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Preconcentration and separation of ultra-trace beryllium using quinalizarine-modified magnetic microparticles
Analytica Chimica Acta 646 (2009) 123–127
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Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca
Preconcentration and separation of ultra-trace beryllium using quinalizarine-modified magnetic microparticles Parviz Ashtari a,b,∗ , Kemin Wang a , Xiaohai Yang a , Seyed Javad Ahmadi b a State Key Laboratory of Chemo/Biosensing & Chemometrics, Biomedical Engineering Center, College of Chemistry & Chemical Engineering, Hunan University, Changsha 410082, PR China b NFCS, Nuclear Science and Technology Research Institute, PO Box 11365-8486, Tehran, Iran
a r t i c l e
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Article history: Received 4 February 2009 Received in revised form 4 May 2009 Accepted 6 May 2009 Available online 12 May 2009 Keywords: Beryllium Extraction Magnetic microparticles Quinalizarine Separation
a b s t r a c t Magnetically-assisted chemical separation/preconcentration method for the analysis of beryllium from aqueous solutions was developed. According to this method several extractants were coated on certain magnetic microparticles to assist the extraction of beryllium from the aqueous solutions. The influence of different parameters (type and amount of extractant, pH, equilibrium time and ionic strength) was investigated. Also, the interfering effect of various cationic and anionic species on the percent recovery of beryllium was studied. The applied spectrophotometric method showed good linearity and precision at a given wavelength (605.0 nm). Among the extractants used, quinalizarine resulted in almost a full recovery of beryllium at pH 7.4, which was the optimum extraction pH. The equilibrium time of the extraction was 10.0 min. The quantitative re-extraction was carried out by 0.5 M nitric acid. Also, the stability of the extractant-coated magnetic microparticles was 4 cycles (extraction and re-extraction) and the used magnetic microparticles showed good selectivity for beryllium against other cations and anions. Finally, the developed method was applicable for the preconcentration and separation of beryllium from spring water, tap water and certified reference waters. The obtained detection limit was 30 ng L−1 . © 2009 Elsevier B.V. All rights reserved.
1. Introduction Beryllium metal, alloys and salts have attracted much attention in various industrial applications [1–3]. Pure beryllium and its metal alloys with copper, aluminum, magnesium, nickel, zinc, and iron have widely been used for the electrical equipment, electronic instrumentations and structural components of aircrafts, missiles, satellites, rockets, nuclear reactors, missile fuels and instrumental detectors [1,4–7]. Therefore, despite the scarcity of beryllium in earth crust (∼2.8–5.0 g g−1 ) [1,8], its entry into the water supplies are due to the discharges of the above industries. Beryllium and its compounds are very toxic, especially to the lungs, skin, and eyes. So far, no cures have been found for chronic beryllium disease and berylliosis (inhalation of beryllium compounds which produces scarring of the lung tissue) [9,10]. Consequently, the preconcentration and determination of the trace amounts of Be is of much importance. It is desired to develop a simple, effective, reliable and environmentally friendly method for the preconcentration and analysis of the environmental and biological samples. Precipitation [11,12], ion-exchange [3,13,14], sol-
∗ Corresponding author at: NFCS, Nuclear Science and Technology Research Institute, PO Box 11365-8486, Tehran, Iran. Tel.: +98 21 88221128; fax: +98 21 88221128. E-mail address: [email protected] (P. Ashtari). 0003-2670/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2009.05.004
vent extraction [15–19], solid phase extraction [20] and extraction method which continued by fluorescence measurement [21–23] are among the methods reported for the preconcentration and separation of trace amounts of Be. However, there are several main concerns associated with the above methods. They are time consuming, require large amounts of chemical additives and also produce large amounts of secondary wastes [24]. Solvent losses, a need for complex equipments and bulky design are among other problems. Therefore, it is advantageous to seek alternate methods that have overcome such problems. Magnetically-assisted chemical separation (MACS), which was developed by the Argonne National Laboratory (ANL), is based on the preconcentration of target analyte(s) on the relatively small amount of magnetic or magnetizable adsorbents [25]. It uses magnetic nano or microparticles and combines the selective and efficient separation offered by chemical extraction with magnetic recovery of extractant for selective separation of metal ions [24,26], radionuclides and transuranic elements [25,27–30] and organic compounds [31]. In MACS method, there are two ways to bind metal ions onto particle surfaces. The first one is based on the covalent immobilization of complex metal ions on particle surface [32]. Another one is based on the simple physical adsorption of chelators or metal ions on particle surfaces [24–31]. The latter was used in this study. In a separate study, the authors applied suspending extractant-modified magnetic microparticles for the preconcentration and separation of
