorbent based on
modified magnetic core–shell Fe3O4@SiO2 was successfully prepared. It was used to extract bismuth and lead ions from various samples simultaneously. It is a very fast extraction method and exhibits very good adsorption capacity and analytical performance.
a r t i c l e
i n f o
Article history: Received 18 May 2015 Received in revised form 1 July 2015 Accepted 3 July 2015 Available online 9 July 2015 Keywords: Magnetic solid-phase extraction Core–shell silica nanoparticles Electrothermal atomic absorption spectrometry Bismuth Lead
a b s t r a c t Magnetic core–shell silica nanoparticles modified by 3-[2-(2-aminoethylamino)ethylamino]propyl-trime thoxysilane (AAAPTS) were prepared and used as new adsorbent for simultaneous extraction and preconcentration of bismuth and lead ions through magnetic solid-phase extraction (MSPE) method. After adsorption, these ions were desorbed with nitric acid followed by determination with electrothermal atomic absorption spectrometry. Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) spectrometry and vibrating sample magnetometer (VSM) were used to characterize the adsorbent. The MSPE conditions were optimized. The detection limits of 1.4 and 3.7 ng L 1 were obtained for bismuth and lead, respectively. The linear range was 0.003–0.200 ng mL 1 for bismuth and 0.02–0.700 ng mL 1 for lead. The relative standard deviations of the method for eight replicate determination of 0.07 and 0.35 ng mL 1 of Bi(III) and Pb(II) were ±3.6% and ±3.1%, respectively. The method was applied for the determination of target ions in different samples with high recoveries. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction Nowadays, simultaneous extraction and preconcentration of several metal ions at trace levels from various real matrices has
⇑ Corresponding author at: Department of Chemistry, Shahid Bahonar University of Kerman, 22 Bahman Boulevard, P.O. Box 76169-133, Kerman, Iran. Tel./fax: +98 341 3222033. E-mail address: [email protected] (M. Behzadi). http://dx.doi.org/10.1016/j.cej.2015.07.014 1385-8947/Ó 2015 Elsevier B.V. All rights reserved.
great importance [1]. In this work, a sensitive procedure for extraction and preconcentration of Bi(III) and lead(II) has been described simultaneously. Bismuth and its compounds have been used in many different areas such as cosmetic products, lubricating oils, medicines, pigments, electronics, semiconductors, alloys industry and in recycling of uranium nuclear fuels [2–4]. It is also found as a secondary component in some tin, copper and lead minerals [5]. Neuropathology, osteoarthropathy, nephropathy and hepatitis have been attributed to bismuth compounds as toxic effects in
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humans [6]. Lead is widely used in chemical and plastic industries, battery manufacturing, smelting, pigment products, printing industries and mining [7]. It is considered as dangerous toxic metal to the environment and human health [8]. The binding of Pb(II) to serum albumin is very strong and there are many binding site for the binding of Pb(II) on albumin protein. In addition, it affects the functional properties of albumin [9]. Accumulation of lead in the vital organs can cause poisoning, brain and kidney damage, anemia and cancer [10]. From this point of view, bismuth and lead have been distributed in environment increasingly. Therefore, the trace analysis of these metals is necessary. Several analytical methods, e.g. electrochemical methods [11], atomic absorption spectrometry [12–14], inductively coupled plasma-atomic emission spectroscopy [15] and etc. have been reported for the determination of Bi(III) and Pb(II). But, the direct determination of trace metal ions is often limited due to the low concentration and strong interference from the real sample matrices. To enrich the metal ion concentration and remove the target analytes from the sample matrices, a separation and preconcentration step such as coprecipitation [16], solvent extraction [17], cloud point extraction (CPE) [18], solid-phase extraction (SPE) [19,20] and magnetic solid-phase extraction (MSPE) [21,22] have been applied. Recently, MSPE has been intensively used for environmental analysis at trace levels [21–24]. In this technique, magnetic nanoparticles (MNPs), as adsorbent, are served without any packing of cartridges. They are just added into a sample solution containing target analytes. After adsorption, MNPs can be easily removed from sample solution using a magnet placed outside of the extraction container. Therefore, the main advantages of MSPE include low price, rapidity, simplicity and reusability [24]. However, naked MNPs tend to form agglomerates, as well as, they are chemically active and oxidize in air, resulting in loss of magnetism [25]. Thus, it is necessary to coat them with inorganic layer such as silica or alumina [26]. Silica protective shell not only stabilize the MNPs, but can also be used for surface modification with specific compounds, for instance, a wide range of organic ligands or other functional groups, depending on the desired application [27–29]. 3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilan e (AAAPTS) is a reagent which is used to modify the surface of inorganic materials and organic polymers [30,31]. It has more amino groups with free lone pair of electrons on nitrogen atoms. Therefore, these atoms are suitable sites for coordination with metal ions effectively. Here, we successfully prepared an adsorbent based on magnetic core–shell Fe3O4@SiO2 nanoparticles modified with AAAPTS. Then, this adsorbent was applied in MSPE for preconcentration of Bi(III) and Pb(II) simultaneously prior to electrothermal atomic absorption spectrometric (ETAAS) determination.
2. Experimental 2.1. Reagents and apparatus Stock solutions of bismuth and lead were prepared by dissolving of Bi(NO3)35H2O and Pb(NO3)2 (Merck, Darmstadt, Germany) into deionized water. Working solutions were prepared daily by appropriate dilution of stock solutions. FeCl36H2O, FeCl24H2O, NH3, ethanol and HNO3 were analytical grades and purchased from Merck Company. Tetraethyl orthosilicate (TEOS) for preparing silica shell on magnetic nanoparticles was also obtained from Merck. 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysi lane (Acros organics, New Jersey, USA) was used to prepare the modified adsorbent in this study. High purity reagents from Sigma (St. Louis, MO, USA) were used for studying interference effects.
