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Hydride generation atomic absorption spectrometric determination of bismuth after separation and preconcentration with modified alumina
Farid Shakerian1,2, Ali Mohammad Haji Shabani1, Shayessteh Dadfarnia1,*, Mahboubeh Kazemi Avanji1 1
Department of Chemistry, Faculty of Science, Yazd University, Yazd, 89195-741, Iran
2
Present address: Department of Chemistry, Seoul National University, Seoul 151-747, Korea
Running title: Hydride generation atomic absorption spectrometric determination of bismuth
Correspondence: Shayessteh dadfarnia, Department of Chemistry, Faculty of Science, Yazd University, Yazd, 89195-741, Iran E-mail: [email protected] Fax: +98-35-38210644
Keywords: Bismuth / Hydride generation / Modified alumina / Solid-phase extraction
Received: 22-Sep-2014; Revised: 03-Dec-2014; Accepted: 08-Dec-2014 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/jssc.201401050. This article is protected by copyright. All rights reserved.
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Abstract A simple and sensitive method has been developed for the trace determination of bismuth in aqueous samples by a combination of solid-phase extraction and hydride generation atomic absorption spectrometry. The method is based on the use of a column packed with 2mercaptobenzothiazole immobilized on sodium dodecyl sulfate coated alumina. Different parameters influencing the separation and preconcentration of bismuth such as pH, sample volume, type and concentration of eluent, and the flow rate of sample and eluent were studied. A sample volume of 500.0 mL resulted in a preconcentration factor of 100. The precision (relative standard deviation, N = 10) at the 300 ng L−1 level and the limit of detection (3s) were found to be 2.3% and 12 ng L−1, respectively. The developed method was successfully applied to the determination of bismuth in natural water samples and two certified reference materials.
1 Introduction Bismuth and its compounds are used in semiconductors, medicines (for the treatment of syphilis, peptic ulcers, dermatological disorders, diarrhea, gastric and duodenal ulcer diseases), cosmetic preparations (such as pigments in eye shadow, creams, hair dyes, and lipsticks), alloys, and is present as byproduct of copper and tin refining, metallurgical additives, and the preparation and recycling of uranium nuclear fuels [1,2]. Bismuth is moderately toxic to human beings, plants, and animals. There are some reports that the digestion of bismuth and its compounds may result in kidney damage, gingivitis, rheumatic pain, fever and problems in hepatic function [3,4]. The concentration of bismuth in sea water -1
-1
is about 20 ng L , whereas its concentration in fresh water is very low, typically 200 ng L
[5,6]. Therefore, the determination of bismuth at trace levels in biological, environmental, and water samples is very important.
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There are many methods for the determination of bismuth in various matrices such as flame atomic absorption spectrometry [7,8] graphite furnace atomic absorption spectrometry (GFAAS) [9], atomic fluorescence spectrometry (AFS) [10], inductively coupled plasma mass spectrometry (ICP-MS) [11], spectrophotometry [12,13] and adsorptive anodic stripping voltammetry [14]. Some of these techniques such as GFAAS and ICP-MS usually have enough sensitivity for the determination of this element at trace level, but suffer from matrix interferences and ICP-MS is expensive and is not available in many laboratories due to its high cost. Compared with other techniques, FAAS has the advantages of simplicity, low cost, good selectivity and high sample throughput [15]. However, due to the relatively poor sensitivity, direct determination of trace amounts of bismuth in water samples by this technique is seldom carried out. Hydride generation combined with AAS has become a well-established technique for the determination of elements like bismuth, arsenic, selenium, antimony, lead, tellurium and germanium either directly or after a suitable pretreatment step. The generation of volatile hydrides enables an efficient matrix removal and an excellent analyte introduction to AAS. The advantages of the hydride generation atomic absorption spectrometry (HGAAS) are separation of analyte from the sample matrix, high efficiency of sample introduction, good sensitivity, ease of automation, and possibility of chemical speciation [16]. The sensitivity and detection limit for the analyte determination can be significantly improved by the combination of a separation/preconcentration method with the instrumental technique of analysis. Various separation and preconcentration methods such as LLE [17,18], ion exchange [19], cloud point extraction (CPE) [6,20,21], dispersive liquid–liquid microextraction [22] and SPE [13,23–27] have been proposed for the separation and preconcentration of bismuth. Among these methods, SPE in combination with HGAAS has
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become increasingly popular because it reduces the interferences effects (especially those caused by transition metal ions and volatile hydride forming elements) and simple operation. 2-Mercaptobenzothazole (MBT), with sulfur and nitrogen donor atoms, as a chelating agent has been immobilized on different supports and used for the separation and preconcentration of some metal ions including bismuth [28–32]. It has also been used in the construction of ion-selective electrodes [33,34]. In this study, MBT immobilized on surfactant-coated alumina is used for the separation and preconcentration of Bi(III) ions from aqueous solutions. The separated and preconcentrated bismuth is then determined with HGAAS.