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copper [33]. In the mentioned study the detail of the method and the advantages were described [33]. In the current study, the effect of different experimental conditions (type and amount of extractant-modified magnetic microparticles, pH, equilibrium time, ionic strength, stripping conditions) on the preconcentration and separation of Be was investigated. In addition, the developed method was used for the preconcentration, separation and determination of nano-gram amounts of spiked Be from tap water and spring water as real samples and aqueous Certified Reference Materials. 2. Materials and methods 2.1. Materials All the chemicals were of analytical-reagent grade and used without any further purification. Double-distilled deionized water (Branstead Co., USA) was used throughout the experiments. Reagent grade quinalizarine (1,2,5,8-tetrahydroxy anthraquinone), 2-thenoyl-trifluoroacetone (TTF), dibenzo-18crown-6 (DB), chrome azurol S (CAS), cetyl pyridinium chloride (CPC), hexamethylene-tetramine (HMT) as buffer, from Merck Chemicals (Germany), were used as received. The magnetic microparticles (1–60 m in diameter) were obtained from Cortex Biochem Inc. (San Leandro, CA, USA) as a 1:1:1 weight ratio of cross-linked polyacrylamide and acrylic acid entrapping charcoal and iron oxide (Fe3 O4 ). The standard stock solution of Be was prepared by dissolving an appropriate amount of BeSO4 ·4H2 O in deionized water. The working solutions were prepared by appropriate dilutions of the stock Be solution using 0.05 M ammonium acetate solution. 2.2. Apparatus All UV–vis absorbance measurements were performed by DU800 spectrophotometer (Beckman, England). Orion pH meter, model 868 digital, equipped with combined glass-Calomel electrodes was used for pH adjustment. A Lab-lines shaker (Lab Wing, Netherlands) was used for shaking the samples. An ED53 Binder oven (MG Scientific, USA) was used to heat the microparticles at 100 ◦ C for 24 h. An ICP-AES, IRIS Advantage 1000 (Thermal Elemental, USA) was used for the determination of major ions (Na, K, Mg, Ca). 2.3. Procedure The microparticles used for the extraction was prepared according to a procedure described previous [33]. 200.0 mg of magnetic microparticles was washed three times with distilled deionized water and twice with ethanol for the removing of preservatives and unbound materials left from the manufacturing process. Then, 100.0 mg of magnetic microparticles was poured into a Teflon beaker. Quinalizarine, TTF and DB were used as extractants. Quinalizarine was dissolved in a 3:7 (v/v) mixture of tetrahydrofuran (THF) and ethanol. TTF and DB were dissolved in ethanol. According to our experiments, while the maximum loading capacities for the quinalizarine was less than 2.5%, those of TTF and DB were both at 5.0% levels. The mixtures were gently stirred using a Teflon rod and solvents were slowly evaporated by the heat of a hair drier for about 30.0 min. Finally, the extractant-modified magnetic microparticles were heated in the same beaker at 100 ◦ C for 24 h to stabilize quinalizarine-modified layer and completely eliminate the residual solvent. The extractions were performed in test tubes containing 200.0 ng Be in 10.0 mL solution of 0.05 M ammonium acetate. The pHs of the solutions were adjusted to the desired level by dropwise
addition of 1.0 M nitric acid and/or 1.0 M ammonium hydroxide as needed. The solutions were added to 5.0 mg extractantmodified and pre-conditioned microparticles and shaken for at least 20.0 min. Then, the test tubes were placed in a magnetic concentrator, where permanent magnet in the wall caused the particles to aggregate on one side of the test tube. Every experiment was repeated at least three times and the results were reported as the mean value of these three experiments. The backextractions were performed by using 3.0 mL of the 0.5 M nitric acid. Be was determined by spectrophotometry at 605.0 nm. The standard solutions containing 50.0, 100.0, 150.0, 200.0 and 400.0 ng Be were used to draw calibration curve of the UV–Visible spectrophotometer. The details are as following; 5.0 mL of the 1.0 M HMT buffer (pH 5.0), 1.0 mL of the 0.1 M EDTA, 0.5 mL of the 0.25% CPC, 0.5 mL of the 0.5% MgSO4 , and 0.5 mL of the 1% CAS were added, respectively, on the mentioned beryllium aqueous solutions. The solutions were diluted with deionized water to 25.0 mL in volumetric flasks and were mixed thoroughly and heated in a water bath (at 60.0 ◦ C) for 10.0 min. Then, mixtures were maintained at room temperature for additional 30.0 min, and the absorbance of standards vs. a blank solution measured at 605.0 nm to obtain the standard curve. The absorbances obtained for the solutions were stable at least for 120.0 min. The calibration curve was linear (Y = 0.003X − 0.007) in the range of 0–400 ng Be in the solution. Good linearity was obtained at the selected wavelength (R2 = 0.9985).
3. Results and discussion 3.1. Effect of type and amount of extractant-modified magnetic microparticles The extraction efficiency of 2% quinalizarine-modified magnetic microparticles (Q-MMP), non-modified magnetic microparticles, 5% 2-thenoyltrifluoroacetone-modified magnetic microparticles (TTF-MMP) and 5% dibenzo-18-crown-6-modified magnetic microparticles (DB-MMP) for quantitative extraction of Be were investigated. Among those microparticles, Q-MMP yielded the highest extraction efficiency under the current experimental conditions (Table 1). The extraction was found to be quantitative at the optimum pH (7.4), when microparticles were loaded with 2% quinalizarine. Hence, subsequent extractions were carried out with 2% Q-MMP. Fig. 1 shows the effect of the amount of the 2% Q-MMP for the quantitative extraction of beryllium. Various amounts of 2% QMMP, 1.0–10.0 mg, were investigated. The extraction was found to be quantitative when ≥3.0 mg microparticles was used. Therefore, subsequent experiments were carried out with the 5.0 mg of 2% QMMP. The equilibrium partition coefficient, Kd , is expressed in Eq.
Table 1 The effect of type of extractant modified on magnetic microparticles on the recovery of Be [5.0 mg of 2% quinalizarine-modified magnetic microparticles (Q-MMP), non-modified magnetic microparticles (Non-mod.), 5% 2-thenoyl-trifluoroacetone-modified magnetic microparticles (TTF-MMP) and 5% dibenzo-18-crown-6-modified magnetic microparticles (DB-MMP) contacted with 10.0 mL aqueous solution, pH 7.4, containing 200.0 ng Be]. Type of magnetic microparticles
Recovery of Bea (%)
Q-MMP Non-mod. TTF-MMP DB-MMP
100.00 (6.30) 90.90 (6.80) 87.50 (4.40) 85.30 (4.90
a
Means of triplicate analysis (%R.S.D.).
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Fig. 1. Effect of the amount of 2% quinalizarine-modified magnetic microparticles (Q-MMP) on the recovery of Be (10.0 mL aqueous solution, pH 7.4, containing 200.0 ng of Be was contacted with 1.0–10.0 mg of 2% Q-MMP).
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Fig. 3. Effect of the equilibrium time on the recovery of Be [5.0 mg of the 2% quinalizarine-modified magnetic microparticles (Q-MMP) contacted with 10.0 mL aqueous solution in pH 7.4 containing 200.0 ng of Be as beryllium sulfate at different time intervals].