Table 1 Instrumental parameters and thermal program of ETAAS for the determination of bismuth and lead ions. Parameter
Bi
Pb
Instrumental parameters Wavelength (nm) Spectral bandwidth (nm) Lamp current (mA) Signal measurement Sample volume (lL)
223.3 0.1 10 Peak Height 20
283.1 0.5 5 Peak Height 20
Step
Furnace temp. (°C) Bi
Pb
Drying Drying Drying Ashing Ashing Atomization Atomization Cleaning up
85 95 120 400 400 2000 2000 200
85 95 120 400 400 2100 2100 2300
Time(s)
Argon flow rate (L min
5.0 40 10 6.0 2.0 1 2.0 2.0
3.0 3.0 3.0 3.0 0.0 0.0 0.0 3.0
1
)
The concentrations of Bi(III) and Pb(II) were measured by a model Spectra AA 220 apparatus (Varian, Victoria, Australia) atomic absorption spectrometer with an electrothermal atomizer and autosampler. Optimum operating parameters for them are given in Table1. The samples were weighed using an electronic balance Mettler AE-160 (Greifensee, Switzerland). The pH measurements were carried out with a Metirohm 827 pH-meter (Herisau, Switzerland) supplied with a combined glass–calomel electrode. Magnetic stirrer hot plate and mechanical stirrer (2000 rpm) and oven model 100 (Memmert, Frankfurt, Germany) were used to homogenize. To disperse the nanoparticles in solutions, a Sonorex digitec model DT 225H with 35 kHz ultrasonicator (Bandelin, Berlin, Germany) was used. Fourier transform infrared (FT-IR) spectra (4000–400 cm 1) in KBr were taken using a Tensor 27 spectrometer (Bruker, Saarbrucken, Germany) with spectral resolution better than 1 cm 1. Field emission-scanning electron microscopy (FE-SEM) images were obtained on a model Hitachi S-4160 (Tokyo, Japan) with an accelerating voltage of 20 kV. The samples were loaded onto a glass surface previously sputter coated with a homogeneous gold layer for charge dissipation during the SEM imaging. A LEO 912AB transmission electron microscope (TEM), (Carl Zeiss Inc., Jena, Germany) was used with an accelerating voltage of 100 kV. Samples were first dispersed in water and then collected using carbon-film-covered copper grids for analysis. The powder X-ray diffraction (XRD) patterns were examined on a model X’PertPro diffractometer (Panalytical, Almelo, The Netherlands) using Cu Ka radiation (wavelength = 1.54 Å). The data were collected over a range of 10–80° 2h with a step size of 0.01°, nominal time per step of 2 s and slit width 5 nm. Magnetic measurements were carried out using a vibrating sample magnetometer (VSM) model MDKFD (Danesh Pajohan Kavir Co. Kashan, Iran).
2.2. Preparation of Fe3O4 magnetic nanoparticles The preparation of Fe3O4 magnetic nanoparticles was based on dissolving FeCl36H2O (11.68 g) and FeCl24H2O (4.30 g) in 200 mL deionized water. Then, this solution was stirred with mechanical stirrer (1000 rpm) at 80 °C for 30 min. Nitrogen gas was continually bubbled through this solution to expel oxygen. Following that, 25 mL of 25% NH3 was rapidly added to the solution. After that, the color of bulk solution changed from orange to black immediately. The magnetite precipitates were collected by a magnet after
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Fig. 1. Effect of extraction parameters on the extraction efficiency: (A) pH, (B) type and concentration of eluent, (C) eluent volume, (D) nanoadsorbent amount, (E) ultrasonication time and (F) sample volume; The concentration of Bi(III) and Pb(II) were 0.05 ng mL 1 and 0.3 ng mL 1, N = 3.
washing several times with deionized water and then with ethanol. Finally, they were dried in oven at 80 °C for 18 h.
collected by a magnet, rinsed with deionized water, ethanol and dried in the oven at 80 °C for 8 h.
2.3. SiO2 coating of the Fe3O4 magnetic nanoparticles 2.4. Surface modification of core–shell Fe3O4@silica with AAAPTS To protect the magnetic core by the silica film and prepare core–shell magnetic nanoparticles, the as-prepared Fe3O4 (0.5 g) were dispersed in a solution composed of 80 mL ethanol and 20 mL double distilled water by sonicating for 30 min. Then, 5 mL ammonia solution (25 wt%) and 4 mL TEOS were added sequentially. The resulting suspension was stirred and allowed to react for 24 h at room temperature. Finally, the product was
The core–shell Fe3O4@silica nanoparticles (600 mg) were suspended in 80 ml of dry toluene under nitrogen atmosphere. After the addition of AAAPTS (4 mL), the mixture was refluxed at 80 °C for 24 h. The resulting product, as adsorbent, was collected with a magnet, washed with dry toluene, deionized water and ethanol and then dried at room temperature.
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Fig. 2. FT-IR spectra of (A) Fe3O4, (B) Fe3O4@SiO2, (C) AAAPTS and (D) Fe3O4@SiO2@AAAPTS nanoparticles.
Fig. 3. FE-SEM (A1 & A2) and TEM (B1 & B2) images of the nanoadsorbent particles.
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Fig. 4. XRD patterns of (A) Fe3O4, (B) Fe3O4@SiO2 and (C) Fe3O4@SiO2@AAAPTS nanoparticles.
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structures that plays an important role in the enhancement of the adsorption capacity. The TEM images showed that these nanoparticles had entrapped in the silica shell successfully. Also, the diameter of the magnetic core is lower than 50 nm.
Fig. 5. VSM curves of (A) Fe3O4, (B) Fe3O4@SiO2 and (C) Fe3O4@SiO2@AAAPTS nanoparticles.