2 Materials and methods
2.1 Apparatus An atomic absorption spectrometer (Analytik Jena, model 330, Germany) was used for the determination of bismuth. A bismuth hollow cathode lamp was used as the light source. The lamp current adjusted to 4 mA as recommended by the manufacture. The wavelength and slit width were 223.1 and 0.2 nm, respectively. A hydride generation system Analytik Jena novAA 300 (model HG-60) was used to produce the volatile hydride. NaBH4 was used as the chemical reagent in the hydride generation. Argon gas was used as the carrier gas, and the atomizer was an electrical heated quartz tube. The reagents concentrations, the reaction time and the argon gas flow rate were optimized considering the higher signal intensity. All the measurements were carried out under the optimized conditions given in Table 1. A Metrohm pH meter (model 691, Switzerland) was used for pH measurements with a combined glass electrode.
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2.2 Reagents All chemicals were of the highest purity available from Merck (Darmstadt, Germany) and were used without further purification. Distilled deionized water was used throughout the experiments. All glassware were soaked in 10% v/v nitric acid solution for at least 24 h and then thoroughly washed with distilled water before use. A stock solution of 1000 μg L-1 bismuth was prepared by dissolving appropriate amount of Bi(NO3).5H2O in 4.0 mL concentrated nitric acid and diluted to 100 mL with deionized water. Working solutions were prepared daily from the stock solution by serial dilution with distilled water. γ-Alumina particles (10–50 µm, chromatographic grade) were purified by shaking with 5.0 mol L-1 nitric acid and washing with distilled water three times. An ammoniacal MBT-SDS solution was prepared by dissolving 1 g of SDS and 140 mg of MBT in 50 mL of 0.1 mol L-1 aqueous ammonia and diluting to 100 mL with distilled water. A 2% m/v sodium tetrahydroborate (NaBH4) solution was prepared fresh daily by dissolving the solid reagent in 0.7% m/v sodium hydroxide solution.
2.3 Preparation of sorbent Ten milliliter of ammoniacal MBT-SDS solution was added to 1.5 g of the alumina and 40.0 mL of distilled water. The suspension was acidified to pH ~ 2.0 by addition of diluted hydrochloric acid solution and was stirred with a magnetic stirrer for 15 min. The solid material was then filtered through a sintered glass funnel using a vacuum pump, washed with distilled water, air-dried, and was kept in a closed brown bottle before use. This adsorbent was stable for more than two months.
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2.4 Procedure A small amount of glass wool was placed in the end of the glass column to prevent the loss of the adsorbent and was packed with 300 mg of the MBT immobilized on SDS coated alumina (7 mm height and 5 mm internal diameter). The pH of the sample solution was adjusted to ~ 2.0 by hydrochloric acid solution, and then the sample solution was passed through the column at a flow rate of 6.0 mL min-1 with the aid of a suction pump. The retained analyte was eluted from the sorbent with 5.0 mL of solution containing thiourea (0.2 mol L-1) and hydrochloric acid (2.0 mol L-1) with a flow rate of 3.0 mL min-1. The eluent was then transferred to the reduction cell. 5 mL of 2% w/v of NaBH4 solution was added through the peristaltic pump (Figure 1). The produced hydride was then directed to the electrically heated quartz tube (960°C) by a stream of argon at 160 mL min-1 and the amount of bismuth was determined by atomic absorption spectrometry. All measurements were evaluated as integrated absorbance (peak area).