(1) as Kd =
(V/m)(Ci − Cf ) Cf
3.3. Effect of equilibrium time (1)
where V/m is the solution volume-to-particle mass ratio and Ci and Cf are the initial and final metal concentrations in solution, respectively. The achieved Kd is higher than 104 mL g−1 . It is the highest Kd values which was achieved for Be in comparing with solvent extraction [34], cation exchange [13] and liquid anion exchange [35]. 3.2. Effect of pH Effect of pH on the extraction recovery of Be was investigated in the range 2.0–9.5 using 5.0 mg 2% Q-MMP. The results are shown in Fig. 2. The extraction efficiency was nearly constant and quantitative in the pH range of 6.8–7.8. Hence, the pH of 7.4 was chosen as the optimum pH for the subsequent extraction experiments. At this pH, quinalizarine exists as an anion and Be as a cation (Be2+ or BeOH+ ) making the two species attract each other and build a coordinate-covalent bond [20]. This is the first time that quantitative extraction of Be is reported from a neutral to slightly alkaline solution (pH’s around 7.0). Most of the reported separation/preconcentration studies are in acidic media [16,20,34–36].
The effect of equilibrium time on the efficiency of the extraction was investigated by shaking the suspension of the 5.0 mg 2% Q-MMP and Be aqueous solutions in the experimental conditions. The experiments were carried out at 1.0, 3.0, 5.0, 10.0, 20.0, 40.0, and 60.0 min intervals and the recovery percentages of Be were determined, respectively. According to the results of this experiment (Fig. 3), the extractions are completed in 10.0 min. To have more reliable results, all extractions in this study were performed for 20.0 min. 3.4. Effect of ionic strength The influence of ionic strength (electrolyte concentration) on the extraction efficiency of Be, using 2% Q-MMP, was investigated in aqueous solutions containing various concentrations of potassium nitrate (0.02–2.0 M). The quantitative extraction of beryllium was obtained in the 0.02–1.0 M KNO3 concentrations range. Even in the presence of 2.0 M KNO3 , the extraction efficiency was 85.8% indicating the specific preference of the Q-MMP towards beryllium rather than potassium. Therefore, this method could be applied for the selective separation of Be from highly saline solutions. This also could be concluded from the high Kd value (Kd > 104 mL g−1 ). 3.5. Maximum capacity of the 2% Q-MMP The 2% Q-MMP in 5.0 mg portions were contacted with 10.0 mL aqueous solutions containing 1.0 g Be at optimal extraction conditions. The maximum extraction capacity for the 5.0 mg of 2% Q-MMP was found 661.0 ± 8.9 ng using the back-extraction method explained in the next section. 3.6. Stripping of the extracted beryllium
Fig. 2. Effect of pH on the recovery of Be [5.0 mg of the 2% quinalizarine-modified magnetic microparticles (Q-MMP) contacted with 10.0 mL aqueous solution containing 200.0 ng Be as beryllium sulfate in 20.0 min equilibrium time].
Since high extraction efficiency was achieved by the current method, an efficient back-extraction stage [24,25] for the stripping off Be from Q-MMP is required, several stripping solutions including 0.1, 0.5 and 1.0 M ammonia; 0.01, 0.1 and 1.0 M sulfo-salicylic acid; 0.1, 0.5 and 1.0 M nitric acid and water were examined. However, in this study, the 0.5 M nitric acid was the best eluent. In the presence of 0.5 M nitric acid, recovery of Be from modified microparticles is quantitative. No adverse effects have been found for nitric acid on the magnetic microparticles [37] or quinalizarine [20].
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Table 2 Effect of maximum levels of interfering ions on the quantitative recovery of Be [5.0 mg of the 2% quinalizarine-modified magnetic microparticles (Q-MMP) in 10.0 mL aqueous solutions containing 200.0 ng of Be (BeSO4 ), at pH 7.4 and different amounts of each interfering ion at optimal experimental condition]. Ions
Source
Amount (mg)
Recovery of Be (%)a
Mg2+ Zn2+ Co2+ Ni2+ Pb2+ Ca2+ Cd2+ Cu2+ Fe3+ Cr3+ MoO4 2− Na+ Ba2+ Li+ EDTA2− Mn2+
MgSO4 ·7H2 O Zn(CH3 COO)2 ·2H2 O CoCl2 ·6H2 O NiSO4 ·6H2 O Pb(NO3 )2 CaCl2 CdSO4 ·8/3H2 O Cu(NO3 )2 ·3H2 O FeCl3 ·6H2 O CrCl3 ·6H2 O Na2 MoO4 NaCl BaCl2 ·2H2 O LiClO4 ·3H2 O Na2 EDTA MnSO4 ·H2 O
2.0 2.0 2.0 0.8 0.4 1.6 0.2 0.05 1.6 0.2 0.4 2.0 2.0 2.0 10−4 M 0.2
101.9 (2.8) 94.9 (3.3) 102.4 (3.6) 99.3 (3.9) 98.0 (4.0) 96.4 (2.8) 100.4 (3.2) 97.5 (3.5) 99.3 (3.7) 104.8 (4.1) 97.7 (2.6) 100 (2.0) 103.1 (2.7) 102.6 (4.1) 102.2 (2.5) 96.5 (2.7)
a
Means of triplicate analysis (%R.S.D.).