2.5. Magnetic solid-phase extraction procedure MSPE was carried out as follows. A portion of 25 mL sample solutions containing 0.05 ng mL 1 Bi(III) and 0.3 ng mL 1 Pb(II) were transferred into a 100 mL glass flask and the pH was adjusted to 6.5 using HCl solution. Then, 250 mg of the synthesized Fe3O4@SiO2@AAAPTS was added and the mixture was ultrasonicated for 5 min. In this step, the analytes were adsorbed on the adsorbent. Then, a piece of magnet was placed outside the flask to collect adsorbent and the supernatant was decanted directly. In desorption step, 3.0 mL HNO3 (3.0 mol L 1) was added as eluent and ultrasonicated for 5 min. Finally, the magnet was used again to collect the nanoparticles, and the eluent was transferred into a test tube for subsequent ETAAS analysis. 3. Results and discussion 3.1. Characterization of Fe3O4@SiO2@AAAPTS nanoparticles 3.1.1. FT-IR spectroscopy The FT-IR spectrum of Fe3O4 nanoparticles shows the absorption peak at 562 cm 1 which corresponding to the Fe–O vibration (Fig. 2A). The silica shell coated on the surface of magnetite core can be confirmed by the spectrum in Fig. 2B. The bands at 1092 cm 1 and 799 cm 1 are assigned to Si–O–Si vibrations, the peak at 948 cm 1 was related to the vibration of Si–OH group and the absorption peak of Fe3O4 at 573 cm 1 indicated that MNPs is covered by silica layer through experiment. In the spectrum of AAAPTS (Fig. 2C), the peaks at 3292 cm 1 and 1593 cm 1 can be assigned to N–H stretching and bending vibrations, respectively. The two peaks at 2937 cm 1 and 2839 cm 1 are due to asymmetrical and symmetrical C–H stretching vibrations and C–H bending peak is observed at 1462 cm 1. The band at 1194 cm 1 is ascribed to the stretching of the C–N stretching bonds. Another two peaks at 1082 cm 1 and 819 cm 1 might be ascribed to Si–O–Si vibrations. Also, the surface modification of core–shell nanoparticles can be confirmed by FT-IR (Fig. 2D). The two peaks at 468 cm 1 and 576 cm 1 are due to Fe–O–Si and Fe–O stretching vibrations, respectively. 3.1.2. FE-SEM and TEM images The morphological feature of the synthesized Fe3O4@SiO2@ AAAPTS nanoparticles were characterized by FE-SEM and TEM images and shown in different magnification (Fig. 3). The FE-SEM images showed the MNPs have relatively homogeneous and porous
3.1.3. XRD patterns The typical XRD patterns of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@AAAPTS nanoparticles are shown in Fig. 4. The diffraction peaks (2h = 30.2°, 35.5°, 43.1°, 53.4°, 57.1° and 62.8°) related to (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0), can be indexed to face-centered cubic structure of magnetite. Also, board peak at low diffraction angle (2h = 16–28°) which corresponded to the amorphous peak of SiO2 was displayed in Fig. 4B. AAAPTS modified Fe3O4@SiO2 surface can be confirmed from the XRD data (Fig. 4C). The characteristics diffraction peaks that correspond to Fe3O4 and SiO2 can be observed. There also exist other diffraction peaks which can be attributed to the reflection of methoxysilane group in AAAPTS that were overlapped with other peaks. 3.1.4. Magnetic measurements Fig. 5 shows that the saturation magnetization values were 72.3, 44.1, and 38.7 emu g 1 for Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@AAAPTS, respectively. Compared with the Fe3O4, the saturation magnetization of Fe3O4@SiO2@AAAPTS reduced to 38.7 emu g 1, but it is sufficient for magnetic separation with a conventional magnet. 3.2. Optimization of extraction conditions Several experimental variables affecting the extraction recovery of bismuth and lead ions were investigated, including, sample pH, the eluting solvent, the adsorbent amount, ultrasonic time and sample volume. In all optimization experiments one-at-a-time strategy was used. 3.2.1. Effect of pH The sorption ability of bismuth and lead ions by the as-prepared modified MNPs is significantly dependent on the pH value of the aqueous solution. The influence of pH on the extraction recovery of target ions was tested in the range 3–8, when the other parameters were kept constant. Fig. 1A shows the recovery percentage increased along with increasing pH value from 3 to 6.5 and maximum recovery was obtained at pH 6.5. When the pH was further enhanced from 6.5 to 8, the recovery percentage decreased silently. Because, the precipitation reactions may occur for Pb(II) and Bi(III) ions. Therefore, pH 6.5 was selected in the following experiments. 3.2.2. Effect of eluent The effect of type and volume of eluent on the recovery of Bi(III) and Pb(II) was investigated. As can be seen from Fig. 1A, the sorption of these ions on the adsorbent at acidic solution is low. It means that desorption can be done in this media. Therefore, various acidic solutions were used as eluent and the results showed that HNO3 with the concentration of 3 mol L 1 was the best ones (Fig. 1B). Also, the eluent should elute analytes quantitatively in a small volume. Thus, the volume range of 0.5–5 mL was tested and the results were shown in Fig. 1C. Finally, 3 mL of 3 mol L 1 HNO3 was chosen for the elution. 3.2.3. Effect of Fe3O4@SiO2@AAAPTS amount In the MSPE technique, the amount of magnetic adsorbent is one of the main factors effecting on the extraction of the analytes. Hence, this parameter was studied in the range 0.005–0.1 g. the results indicate the recovery percentage increased with an increase in the adsorbent content which could be due to the availability of more sorption sites and larger surface area. After a certain value
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Table 2 Effect of coexisting ions. Foreign ion +
Na Cl K+ NO3 NH+4 CH3COO Ca2+ Zn2+ Cd2+ Al3+ Co2+ Mo6+ Cr3+ Fe3+ Fe2+ EDTA
Table 4 Determination of bismuth and lead ions in real samples.
Foreign ion/Pb ratio
Foreign ion/Bi ratio
Recovery (%)a
2000 2000 2000 2000 2000 2000 1000 1000 1000 1000 1000 1000 1000 1000 1000 500
2000 2000 2000 1000 700 1000 1000 650 1000 1000 550 1000 850 1000 1000 400
100.8 ± 1.2 100.5 ± 3.4 98.2 ± 3.9 97.8 ± 2.3 98.8 ± 3.6 96.6 ± 5.2 99.1 ± 3.6 98.9 ± 2.8 97.4 ± 3.7 99.6 ± 3.3 96.0 ± 2.6 97.7 ± 4.5 102.1 ± 3.6 96.8 ± 4.9 98.9 ± 4.5 95.4 ± 3.2
Samples
Tap waterb
Well waterc
Human hair (pg g -1)
a
Under optimum conditions. a Mean ± standard deviation (N = 3).
b c
(0.025 g), no further increase in percent occurred as an increase in adsorbent content (Fig. 1D). So, 0.025 g was used in the all subsequent experiments.
3.2.4. Effect of ultrasonication time In this method, for both adsorption and desorption, ultrasonic treatment times in the range 1–20 min were investigated. The experimental results indicated that 5 min was sufficient for achieving quantitative recovery of bismuth and lead ions for both adsorption and desorption (Fig. 1E).
3.2.5. Effect of sample volume The sample volume is an important parameter to obtain a high enrichment factor. Experimental analysis showed (Fig. 1F) that, when sample volume was 600 mL, quantitative recovery was obtained and theoretical enrichment factors were 200 for both target ions. But in experimental state, enrichment factors were 152 and 163 for Bi(III) and Pb(II), respectively.
Spiked (ng L 1)
Founda (ng L
1
Recovery (%)
Bi
Pb
Bi
Pb
Bi
Pb
0.0 20.0 40.0 80.0 0.0 20.0 40.0 80.0 0.0
0.0 30.0 60.0 90.0 0.0 30.0 60.0 90.0 0.0
8.1 ± 0.05 28.2 ± 0.11 48.6 ± 0.15 87.7 ± 0.19 8.9 ± 0.04 29.1 ± 0.12 47.5 ± 0.13 88.5 ± 0.22 9.4 ± 0.06
21.0 ± 0.09 52.0 ± 0.16 80.0 ± 0.18 113.0 ± 0.25 23.0 ± 0.14 52.0 ± 0.15 82.0 ± 0.21 114.0 ± 0.26 430.0 ± 0.30
– 100.5 101.3 99.50 – 101.0 96.50 99.50 –
– 103.3 98.30 102.2 – 96.60 98.30 101.1 –
20.0 40.0 80.0
30.0 40.0 60.0
29.1 ± 0.11 49.0 ± 0.14 89.7 ± 0.17
459.2 ± 0.32 469.5 ± 0.31 490.2 ± 0.33
98.50 99.00 100.4
97.30 98.80 100.3
)
Mean ± SD (N = 3). Kerman drinking water, Kerman, Iran. Shahid Bahonar University of Kerman, Kerman, Iran.