In a complementary experiment, the effect of volume of 0.5 M nitric acid in the quantitative stripping of Be from the 2% Q-MMP was investigated. The stripping was conducted using 1.0, 2.0, 2.5, 3.0, 4.0 and 5.0 mL portions of nitric acid. A 2.5 mL solution of nitric acid 0.5 M was sufficient for the full stripping off the Be. However, to ensure complete recovery, stripping was carried out using 3.0 mL 0.5 M nitric acid solutions. 3.7. Stability of the modified microparticles in experimental conditions Stability of the 2% Q-MMP under experimental conditions was examined by using 5.0 mg of 2% Q-MMP in several extraction/stripping conditions. After four cycles of extraction and back-extraction, some darkness appeared in the solution surface that could not be removed from the solution even by centrifugation (due to the use of sonication). Therefore, the stability of the 2% Q-MMP is limited to only 4 cycles of extraction/back-extraction. 3.8. Selectivity of the extraction Selective separation and determination of Be from its binary mixtures with diverse metal ions were investigated by using 2% Q-MMP and the aqueous solutions containing 200.0 ng of Be in the presence of mg levels of interfering ions and complexing agents (Table 2). According to the results, the recovery of Be at ng level was also quantitative in the presence of mg levels of the interfering diverse ions as their chloride, nitrate, sulfate and perchlorate salts. The selectivity of the current method is much higher than that of the solid phase extraction, which was reported by Yamini et al. [20]. In the current study, there was no need to use a masking agent (thiourea) to separate Fe3+ from Be (as Be2+ ). The amounts of the interfering ions for Mg2+ and Ca2+ were 40 and 32 times, respectively, higher than those reported by Yamini et al. [20]. Although in their study the separation efficiency was dropped to 39% [20] in the
presence of EDTA when using solid phase extraction for the recovery of Be, no such effect was found in our study when using EDTA at 270 times higher concentration than that of their study. Also, the selectivity of the current method is compared against the standardized portable fluorescence method reported, where potentially interfering metals were used at ≥400-fold molar excess to beryllium (Agrawal et al. [21,22]). By converting the molar ratio to mg and comparing the reported selectivity values, it can be concluded that the amounts of the interfering ions used in our study for Li, Co, Fe, Zn and Ni, are respectively 30.0, 4.0, 3.0, 2.5 and 1.5 times, higher than those of their study. However, the selectivity for Ca, Pb and Cu in this study are respectively decreased to 0.9, 0.4 and 0.1 of those report. 3.9. The analytical performance of the new method for the analysis of real samples For assessing the capability of the method for the recovery of Be from real samples containing varying amounts of diverse ions, two different real samples (tap water and spring water) were chosen and the method was applied for the preconcentration, separation and quantification of spiked Be (200.0 ng in 100.0 mL water samples). Fifteen mg Q-MMP was used. The water samples were collected from Hunan University area located on the west of Changsha City (Yuelu Shan) in the Hunan Province of the Peoples Republic of China. Table 3 shows the complementary characteristics and recovery percent of spiked Be. Results show that Be recovery was almost quantitative. Detection limit (LOD) of the current method under optimal experimental conditions was obtained at 30.0 ng L−1 , which is better than those obtained by solid phase extraction–flame atomic absorption, 200 ng L−1 [20] and 300 ng L−1 [38], chelation ion chromatography 35 g L−1 [39], adsorptive stripping voltammetry 30 ng L−1 [40], although, the detection limit of the method is less than the expensive and instrumental preconcentration and determination method such as extraction and GF-AAS 0.6 ng L−1 [4], 2.3 ng L−1 [16] and fluorometric determination 20 ng L−1 [41]. 3.10. Certified reference material analysis For approving the capability of the studied method, a mixture of two aqueous environmental Certified Reference Materials (GSBZ 50009-88 and GSB 07-1178-2000) from National Certified Reference Materials (P.R. China) was prepared and analyzed by the introduced method. The prepared sample contained 20.0 g L−1 Be along with Cu, Pb, Zn, Cd, Ni, Cr, K, Na, Ca, Mg at 1.13, 1.56, 0.390, 0.129, 0.648, 0.791, 4.60, 10.0, 20.0, 5.1 mg L−1 levels, respectively. The obtained recovery percent for Be was 99.96 ± 5.22% (n = 5). Therefore, the accuracy and the precision of the introduced method obtained in this study are in good agreement with the reference data. 4. Conclusions The introduced method for the recovery of Be based on Q-MMP as extractant shows good capability for the selective and quantitative separation and preconcentration of Be from the aqueous samples without any filtration step. Also, the applied photometric
Table 3 Characterization and recovery of the spiked Be on the different water samples used at optimum experimental conditions [100.0 mL of spring and tap water containing 200.0 ng Be, at pH 7.4 contacted with 15.0 mg of 2% quinalizarine-modified magnetic microparticles (Q-MMP) at the optimum experimental conditions]. Sample
pH
Conductivity (S cm−1 )
Ca (ppm)
K (ppm)
Mg (ppm)
Na (ppm)
Recoverya (%w/w)
Spring water Tap water
6.32 6.48
78.6 221
7.50 35.8
0.97 2.27
3.97 3.92
0.56 3.65
94.8 (1.7) 97.1 (1.6)
a
Means of triplicate analysis (%R.S.D.).
P. Ashtari et al. / Analytica Chimica Acta 646 (2009) 123–127
procedure showed good precision in comparison to other instrumental analytical methods such as flame and electrothermal atomic absorption, ion chromatography and stripping voltammetry. The results also showed that the selectivity of the extraction relies on the modification of magnetic microparticles with quinalizarine. Such principle was developed by the ANL as an environmentally friendly method for treatment and remediation of waste [25]. Then the introduced principles were applied for the selective separation of metal ions, radionuclides and organic compounds [24–30]. This method was also applied by the current authors for the selective and quantitative separation of copper [33]. Therefore, this method can potentially be applied as a fast and simple procedure for the recovery and analysis of metal ions specifically and other compounds in general. Significant decrease in the consumption level of chemical reagents (solvent and extractant) is another advantage, which renders this as an environmentally friendly method for the fast preconcentration and separation purposes. Acknowledgments This work was supported in part by the National Key Basic Research Program of China (2002CB513110), Key Technologies Research and Development Program (2003BA310A16), Key Project of Natural Science Foundation of China (90606003), Natural Science Foundation of China (20475015), and China National Key Projects (2005EP090026). The authors would also like to appreciate the NSTRI (Nuclear Science and Technology Research Institute) and Ministry of Science, Research and Technology of Iran for the scholarship and financial support. Also special thanks go to Dr. K. Rezaei from the University of Tehran for editing the manuscript. References [1] M.B. Robert, O. Mark, Beryllium and Beryllium Compounds. Concise International Chemical Assessment Document 32, World Health Organization, Geneva, 2001, pp. 1–11. [2] Reference library at web site: www.espi-metals.com/metals (2009-01-27). [3] D.R. McAlister, E.P. Horwitz, Talanta 67 (2005) 873. [4] T. Okutani, Y. Tsuruta, A. Sakuragawa, Anal. Chem. 65 (1993) 1273. [5] A.E. Greenberg, L.S. Clesceri, A.D. Eaton, APHA, Standard Methods for the Examination of Water and Wastewater, 18th ed., Washington, DC, 1992, pp. 3–53. [6] Toxicological Review of Beryllium and Compounds (CAS No.7440-41-7), U.S. Environmental Protection Agency (EPA/635/R-98/008), Washington, DC, 1998.
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Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca
Preconcentration and separation of ultra-trace beryllium using quinalizarine-modified magnetic microparticles Parviz Ashtari a,b,∗ , Kemin Wang a , Xiaohai Yang a , Seyed Javad Ahmadi b a State Key Laboratory of Chemo/Biosensing & Chemometrics, Biomedical Engineering Center, College of Chemistry & Chemical Engineering, Hunan University, Changsha 410082, PR China b NFCS, Nuclear Science and Technology Research Institute, PO Box 11365-8486, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 4 February 2009 Received in revised form 4 May 2009 Accepted 6 May 2009 Available online 12 May 2009 Keywords: Beryllium Extraction Magnetic microparticles Quinalizarine Separation
a b s t r a c t Magnetically-assisted chemical separation/preconcentration method for the analysis of beryllium from aqueous solutions was developed. According to this method several extractants were coated on certain magnetic microparticles to assist the extraction of beryllium from the aqueous solutions. The influence of different parameters (type and amount of extractant, pH, equilibrium time and ionic strength) was investigated. Also, the interfering effect of various cationic and anionic species on the percent recovery of beryllium was studied. The applied spectrophotometric method showed good linearity and precision at a given wavelength (605.0 nm). Among the extractants used, quinalizarine resulted in almost a full recovery of beryllium at pH 7.4, which was the optimum extraction pH. The equilibrium time of the extraction was 10.0 min. The quantitative re-extraction was carried out by 0.5 M nitric acid. Also, the stability of the extractant-coated magnetic microparticles was 4 cycles (extraction and re-extraction) and the used magnetic microparticles showed good selectivity for beryllium against other cations and anions. Finally, the developed method was applicable for the preconcentration and separation of beryllium from spring water, tap water and certified reference waters. The obtained detection limit was 30 ng L−1 . © 2009 Elsevier B.V. All rights reserved.
1. Introduction Beryllium metal, alloys and salts have attracted much attention in various industrial applications [1–3]. Pure beryllium and its metal alloys with copper, aluminum, magnesium, nickel, zinc, and iron have widely been used for the electrical equipment, electronic instrumentations and structural components of aircrafts, missiles, satellites, rockets, nuclear reactors, missile fuels and instrumental detectors [1,4–7]. Therefore, despite the scarcity of beryllium in earth crust (∼2.8–5.0 g g−1 ) [1,8], its entry into the water supplies are due to the discharges of the above industries. Beryllium and its compounds are very toxic, especially to the lungs, skin, and eyes. So far, no cures have been found for chronic beryllium disease and berylliosis (inhalation of beryllium compounds which produces scarring of the lung tissue) [9,10]. Consequently, the preconcentration and determination of the trace amounts of Be is of much importance. It is desired to develop a simple, effective, reliable and environmentally friendly method for the preconcentration and analysis of the environmental and biological samples. Precipitation [11,12], ion-exchange [3,13,14], sol-
∗ Corresponding author at: NFCS, Nuclear Science and Technology Research Institute, PO Box 11365-8486, Tehran, Iran. Tel.: +98 21 88221128; fax: +98 21 88221128. E-mail address: [email protected] (P. Ashtari). 0003-2670/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2009.05.004
vent extraction [15–19], solid phase extraction [20] and extraction method which continued by fluorescence measurement [21–23] are among the methods reported for the preconcentration and separation of trace amounts of Be. However, there are several main concerns associated with the above methods. They are time consuming, require large amounts of chemical additives and also produce large amounts of secondary wastes [24]. Solvent losses, a need for complex equipments and bulky design are among other problems. Therefore, it is advantageous to seek alternate methods that have overcome such problems. Magnetically-assisted chemical separation (MACS), which was developed by the Argonne National Laboratory (ANL), is based on the preconcentration of target analyte(s) on the relatively small amount of magnetic or magnetizable adsorbents [25]. It uses magnetic nano or microparticles and combines the selective and efficient separation offered by chemical extraction with magnetic recovery of extractant for selective separation of metal ions [24,26], radionuclides and transuranic elements [25,27–30] and organic compounds [31]. In MACS method, there are two ways to bind metal ions onto particle surfaces. The first one is based on the covalent immobilization of complex metal ions on particle surface [32]. Another one is based on the simple physical adsorption of chelators or metal ions on particle surfaces [24–31]. The latter was used in this study. In a separate study, the authors applied suspending extractant-modified magnetic microparticles for the preconcentration and separation of
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copper [33]. In the mentioned study the detail of the method and the advantages were described [33]. In the current study, the effect of different experimental conditions (type and amount of extractant-modified magnetic microparticles, pH, equilibrium time, ionic strength, stripping conditions) on the preconcentration and separation of Be was investigated. In addition, the developed method was used for the preconcentration, separation and determination of nano-gram amounts of spiked Be from tap water and spring water as real samples and aqueous Certified Reference Materials. 