3.3. Adsorption capacity The adsorption capacity is an important factor to evaluate the Fe3O4@SiO2@AAAPTS nanoadsorbent. It is the maximum analytes quantity taken up by 1.0 g of synthesized nanoadsorbent. In order to determine this factor, 50 mg of the nanoadsorbent were subjected to several loadings with 25 mL sample solutions containing Bi(III) and Pb(II) with pH = 6.5 and then, followed by the determination of retained analytes using ETAAS. The values of adsorption capacity increased with the increase of initial concentrations of target ions and then it reached a plateau. The static adsorption capacity (13.61 mg g 1 for lead ions and 12.22 mg g 1 for bismuth ions) of the nanoadsorbent was obtained. 3.4. Effect of coexisting ions interference Under optimized conditions, the interference of various cations and anions on the recovery of bismuth and lead ions was investigated. Results obtained showed that Fe3O4@SiO2@AAAPTS is a good
Table 3 Comparison of linear range (LR), limits of detection (LOD) and relative standard deviation (RSD) of this method with other reported methods for preconcentration of bismuth and lead ions. Analytical technique a
FI -SPE-ETAAS FI-CPEb-ICPc-AESd USAEMEe-ICP-OESf SFODMEg-ETVh-ICP-MSi j
SPE-FAAS
MSPE-ETAAS a b c d e f g h i j
1)
Metal ions
LR (lg L
Bi Pb Bi Pb Bi Pb Bi Pb Bi Pb Bi Pb
– – 1–50 – 1–1000 1–1000 0.02–20 0.05–20 – 5–20000 0.003–0.2 0.02–0.7
Flow injection. Cloud point extraction. Inductively coupled plasma. Atomic emission spectroscopy. Ultrasonic-assisted emulsification microextraction. Optical emission spectrometry. Solidified floating organic drop microextraction. Electrothermal vaporization. Mass spectrometry. Flame atomic absorption spectroscopy.
LOD (lg L 0.013 0.0045 0.12 – 0.48 5.6 0.0041 0.017 – 1.0 0.0014 0.0037
1
)
RSD (%)
Refs.
5.3 3.8 2.3 – 1.8 5.6 4.6 4.6 – 3.8 3.6 3.1
[32] [33] [34] [35] [36] This work
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candidate to preconcentration of target analytes without any serious matrix interference in different real samples (Table 2). 3.5. Analytical performance Under optimized conditions, linear range (LR), limits of detection (LODs) and repeatability were studied. The obtained linearity was 0.003–0.200 ng mL 1 for Bi(III) and 0.02–0.700 ng mL 1 for Pb(II). The LODs (defined as 3Sdblank/m, where Sd is the standard deviation of the blank readings for ten replicate analysis and m is the slope of the calibration curve) was 1.4 ng L 1 and 3.7 ng L 1 for bismuth and lead, respectively. Also, the resultant repeatability expressed as relative standard deviations (RSD, N = 8) were calculated as 3.6% and 3.1% for 0.07 ng mL 1 and 0.35 ng mL 1 concentration of Bi(III) and Pb(II), respectively. In Table 3, a comparison of the developed method with the other reported preconcentration methods [32–36] for determination of target analytes was done. As this table shows, the LODs found in the present work are better than other works reported elsewhere. Also, the RSD% and linearity values are comparable with the values reported for other methods. 3.6. Analysis of the real samples The method was applied to the determination of trace amounts of Bi(III) and Pb(II) in a variety of samples. The samples were also analyzed after spiking with different concentrations of bismuth and lead ions with high recoveries. Tap water, well water, and human hair samples were analyzed. The analytical results are presented in Table 4. The results show that the method is suitable for the analysis of real samples. 4. Conclusion Fe3O4@SiO2@AAAPTS nanoparticles with good saturation magnetization have been successfully prepared and used as a novel and effective adsorbent for simultaneous extraction and preconcentration of bismuth and lead ions from aqueous solutions prior to determination by ETAAS. It is a very fast extraction method, because the MNPs have generally high surface area and fast magnetic separation. Ease of operation, high selectivity and sensitivity are other advantages. Also, the combination of MSPE by the as-prepared nanoadsorbent with ETAAS offers significant analytical performance. References [1] A.M. El-Toni, M.A. Habila, M.A. Ibrahim, J.P. Labis, Z.A. ALOthman, Simple and facile synthesis of amino functionalized hollowcore–mesoporous shell silica spheres using anionic surfactant for Pb(II), Cd(II), and Zn(II) adsorption and recovery, Chem. Eng. J. 251 (2014) 441–451. [2] A.K. Das, R. Chakraborty, M.L. Cervera, M. Guardia, Analytical techniques for the determination of bismuth in solid environmental samples, Trends Anal. Chem. 25 (2006) 599–608. [3] N. Yang, H. Sun, Biocoordination chemistry of bismuth: Recent advances, Coord. Chem. Rev. 25 (2007) 2354–2366. [4] A. Nosal-Wiercinska, The kinetics and mechanism of the electroreduction of Bi(III) ions from chlorates (VII) with varied water activity, Electrochim. Acta 55 (2010) 5917–5921. [5] J.A. Reyes-Aguilera, M.P. Gonzalez, R. Navarro, T.I. Saucedo, M. Avila-Rodriguez, Supported liquid membranes (SLM) for recovery of bismuth from aqueous solutions, J. Membr. Sci. 310 (2008) 13–19. [6] S. Itoh, S. Kaneco, K. Ohta, T. Mizuno, Determination of bismuth in environmental samples with Mg–W cell–electrothermal atomic absorption spectrometry, Anal. Chim. Acta 379 (1999) 169–177. [7] S. Hernberg, Lead poisoning in a historical perspective, Am. J. Ind. Med. 38 (2000) 244–254. [8] H. Needleman, Lead poisoning, Annu. Rev. Med. 55 (2004) 209–222. [9] E. Ayranci, O. Duman, Binding of lead ion to bovine serum albumin studied by ion-selective electrode, Protein Pept. Lett. 11 (2004) 331–337.