2. Materials and methods 2.1. Materials All the chemicals were of analytical-reagent grade and used without any further purification. Double-distilled deionized water (Branstead Co., USA) was used throughout the experiments. Reagent grade quinalizarine (1,2,5,8-tetrahydroxy anthraquinone), 2-thenoyl-trifluoroacetone (TTF), dibenzo-18crown-6 (DB), chrome azurol S (CAS), cetyl pyridinium chloride (CPC), hexamethylene-tetramine (HMT) as buffer, from Merck Chemicals (Germany), were used as received. The magnetic microparticles (1–60 m in diameter) were obtained from Cortex Biochem Inc. (San Leandro, CA, USA) as a 1:1:1 weight ratio of cross-linked polyacrylamide and acrylic acid entrapping charcoal and iron oxide (Fe3 O4 ). The standard stock solution of Be was prepared by dissolving an appropriate amount of BeSO4 ·4H2 O in deionized water. The working solutions were prepared by appropriate dilutions of the stock Be solution using 0.05 M ammonium acetate solution. 2.2. Apparatus All UV–vis absorbance measurements were performed by DU800 spectrophotometer (Beckman, England). Orion pH meter, model 868 digital, equipped with combined glass-Calomel electrodes was used for pH adjustment. A Lab-lines shaker (Lab Wing, Netherlands) was used for shaking the samples. An ED53 Binder oven (MG Scientific, USA) was used to heat the microparticles at 100 ◦ C for 24 h. An ICP-AES, IRIS Advantage 1000 (Thermal Elemental, USA) was used for the determination of major ions (Na, K, Mg, Ca). 2.3. Procedure The microparticles used for the extraction was prepared according to a procedure described previous [33]. 200.0 mg of magnetic microparticles was washed three times with distilled deionized water and twice with ethanol for the removing of preservatives and unbound materials left from the manufacturing process. Then, 100.0 mg of magnetic microparticles was poured into a Teflon beaker. Quinalizarine, TTF and DB were used as extractants. Quinalizarine was dissolved in a 3:7 (v/v) mixture of tetrahydrofuran (THF) and ethanol. TTF and DB were dissolved in ethanol. According to our experiments, while the maximum loading capacities for the quinalizarine was less than 2.5%, those of TTF and DB were both at 5.0% levels. The mixtures were gently stirred using a Teflon rod and solvents were slowly evaporated by the heat of a hair drier for about 30.0 min. Finally, the extractant-modified magnetic microparticles were heated in the same beaker at 100 ◦ C for 24 h to stabilize quinalizarine-modified layer and completely eliminate the residual solvent. The extractions were performed in test tubes containing 200.0 ng Be in 10.0 mL solution of 0.05 M ammonium acetate. The pHs of the solutions were adjusted to the desired level by dropwise
addition of 1.0 M nitric acid and/or 1.0 M ammonium hydroxide as needed. The solutions were added to 5.0 mg extractantmodified and pre-conditioned microparticles and shaken for at least 20.0 min. Then, the test tubes were placed in a magnetic concentrator, where permanent magnet in the wall caused the particles to aggregate on one side of the test tube. Every experiment was repeated at least three times and the results were reported as the mean value of these three experiments. The backextractions were performed by using 3.0 mL of the 0.5 M nitric acid. Be was determined by spectrophotometry at 605.0 nm. The standard solutions containing 50.0, 100.0, 150.0, 200.0 and 400.0 ng Be were used to draw calibration curve of the UV–Visible spectrophotometer. The details are as following; 5.0 mL of the 1.0 M HMT buffer (pH 5.0), 1.0 mL of the 0.1 M EDTA, 0.5 mL of the 0.25% CPC, 0.5 mL of the 0.5% MgSO4 , and 0.5 mL of the 1% CAS were added, respectively, on the mentioned beryllium aqueous solutions. The solutions were diluted with deionized water to 25.0 mL in volumetric flasks and were mixed thoroughly and heated in a water bath (at 60.0 ◦ C) for 10.0 min. Then, mixtures were maintained at room temperature for additional 30.0 min, and the absorbance of standards vs. a blank solution measured at 605.0 nm to obtain the standard curve. The absorbances obtained for the solutions were stable at least for 120.0 min. The calibration curve was linear (Y = 0.003X − 0.007) in the range of 0–400 ng Be in the solution. Good linearity was obtained at the selected wavelength (R2 = 0.9985).
3. Results and discussion 3.1. Effect of type and amount of extractant-modified magnetic microparticles The extraction efficiency of 2% quinalizarine-modified magnetic microparticles (Q-MMP), non-modified magnetic microparticles, 5% 2-thenoyltrifluoroacetone-modified magnetic microparticles (TTF-MMP) and 5% dibenzo-18-crown-6-modified magnetic microparticles (DB-MMP) for quantitative extraction of Be were investigated. Among those microparticles, Q-MMP yielded the highest extraction efficiency under the current experimental conditions (Table 1). The extraction was found to be quantitative at the optimum pH (7.4), when microparticles were loaded with 2% quinalizarine. Hence, subsequent extractions were carried out with 2% Q-MMP. Fig. 1 shows the effect of the amount of the 2% Q-MMP for the quantitative extraction of beryllium. Various amounts of 2% QMMP, 1.0–10.0 mg, were investigated. The extraction was found to be quantitative when ≥3.0 mg microparticles was used. Therefore, subsequent experiments were carried out with the 5.0 mg of 2% QMMP. The equilibrium partition coefficient, Kd , is expressed in Eq.
Table 1 The effect of type of extractant modified on magnetic microparticles on the recovery of Be [5.0 mg of 2% quinalizarine-modified magnetic microparticles (Q-MMP), non-modified magnetic microparticles (Non-mod.), 5% 2-thenoyl-trifluoroacetone-modified magnetic microparticles (TTF-MMP) and 5% dibenzo-18-crown-6-modified magnetic microparticles (DB-MMP) contacted with 10.0 mL aqueous solution, pH 7.4, containing 200.0 ng Be]. Type of magnetic microparticles
Recovery of Bea (%)
Q-MMP Non-mod. TTF-MMP DB-MMP
100.00 (6.30) 90.90 (6.80) 87.50 (4.40) 85.30 (4.90
a
Means of triplicate analysis (%R.S.D.).
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Fig. 1. Effect of the amount of 2% quinalizarine-modified magnetic microparticles (Q-MMP) on the recovery of Be (10.0 mL aqueous solution, pH 7.4, containing 200.0 ng of Be was contacted with 1.0–10.0 mg of 2% Q-MMP).
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Fig. 3. Effect of the equilibrium time on the recovery of Be [5.0 mg of the 2% quinalizarine-modified magnetic microparticles (Q-MMP) contacted with 10.0 mL aqueous solution in pH 7.4 containing 200.0 ng of Be as beryllium sulfate at different time intervals].
(1) as Kd =
(V/m)(Ci − Cf ) Cf
3.3. Effect of equilibrium time (1)
where V/m is the solution volume-to-particle mass ratio and Ci and Cf are the initial and final metal concentrations in solution, respectively. The achieved Kd is higher than 104 mL g−1 . It is the highest Kd values which was achieved for Be in comparing with solvent extraction [34], cation exchange [13] and liquid anion exchange [35]. 3.2. Effect of pH Effect of pH on the extraction recovery of Be was investigated in the range 2.0–9.5 using 5.0 mg 2% Q-MMP. The results are shown in Fig. 2. The extraction efficiency was nearly constant and quantitative in the pH range of 6.8–7.8. Hence, the pH of 7.4 was chosen as the optimum pH for the subsequent extraction experiments. At this pH, quinalizarine exists as an anion and Be as a cation (Be2+ or BeOH+ ) making the two species attract each other and build a coordinate-covalent bond [20]. This is the first time that quantitative extraction of Be is reported from a neutral to slightly alkaline solution (pH’s around 7.0). Most of the reported separation/preconcentration studies are in acidic media [16,20,34–36].
The effect of equilibrium time on the efficiency of the extraction was investigated by shaking the suspension of the 5.0 mg 2% Q-MMP and Be aqueous solutions in the experimental conditions. The experiments were carried out at 1.0, 3.0, 5.0, 10.0, 20.0, 40.0, and 60.0 min intervals and the recovery percentages of Be were determined, respectively. According to the results of this experiment (Fig. 3), the extractions are completed in 10.0 min. To have more reliable results, all extractions in this study were performed for 20.0 min. 3.4. Effect of ionic strength The influence of ionic strength (electrolyte concentration) on the extraction efficiency of Be, using 2% Q-MMP, was investigated in aqueous solutions containing various concentrations of potassium nitrate (0.02–2.0 M). The quantitative extraction of beryllium was obtained in the 0.02–1.0 M KNO3 concentrations range. Even in the presence of 2.0 M KNO3 , the extraction efficiency was 85.8% indicating the specific preference of the Q-MMP towards beryllium rather than potassium. Therefore, this method could be applied for the selective separation of Be from highly saline solutions. This also could be concluded from the high Kd value (Kd > 104 mL g−1 ). 3.5. Maximum capacity of the 2% Q-MMP The 2% Q-MMP in 5.0 mg portions were contacted with 10.0 mL aqueous solutions containing 1.0 g Be at optimal extraction conditions. The maximum extraction capacity for the 5.0 mg of 2% Q-MMP was found 661.0 ± 8.9 ng using the back-extraction method explained in the next section. 3.6. Stripping of the extracted beryllium
Fig. 2. Effect of pH on the recovery of Be [5.0 mg of the 2% quinalizarine-modified magnetic microparticles (Q-MMP) contacted with 10.0 mL aqueous solution containing 200.0 ng Be as beryllium sulfate in 20.0 min equilibrium time].
Since high extraction efficiency was achieved by the current method, an efficient back-extraction stage [24,25] for the stripping off Be from Q-MMP is required, several stripping solutions including 0.1, 0.5 and 1.0 M ammonia; 0.01, 0.1 and 1.0 M sulfo-salicylic acid; 0.1, 0.5 and 1.0 M nitric acid and water were examined. However, in this study, the 0.5 M nitric acid was the best eluent. In the presence of 0.5 M nitric acid, recovery of Be from modified microparticles is quantitative. No adverse effects have been found for nitric acid on the magnetic microparticles [37] or quinalizarine [20].
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Table 2 Effect of maximum levels of interfering ions on the quantitative recovery of Be [5.0 mg of the 2% quinalizarine-modified magnetic microparticles (Q-MMP) in 10.0 mL aqueous solutions containing 200.0 ng of Be (BeSO4 ), at pH 7.4 and different amounts of each interfering ion at optimal experimental condition]. Ions
Source
Amount (mg)
Recovery of Be (%)a
Mg2+ Zn2+ Co2+ Ni2+ Pb2+ Ca2+ Cd2+ Cu2+ Fe3+ Cr3+ MoO4 2− Na+ Ba2+ Li+ EDTA2− Mn2+
MgSO4 ·7H2 O Zn(CH3 COO)2 ·2H2 O CoCl2 ·6H2 O NiSO4 ·6H2 O Pb(NO3 )2 CaCl2 CdSO4 ·8/3H2 O Cu(NO3 )2 ·3H2 O FeCl3 ·6H2 O CrCl3 ·6H2 O Na2 MoO4 NaCl BaCl2 ·2H2 O LiClO4 ·3H2 O Na2 EDTA MnSO4 ·H2 O
2.0 2.0 2.0 0.8 0.4 1.6 0.2 0.05 1.6 0.2 0.4 2.0 2.0 2.0 10−4 M 0.2
101.9 (2.8) 94.9 (3.3) 102.4 (3.6) 99.3 (3.9) 98.0 (4.0) 96.4 (2.8) 100.4 (3.2) 97.5 (3.5) 99.3 (3.7) 104.8 (4.1) 97.7 (2.6) 100 (2.0) 103.1 (2.7) 102.6 (4.1) 102.2 (2.5) 96.5 (2.7)
a
Means of triplicate analysis (%R.S.D.).