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Contents lists available at ScienceDirect
Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej
Simultaneous preconcentration of bismuth and lead ions on modified magnetic core–shell nanoparticles and their determination by ETAAS Matin Naghizadeh a,b, Mohammad Ali Taher a, Mansoureh Behzadi a,b,⇑, Firouzeh Hassani Moghaddam a,b a b
Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iran Young Researchers Society, Shahid Bahonar University of Kerman, Kerman, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A new nanoadsorbent based on
modified magnetic core–shell Fe3O4@SiO2 was successfully prepared. It was used to extract bismuth and lead ions from various samples simultaneously. It is a very fast extraction method and exhibits very good adsorption capacity and analytical performance.
a r t i c l e
i n f o
Article history: Received 18 May 2015 Received in revised form 1 July 2015 Accepted 3 July 2015 Available online 9 July 2015 Keywords: Magnetic solid-phase extraction Core–shell silica nanoparticles Electrothermal atomic absorption spectrometry Bismuth Lead
a b s t r a c t Magnetic core–shell silica nanoparticles modified by 3-[2-(2-aminoethylamino)ethylamino]propyl-trime thoxysilane (AAAPTS) were prepared and used as new adsorbent for simultaneous extraction and preconcentration of bismuth and lead ions through magnetic solid-phase extraction (MSPE) method. After adsorption, these ions were desorbed with nitric acid followed by determination with electrothermal atomic absorption spectrometry. Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) spectrometry and vibrating sample magnetometer (VSM) were used to characterize the adsorbent. The MSPE conditions were optimized. The detection limits of 1.4 and 3.7 ng L 1 were obtained for bismuth and lead, respectively. The linear range was 0.003–0.200 ng mL 1 for bismuth and 0.02–0.700 ng mL 1 for lead. The relative standard deviations of the method for eight replicate determination of 0.07 and 0.35 ng mL 1 of Bi(III) and Pb(II) were ±3.6% and ±3.1%, respectively. The method was applied for the determination of target ions in different samples with high recoveries. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction Nowadays, simultaneous extraction and preconcentration of several metal ions at trace levels from various real matrices has
⇑ Corresponding author at: Department of Chemistry, Shahid Bahonar University of Kerman, 22 Bahman Boulevard, P.O. Box 76169-133, Kerman, Iran. Tel./fax: +98 341 3222033. E-mail address: [email protected] (M. Behzadi). http://dx.doi.org/10.1016/j.cej.2015.07.014 1385-8947/Ó 2015 Elsevier B.V. All rights reserved.
great importance [1]. In this work, a sensitive procedure for extraction and preconcentration of Bi(III) and lead(II) has been described simultaneously. Bismuth and its compounds have been used in many different areas such as cosmetic products, lubricating oils, medicines, pigments, electronics, semiconductors, alloys industry and in recycling of uranium nuclear fuels [2–4]. It is also found as a secondary component in some tin, copper and lead minerals [5]. Neuropathology, osteoarthropathy, nephropathy and hepatitis have been attributed to bismuth compounds as toxic effects in
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humans [6]. Lead is widely used in chemical and plastic industries, battery manufacturing, smelting, pigment products, printing industries and mining [7]. It is considered as dangerous toxic metal to the environment and human health [8]. The binding of Pb(II) to serum albumin is very strong and there are many binding site for the binding of Pb(II) on albumin protein. In addition, it affects the functional properties of albumin [9]. Accumulation of lead in the vital organs can cause poisoning, brain and kidney damage, anemia and cancer [10]. From this point of view, bismuth and lead have been distributed in environment increasingly. Therefore, the trace analysis of these metals is necessary. Several analytical methods, e.g. electrochemical methods [11], atomic absorption spectrometry [12–14], inductively coupled plasma-atomic emission spectroscopy [15] and etc. have been reported for the determination of Bi(III) and Pb(II). But, the direct determination of trace metal ions is often limited due to the low concentration and strong interference from the real sample matrices. To enrich the metal ion concentration and remove the target analytes from the sample matrices, a separation and preconcentration step such as coprecipitation [16], solvent extraction [17], cloud point extraction (CPE) [18], solid-phase extraction (SPE) [19,20] and magnetic solid-phase extraction (MSPE) [21,22] have been applied. Recently, MSPE has been intensively used for environmental analysis at trace levels [21–24]. In this technique, magnetic nanoparticles (MNPs), as adsorbent, are served without any packing of cartridges. They are just added into a sample solution containing target analytes. After adsorption, MNPs can be easily removed from sample solution using a magnet placed outside of the extraction container. Therefore, the main advantages of MSPE include low price, rapidity, simplicity and reusability [24]. However, naked MNPs tend to form agglomerates, as well as, they are chemically active and oxidize in air, resulting in loss of magnetism [25]. Thus, it is necessary to coat them with inorganic layer such as silica or alumina [26]. Silica protective shell not only stabilize the MNPs, but can also be used for surface modification with specific compounds, for instance, a wide range of organic ligands or other functional groups, depending on the desired application [27–29]. 3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilan e (AAAPTS) is a reagent which is used to modify the surface of inorganic materials and organic polymers [30,31]. It has more amino groups with free lone pair of electrons on nitrogen atoms. Therefore, these atoms are suitable sites for coordination with metal ions effectively. Here, we successfully prepared an adsorbent based on magnetic core–shell Fe3O4@SiO2 nanoparticles modified with AAAPTS. Then, this adsorbent was applied in MSPE for preconcentration of Bi(III) and Pb(II) simultaneously prior to electrothermal atomic absorption spectrometric (ETAAS) determination.
2. Experimental 2.1. Reagents and apparatus Stock solutions of bismuth and lead were prepared by dissolving of Bi(NO3)35H2O and Pb(NO3)2 (Merck, Darmstadt, Germany) into deionized water. Working solutions were prepared daily by appropriate dilution of stock solutions. FeCl36H2O, FeCl24H2O, NH3, ethanol and HNO3 were analytical grades and purchased from Merck Company. Tetraethyl orthosilicate (TEOS) for preparing silica shell on magnetic nanoparticles was also obtained from Merck. 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysi lane (Acros organics, New Jersey, USA) was used to prepare the modified adsorbent in this study. High purity reagents from Sigma (St. Louis, MO, USA) were used for studying interference effects.