In a complementary experiment, the effect of volume of 0.5 M nitric acid in the quantitative stripping of Be from the 2% Q-MMP was investigated. The stripping was conducted using 1.0, 2.0, 2.5, 3.0, 4.0 and 5.0 mL portions of nitric acid. A 2.5 mL solution of nitric acid 0.5 M was sufficient for the full stripping off the Be. However, to ensure complete recovery, stripping was carried out using 3.0 mL 0.5 M nitric acid solutions. 3.7. Stability of the modified microparticles in experimental conditions Stability of the 2% Q-MMP under experimental conditions was examined by using 5.0 mg of 2% Q-MMP in several extraction/stripping conditions. After four cycles of extraction and back-extraction, some darkness appeared in the solution surface that could not be removed from the solution even by centrifugation (due to the use of sonication). Therefore, the stability of the 2% Q-MMP is limited to only 4 cycles of extraction/back-extraction. 3.8. Selectivity of the extraction Selective separation and determination of Be from its binary mixtures with diverse metal ions were investigated by using 2% Q-MMP and the aqueous solutions containing 200.0 ng of Be in the presence of mg levels of interfering ions and complexing agents (Table 2). According to the results, the recovery of Be at ng level was also quantitative in the presence of mg levels of the interfering diverse ions as their chloride, nitrate, sulfate and perchlorate salts. The selectivity of the current method is much higher than that of the solid phase extraction, which was reported by Yamini et al. [20]. In the current study, there was no need to use a masking agent (thiourea) to separate Fe3+ from Be (as Be2+ ). The amounts of the interfering ions for Mg2+ and Ca2+ were 40 and 32 times, respectively, higher than those reported by Yamini et al. [20]. Although in their study the separation efficiency was dropped to 39% [20] in the
presence of EDTA when using solid phase extraction for the recovery of Be, no such effect was found in our study when using EDTA at 270 times higher concentration than that of their study. Also, the selectivity of the current method is compared against the standardized portable fluorescence method reported, where potentially interfering metals were used at ≥400-fold molar excess to beryllium (Agrawal et al. [21,22]). By converting the molar ratio to mg and comparing the reported selectivity values, it can be concluded that the amounts of the interfering ions used in our study for Li, Co, Fe, Zn and Ni, are respectively 30.0, 4.0, 3.0, 2.5 and 1.5 times, higher than those of their study. However, the selectivity for Ca, Pb and Cu in this study are respectively decreased to 0.9, 0.4 and 0.1 of those report. 3.9. The analytical performance of the new method for the analysis of real samples For assessing the capability of the method for the recovery of Be from real samples containing varying amounts of diverse ions, two different real samples (tap water and spring water) were chosen and the method was applied for the preconcentration, separation and quantification of spiked Be (200.0 ng in 100.0 mL water samples). Fifteen mg Q-MMP was used. The water samples were collected from Hunan University area located on the west of Changsha City (Yuelu Shan) in the Hunan Province of the Peoples Republic of China. Table 3 shows the complementary characteristics and recovery percent of spiked Be. Results show that Be recovery was almost quantitative. Detection limit (LOD) of the current method under optimal experimental conditions was obtained at 30.0 ng L−1 , which is better than those obtained by solid phase extraction–flame atomic absorption, 200 ng L−1 [20] and 300 ng L−1 [38], chelation ion chromatography 35 g L−1 [39], adsorptive stripping voltammetry 30 ng L−1 [40], although, the detection limit of the method is less than the expensive and instrumental preconcentration and determination method such as extraction and GF-AAS 0.6 ng L−1 [4], 2.3 ng L−1 [16] and fluorometric determination 20 ng L−1 [41]. 3.10. Certified reference material analysis For approving the capability of the studied method, a mixture of two aqueous environmental Certified Reference Materials (GSBZ 50009-88 and GSB 07-1178-2000) from National Certified Reference Materials (P.R. China) was prepared and analyzed by the introduced method. The prepared sample contained 20.0 g L−1 Be along with Cu, Pb, Zn, Cd, Ni, Cr, K, Na, Ca, Mg at 1.13, 1.56, 0.390, 0.129, 0.648, 0.791, 4.60, 10.0, 20.0, 5.1 mg L−1 levels, respectively. The obtained recovery percent for Be was 99.96 ± 5.22% (n = 5). Therefore, the accuracy and the precision of the introduced method obtained in this study are in good agreement with the reference data. 4. Conclusions The introduced method for the recovery of Be based on Q-MMP as extractant shows good capability for the selective and quantitative separation and preconcentration of Be from the aqueous samples without any filtration step. Also, the applied photometric
Table 3 Characterization and recovery of the spiked Be on the different water samples used at optimum experimental conditions [100.0 mL of spring and tap water containing 200.0 ng Be, at pH 7.4 contacted with 15.0 mg of 2% quinalizarine-modified magnetic microparticles (Q-MMP) at the optimum experimental conditions]. Sample
pH
Conductivity (S cm−1 )
Ca (ppm)
K (ppm)
Mg (ppm)
Na (ppm)
Recoverya (%w/w)
Spring water Tap water
6.32 6.48
78.6 221
7.50 35.8
0.97 2.27
3.97 3.92
0.56 3.65
94.8 (1.7) 97.1 (1.6)
a
Means of triplicate analysis (%R.S.D.).
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procedure showed good precision in comparison to other instrumental analytical methods such as flame and electrothermal atomic absorption, ion chromatography and stripping voltammetry. The results also showed that the selectivity of the extraction relies on the modification of magnetic microparticles with quinalizarine. Such principle was developed by the ANL as an environmentally friendly method for treatment and remediation of waste [25]. Then the introduced principles were applied for the selective separation of metal ions, radionuclides and organic compounds [24–30]. This method was also applied by the current authors for the selective and quantitative separation of copper [33]. Therefore, this method can potentially be applied as a fast and simple procedure for the recovery and analysis of metal ions specifically and other compounds in general. Significant decrease in the consumption level of chemical reagents (solvent and extractant) is another advantage, which renders this as an environmentally friendly method for the fast preconcentration and separation purposes. Acknowledgments This work was supported in part by the National Key Basic Research Program of China (2002CB513110), Key Technologies Research and Development Program (2003BA310A16), Key Project of Natural Science Foundation of China (90606003), Natural Science Foundation of China (20475015), and China National Key Projects (2005EP090026). The authors would also like to appreciate the NSTRI (Nuclear Science and Technology Research Institute) and Ministry of Science, Research and Technology of Iran for the scholarship and financial support. Also special thanks go to Dr. K. Rezaei from the University of Tehran for editing the manuscript. References [1] M.B. Robert, O. Mark, Beryllium and Beryllium Compounds. Concise International Chemical Assessment Document 32, World Health Organization, Geneva, 2001, pp. 1–11. [2] Reference library at web site: www.espi-metals.com/metals (2009-01-27). [3] D.R. McAlister, E.P. Horwitz, Talanta 67 (2005) 873. [4] T. Okutani, Y. Tsuruta, A. Sakuragawa, Anal. Chem. 65 (1993) 1273. [5] A.E. Greenberg, L.S. Clesceri, A.D. Eaton, APHA, Standard Methods for the Examination of Water and Wastewater, 18th ed., Washington, DC, 1992, pp. 3–53. [6] Toxicological Review of Beryllium and Compounds (CAS No.7440-41-7), U.S. Environmental Protection Agency (EPA/635/R-98/008), Washington, DC, 1998.
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