Table 1 Instrumental parameters and thermal program of ETAAS for the determination of bismuth and lead ions. Parameter
Bi
Pb
Instrumental parameters Wavelength (nm) Spectral bandwidth (nm) Lamp current (mA) Signal measurement Sample volume (lL)
223.3 0.1 10 Peak Height 20
283.1 0.5 5 Peak Height 20
Step
Furnace temp. (°C) Bi
Pb
Drying Drying Drying Ashing Ashing Atomization Atomization Cleaning up
85 95 120 400 400 2000 2000 200
85 95 120 400 400 2100 2100 2300
Time(s)
Argon flow rate (L min
5.0 40 10 6.0 2.0 1 2.0 2.0
3.0 3.0 3.0 3.0 0.0 0.0 0.0 3.0
1
)
The concentrations of Bi(III) and Pb(II) were measured by a model Spectra AA 220 apparatus (Varian, Victoria, Australia) atomic absorption spectrometer with an electrothermal atomizer and autosampler. Optimum operating parameters for them are given in Table1. The samples were weighed using an electronic balance Mettler AE-160 (Greifensee, Switzerland). The pH measurements were carried out with a Metirohm 827 pH-meter (Herisau, Switzerland) supplied with a combined glass–calomel electrode. Magnetic stirrer hot plate and mechanical stirrer (2000 rpm) and oven model 100 (Memmert, Frankfurt, Germany) were used to homogenize. To disperse the nanoparticles in solutions, a Sonorex digitec model DT 225H with 35 kHz ultrasonicator (Bandelin, Berlin, Germany) was used. Fourier transform infrared (FT-IR) spectra (4000–400 cm 1) in KBr were taken using a Tensor 27 spectrometer (Bruker, Saarbrucken, Germany) with spectral resolution better than 1 cm 1. Field emission-scanning electron microscopy (FE-SEM) images were obtained on a model Hitachi S-4160 (Tokyo, Japan) with an accelerating voltage of 20 kV. The samples were loaded onto a glass surface previously sputter coated with a homogeneous gold layer for charge dissipation during the SEM imaging. A LEO 912AB transmission electron microscope (TEM), (Carl Zeiss Inc., Jena, Germany) was used with an accelerating voltage of 100 kV. Samples were first dispersed in water and then collected using carbon-film-covered copper grids for analysis. The powder X-ray diffraction (XRD) patterns were examined on a model X’PertPro diffractometer (Panalytical, Almelo, The Netherlands) using Cu Ka radiation (wavelength = 1.54 Å). The data were collected over a range of 10–80° 2h with a step size of 0.01°, nominal time per step of 2 s and slit width 5 nm. Magnetic measurements were carried out using a vibrating sample magnetometer (VSM) model MDKFD (Danesh Pajohan Kavir Co. Kashan, Iran).
2.2. Preparation of Fe3O4 magnetic nanoparticles The preparation of Fe3O4 magnetic nanoparticles was based on dissolving FeCl36H2O (11.68 g) and FeCl24H2O (4.30 g) in 200 mL deionized water. Then, this solution was stirred with mechanical stirrer (1000 rpm) at 80 °C for 30 min. Nitrogen gas was continually bubbled through this solution to expel oxygen. Following that, 25 mL of 25% NH3 was rapidly added to the solution. After that, the color of bulk solution changed from orange to black immediately. The magnetite precipitates were collected by a magnet after
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Fig. 1. Effect of extraction parameters on the extraction efficiency: (A) pH, (B) type and concentration of eluent, (C) eluent volume, (D) nanoadsorbent amount, (E) ultrasonication time and (F) sample volume; The concentration of Bi(III) and Pb(II) were 0.05 ng mL 1 and 0.3 ng mL 1, N = 3.
washing several times with deionized water and then with ethanol. Finally, they were dried in oven at 80 °C for 18 h.
collected by a magnet, rinsed with deionized water, ethanol and dried in the oven at 80 °C for 8 h.
2.3. SiO2 coating of the Fe3O4 magnetic nanoparticles 2.4. Surface modification of core–shell Fe3O4@silica with AAAPTS To protect the magnetic core by the silica film and prepare core–shell magnetic nanoparticles, the as-prepared Fe3O4 (0.5 g) were dispersed in a solution composed of 80 mL ethanol and 20 mL double distilled water by sonicating for 30 min. Then, 5 mL ammonia solution (25 wt%) and 4 mL TEOS were added sequentially. The resulting suspension was stirred and allowed to react for 24 h at room temperature. Finally, the product was
The core–shell Fe3O4@silica nanoparticles (600 mg) were suspended in 80 ml of dry toluene under nitrogen atmosphere. After the addition of AAAPTS (4 mL), the mixture was refluxed at 80 °C for 24 h. The resulting product, as adsorbent, was collected with a magnet, washed with dry toluene, deionized water and ethanol and then dried at room temperature.
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Fig. 2. FT-IR spectra of (A) Fe3O4, (B) Fe3O4@SiO2, (C) AAAPTS and (D) Fe3O4@SiO2@AAAPTS nanoparticles.
Fig. 3. FE-SEM (A1 & A2) and TEM (B1 & B2) images of the nanoadsorbent particles.
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Fig. 4. XRD patterns of (A) Fe3O4, (B) Fe3O4@SiO2 and (C) Fe3O4@SiO2@AAAPTS nanoparticles.
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structures that plays an important role in the enhancement of the adsorption capacity. The TEM images showed that these nanoparticles had entrapped in the silica shell successfully. Also, the diameter of the magnetic core is lower than 50 nm.
Fig. 5. VSM curves of (A) Fe3O4, (B) Fe3O4@SiO2 and (C) Fe3O4@SiO2@AAAPTS nanoparticles.
2.5. Magnetic solid-phase extraction procedure MSPE was carried out as follows. A portion of 25 mL sample solutions containing 0.05 ng mL 1 Bi(III) and 0.3 ng mL 1 Pb(II) were transferred into a 100 mL glass flask and the pH was adjusted to 6.5 using HCl solution. Then, 250 mg of the synthesized Fe3O4@SiO2@AAAPTS was added and the mixture was ultrasonicated for 5 min. In this step, the analytes were adsorbed on the adsorbent. Then, a piece of magnet was placed outside the flask to collect adsorbent and the supernatant was decanted directly. In desorption step, 3.0 mL HNO3 (3.0 mol L 1) was added as eluent and ultrasonicated for 5 min. Finally, the magnet was used again to collect the nanoparticles, and the eluent was transferred into a test tube for subsequent ETAAS analysis. 3. Results and discussion 3.1. Characterization of Fe3O4@SiO2@AAAPTS nanoparticles 3.1.1. FT-IR spectroscopy The FT-IR spectrum of Fe3O4 nanoparticles shows the absorption peak at 562 cm 1 which corresponding to the Fe–O vibration (Fig. 2A). The silica shell coated on the surface of magnetite core can be confirmed by the spectrum in Fig. 2B. The bands at 1092 cm 1 and 799 cm 1 are assigned to Si–O–Si vibrations, the peak at 948 cm 1 was related to the vibration of Si–OH group and the absorption peak of Fe3O4 at 573 cm 1 indicated that MNPs is covered by silica layer through experiment. In the spectrum of AAAPTS (Fig. 2C), the peaks at 3292 cm 1 and 1593 cm 1 can be assigned to N–H stretching and bending vibrations, respectively. The two peaks at 2937 cm 1 and 2839 cm 1 are due to asymmetrical and symmetrical C–H stretching vibrations and C–H bending peak is observed at 1462 cm 1. The band at 1194 cm 1 is ascribed to the stretching of the C–N stretching bonds. Another two peaks at 1082 cm 1 and 819 cm 1 might be ascribed to Si–O–Si vibrations. Also, the surface modification of core–shell nanoparticles can be confirmed by FT-IR (Fig. 2D). The two peaks at 468 cm 1 and 576 cm 1 are due to Fe–O–Si and Fe–O stretching vibrations, respectively. 3.1.2. FE-SEM and TEM images The morphological feature of the synthesized Fe3O4@SiO2@ AAAPTS nanoparticles were characterized by FE-SEM and TEM images and shown in different magnification (Fig. 3). The FE-SEM images showed the MNPs have relatively homogeneous and porous
3.1.3. XRD patterns The typical XRD patterns of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@AAAPTS nanoparticles are shown in Fig. 4. The diffraction peaks (2h = 30.2°, 35.5°, 43.1°, 53.4°, 57.1° and 62.8°) related to (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0), can be indexed to face-centered cubic structure of magnetite. Also, board peak at low diffraction angle (2h = 16–28°) which corresponded to the amorphous peak of SiO2 was displayed in Fig. 4B. AAAPTS modified Fe3O4@SiO2 surface can be confirmed from the XRD data (Fig. 4C). The characteristics diffraction peaks that correspond to Fe3O4 and SiO2 can be observed. There also exist other diffraction peaks which can be attributed to the reflection of methoxysilane group in AAAPTS that were overlapped with other peaks. 3.1.4. Magnetic measurements Fig. 5 shows that the saturation magnetization values were 72.3, 44.1, and 38.7 emu g 1 for Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@AAAPTS, respectively. Compared with the Fe3O4, the saturation magnetization of Fe3O4@SiO2@AAAPTS reduced to 38.7 emu g 1, but it is sufficient for magnetic separation with a conventional magnet. 3.2. Optimization of extraction conditions Several experimental variables affecting the extraction recovery of bismuth and lead ions were investigated, including, sample pH, the eluting solvent, the adsorbent amount, ultrasonic time and sample volume. In all optimization experiments one-at-a-time strategy was used. 3.2.1. Effect of pH The sorption ability of bismuth and lead ions by the as-prepared modified MNPs is significantly dependent on the pH value of the aqueous solution. The influence of pH on the extraction recovery of target ions was tested in the range 3–8, when the other parameters were kept constant. Fig. 1A shows the recovery percentage increased along with increasing pH value from 3 to 6.5 and maximum recovery was obtained at pH 6.5. When the pH was further enhanced from 6.5 to 8, the recovery percentage decreased silently. Because, the precipitation reactions may occur for Pb(II) and Bi(III) ions. Therefore, pH 6.5 was selected in the following experiments. 3.2.2. Effect of eluent The effect of type and volume of eluent on the recovery of Bi(III) and Pb(II) was investigated. As can be seen from Fig. 1A, the sorption of these ions on the adsorbent at acidic solution is low. It means that desorption can be done in this media. Therefore, various acidic solutions were used as eluent and the results showed that HNO3 with the concentration of 3 mol L 1 was the best ones (Fig. 1B). Also, the eluent should elute analytes quantitatively in a small volume. Thus, the volume range of 0.5–5 mL was tested and the results were shown in Fig. 1C. Finally, 3 mL of 3 mol L 1 HNO3 was chosen for the elution. 3.2.3. Effect of Fe3O4@SiO2@AAAPTS amount In the MSPE technique, the amount of magnetic adsorbent is one of the main factors effecting on the extraction of the analytes. Hence, this parameter was studied in the range 0.005–0.1 g. the results indicate the recovery percentage increased with an increase in the adsorbent content which could be due to the availability of more sorption sites and larger surface area. After a certain value
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Table 2 Effect of coexisting ions. Foreign ion +
Na Cl K+ NO3 NH+4 CH3COO Ca2+ Zn2+ Cd2+ Al3+ Co2+ Mo6+ Cr3+ Fe3+ Fe2+ EDTA
Table 4 Determination of bismuth and lead ions in real samples.
Foreign ion/Pb ratio
Foreign ion/Bi ratio
Recovery (%)a
2000 2000 2000 2000 2000 2000 1000 1000 1000 1000 1000 1000 1000 1000 1000 500
2000 2000 2000 1000 700 1000 1000 650 1000 1000 550 1000 850 1000 1000 400
100.8 ± 1.2 100.5 ± 3.4 98.2 ± 3.9 97.8 ± 2.3 98.8 ± 3.6 96.6 ± 5.2 99.1 ± 3.6 98.9 ± 2.8 97.4 ± 3.7 99.6 ± 3.3 96.0 ± 2.6 97.7 ± 4.5 102.1 ± 3.6 96.8 ± 4.9 98.9 ± 4.5 95.4 ± 3.2
Samples
Tap waterb
Well waterc
Human hair (pg g -1)
a
Under optimum conditions. a Mean ± standard deviation (N = 3).
b c
(0.025 g), no further increase in percent occurred as an increase in adsorbent content (Fig. 1D). So, 0.025 g was used in the all subsequent experiments.
3.2.4. Effect of ultrasonication time In this method, for both adsorption and desorption, ultrasonic treatment times in the range 1–20 min were investigated. The experimental results indicated that 5 min was sufficient for achieving quantitative recovery of bismuth and lead ions for both adsorption and desorption (Fig. 1E).
3.2.5. Effect of sample volume The sample volume is an important parameter to obtain a high enrichment factor. Experimental analysis showed (Fig. 1F) that, when sample volume was 600 mL, quantitative recovery was obtained and theoretical enrichment factors were 200 for both target ions. But in experimental state, enrichment factors were 152 and 163 for Bi(III) and Pb(II), respectively.
Spiked (ng L 1)
Founda (ng L
1
Recovery (%)
Bi
Pb
Bi
Pb
Bi
Pb
0.0 20.0 40.0 80.0 0.0 20.0 40.0 80.0 0.0
0.0 30.0 60.0 90.0 0.0 30.0 60.0 90.0 0.0
8.1 ± 0.05 28.2 ± 0.11 48.6 ± 0.15 87.7 ± 0.19 8.9 ± 0.04 29.1 ± 0.12 47.5 ± 0.13 88.5 ± 0.22 9.4 ± 0.06
21.0 ± 0.09 52.0 ± 0.16 80.0 ± 0.18 113.0 ± 0.25 23.0 ± 0.14 52.0 ± 0.15 82.0 ± 0.21 114.0 ± 0.26 430.0 ± 0.30
– 100.5 101.3 99.50 – 101.0 96.50 99.50 –
– 103.3 98.30 102.2 – 96.60 98.30 101.1 –
20.0 40.0 80.0
30.0 40.0 60.0
29.1 ± 0.11 49.0 ± 0.14 89.7 ± 0.17
459.2 ± 0.32 469.5 ± 0.31 490.2 ± 0.33
98.50 99.00 100.4
97.30 98.80 100.3
)
Mean ± SD (N = 3). Kerman drinking water, Kerman, Iran. Shahid Bahonar University of Kerman, Kerman, Iran.
3.3. Adsorption capacity The adsorption capacity is an important factor to evaluate the Fe3O4@SiO2@AAAPTS nanoadsorbent. It is the maximum analytes quantity taken up by 1.0 g of synthesized nanoadsorbent. In order to determine this factor, 50 mg of the nanoadsorbent were subjected to several loadings with 25 mL sample solutions containing Bi(III) and Pb(II) with pH = 6.5 and then, followed by the determination of retained analytes using ETAAS. The values of adsorption capacity increased with the increase of initial concentrations of target ions and then it reached a plateau. The static adsorption capacity (13.61 mg g 1 for lead ions and 12.22 mg g 1 for bismuth ions) of the nanoadsorbent was obtained. 3.4. Effect of coexisting ions interference Under optimized conditions, the interference of various cations and anions on the recovery of bismuth and lead ions was investigated. Results obtained showed that Fe3O4@SiO2@AAAPTS is a good
Table 3 Comparison of linear range (LR), limits of detection (LOD) and relative standard deviation (RSD) of this method with other reported methods for preconcentration of bismuth and lead ions. Analytical technique a
FI -SPE-ETAAS FI-CPEb-ICPc-AESd USAEMEe-ICP-OESf SFODMEg-ETVh-ICP-MSi j
SPE-FAAS
MSPE-ETAAS a b c d e f g h i j
1)
Metal ions
LR (lg L
Bi Pb Bi Pb Bi Pb Bi Pb Bi Pb Bi Pb
– – 1–50 – 1–1000 1–1000 0.02–20 0.05–20 – 5–20000 0.003–0.2 0.02–0.7
Flow injection. Cloud point extraction. Inductively coupled plasma. Atomic emission spectroscopy. Ultrasonic-assisted emulsification microextraction. Optical emission spectrometry. Solidified floating organic drop microextraction. Electrothermal vaporization. Mass spectrometry. Flame atomic absorption spectroscopy.
LOD (lg L 0.013 0.0045 0.12 – 0.48 5.6 0.0041 0.017 – 1.0 0.0014 0.0037
1
)
RSD (%)
Refs.
5.3 3.8 2.3 – 1.8 5.6 4.6 4.6 – 3.8 3.6 3.1
[32] [33] [34] [35] [36] This work
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candidate to preconcentration of target analytes without any serious matrix interference in different real samples (Table 2). 3.5. Analytical performance Under optimized conditions, linear range (LR), limits of detection (LODs) and repeatability were studied. The obtained linearity was 0.003–0.200 ng mL 1 for Bi(III) and 0.02–0.700 ng mL 1 for Pb(II). The LODs (defined as 3Sdblank/m, where Sd is the standard deviation of the blank readings for ten replicate analysis and m is the slope of the calibration curve) was 1.4 ng L 1 and 3.7 ng L 1 for bismuth and lead, respectively. Also, the resultant repeatability expressed as relative standard deviations (RSD, N = 8) were calculated as 3.6% and 3.1% for 0.07 ng mL 1 and 0.35 ng mL 1 concentration of Bi(III) and Pb(II), respectively. In Table 3, a comparison of the developed method with the other reported preconcentration methods [32–36] for determination of target analytes was done. As this table shows, the LODs found in the present work are better than other works reported elsewhere. Also, the RSD% and linearity values are comparable with the values reported for other methods. 3.6. Analysis of the real samples The method was applied to the determination of trace amounts of Bi(III) and Pb(II) in a variety of samples. The samples were also analyzed after spiking with different concentrations of bismuth and lead ions with high recoveries. Tap water, well water, and human hair samples were analyzed. The analytical results are presented in Table 4. The results show that the method is suitable for the analysis of real samples. 4. Conclusion Fe3O4@SiO2@AAAPTS nanoparticles with good saturation magnetization have been successfully prepared and used as a novel and effective adsorbent for simultaneous extraction and preconcentration of bismuth and lead ions from aqueous solutions prior to determination by ETAAS. It is a very fast extraction method, because the MNPs have generally high surface area and fast magnetic separation. Ease of operation, high selectivity and sensitivity are other advantages. Also, the combination of MSPE by the as-prepared nanoadsorbent with ETAAS offers significant analytical performance. References [1] A.M. El-Toni, M.A. Habila, M.A. Ibrahim, J.P. Labis, Z.A. ALOthman, Simple and facile synthesis of amino functionalized hollowcore–mesoporous shell silica spheres using anionic surfactant for Pb(II), Cd(II), and Zn(II) adsorption and recovery, Chem. Eng. J. 251 (2014) 441–451. [2] A.K. Das, R. Chakraborty, M.L. Cervera, M. Guardia, Analytical techniques for the determination of bismuth in solid environmental samples, Trends Anal. Chem. 25 (2006) 599–608. [3] N. Yang, H. Sun, Biocoordination chemistry of bismuth: Recent advances, Coord. Chem. Rev. 25 (2007) 2354–2366. [4] A. Nosal-Wiercinska, The kinetics and mechanism of the electroreduction of Bi(III) ions from chlorates (VII) with varied water activity, Electrochim. Acta 55 (2010) 5917–5921. [5] J.A. Reyes-Aguilera, M.P. Gonzalez, R. Navarro, T.I. Saucedo, M. Avila-Rodriguez, Supported liquid membranes (SLM) for recovery of bismuth from aqueous solutions, J. Membr. Sci. 310 (2008) 13–19. [6] S. Itoh, S. Kaneco, K. Ohta, T. Mizuno, Determination of bismuth in environmental samples with Mg–W cell–electrothermal atomic absorption spectrometry, Anal. Chim. Acta 379 (1999) 169–177. [7] S. Hernberg, Lead poisoning in a historical perspective, Am. J. Ind. Med. 38 (2000) 244–254. [8] H. Needleman, Lead poisoning, Annu. Rev. Med. 55 (2004) 209–222. [9] E. Ayranci, O. Duman, Binding of lead ion to bovine serum albumin studied by ion-selective electrode, Protein Pept. Lett. 11 (2004) 331–337.
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