3 Results and discussion Activated alumina can function as either cation or anion exchanger depending on the solution pH. When the pH is below its point of zero charge (PZC) (pH 8.5), the alumina surface is positively charged and can strongly adsorb anionic surfactants such as SDS through the negatively charged sulfate group. This results in the formation of aggregates termed hemimicelles and ad-micelles [35]. MBT is insoluble in water, but is soluble in alkaline aqueous solution and common organic solvents including ethanol, acetone and benzene. In preliminary experiments it was observed that the hydrophilic alumina surface has no adsorption affinity for MBT ligand. However, when the γ-alumina was mixed with the acidified solution of SDS and MBT, the ligand was homogeneously trapped on the hemimicelles or admicelles formed by SDS on alumina surface similar to that reported for
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other hydrophobic ligands [36–39] and the color of alumina was changed from white to pale yellow. The immobilization of MBT on the surfactant coated alumina was further confirmed by FTIR spectroscopy. The characteristic IR bands of immobilized MBT on alumina were 2855.2 (S–H stretching), 1384.9 (C=N stretching), and 1468.9 cm-1 (C=C stretching band of aromatic ring). The bands of 1256.5 (S=O stretching) and 2925.1 cm-1 (C–H stretching of aliphatic chain) related to surfactant were also observed in FTIR spectrum [S1]. The optimization of the SPE method was accomplished by the univariant method (keeping all variable constant except one). The influence of pH, sample volume, type and concentration of eluent, and the sample and eluent flow rates was investigated to obtain the best conditions. pH is an important parameter affecting the adsorption of cations from aqueous samples. To understand the uptake behavior of sorbent as a function of pH, the effect of the sample pH on the sorption of bismuth was studied by varying the pH within the range of 0.5–8.0 [S2]. The results indicated that the recovery of bismuth was maximized in the pH range of 2.0–6.0. The decrease in the recovery at pH less than 2.0 is probably due to the protonation of ligand, whereas the decrease of recovery at pH higher than 6.0 may be due to the hydrolysis of Bi(III). Thus, to have good selectivity, the pH of 2.0 was selected for the subsequent works. Desorption of the analyte from the sorbent is an important step in SPE studies. The eluent should completely elute the analyte content of the column in a minimum volume of solvent and should not interfere in its measurement. The study of the effect of pH on the sorption indicates that the adsorption of bismuth at pH < 1.0 is negligible. Therefore, one can expect that the elution may be favored in acidic solution. For this purpose, the retained bismuth on the column (0.125 µg) was eluted with 5.0 mL of various eluents including; nitric
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acid, hydrochloric acid, and acidified thiourea solutions [S3]. The results showed that 5.0 mL of solution containing thiourea (0.2 mol L-1) and hydrochloric acid (2 mol L-1) is the best eluent for quantitatively striping of the retained bismuth ions from the packed column. It is known that the extraction efficiency of the analyte by the adsorbent depends on the sample flow rate. The flow rate should enable the achievement of equilibrium between the analyte and the adsorbent. The effect of the sample flow rate in the range of 2.0–10.0 mL min-1, on the recovery of 0.125 µg of bismuth from 300 mL of solution was examined [S4]. The results showed that the kinetic of adsorption was relatively fast and up to the flow rate of 6.0 mL min-1 the retention of bismuth was independent of the flow rate. Therefore, a sample flow rate of 6 mL min-1 was selected. Next, the influence of eluent flow rate on the analyte desorption from the column was studied by varying the flow rate between 0.5–7.0 mL min-1. The results showed that the kinetic of analyte desorption was slower and the quantitative recovery of the bismuth was possible up to a flow rate of 3.0 mL min-1. Therefore, a flow rate of 3.0 mL min-1was selected for the subsequent studies. The amount of adsorbent has a critical role on the quantitative recovery of analyte from the sample solution. The quantitative retention of analyte is not possible with low amount of sorbent, but the excess amount of sorbent may reduce the flow rate of the sample through the column and it also may prevent quantitative elution of analyte by a small volume of eluent. Therefore, the influence of the amount (50–500 mg) of MBT immobilized on SDS-coated alumina on the recovery of the bismuth ions from the solution was examined. The results showed that the quantitative recovery (> 95%) of the analyte is possible when the adsorbent amount is greater than 250 mg. So, 300 mg of the adsorbent was selected for the further studies.
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To explore the possibility of enrichment of trace amounts of bismuth from the large sample volumes, the influence of sample volume on the recovery of analyte was also investigated. Different sample volumes (50–800 mL) containing 0.125 µg of bismuth were passed through the column. The results showed that quantitative recoveries (> 95%) were obtained up to 500 mL of the sample solution [S5]. Thus, the method has the ability of achieving high preconcentration factor (100) for bismuth ions.
3.1 Interferences study The influence of potentially interfering ions on the recovery of 0.125 µg Bi(III) from 300 mL of sample solution was investigated under the optimized conditions. Table 2 shows the tolerance limits with an experimental error of less than 5%. The results revealed that the effect of various ions on the recovery and measurement of the analyte are negligible and Bi(III) can be determined quantitatively in the presence of foreign ions at the given mole ratio. Thus, the method has high selectivity for bismuth ions.
3.2 Analytical performance For a sample volume of 300 mL, the calibration curve showed good linearity with a correlation coefficient of 0.9995 within the concentration range of 40–1250 ng L−1 of Bi(III). The enhancement factor calculated as the ratio of the slopes of the calibration graphs with and without preconcentration was found to be 58.4 for 300 mL sample volume. The LOD based on the three times the SD of blank signal was found to be 12 ng L−1 for a sampling volume of 300 mL. The RSD (N = 10) at 300 ng L−1 of bismuth was 2.3%. The maximum capacity of the sorbent was determined by batch method i.e. to 0.5 g of 2-mercaptobenzothiazole immobilized on SDS coated alumina, 100 mL of solution
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containing 3 mg of Bi(III) at pH = 2 was added. After shaking for 30 min, the mixture was filtered through a sintered glass funnel and the amount of bismuth left in filtrate was determined by flame atomic absorption spectrometry. The capacity of the sorbent was found to be 2.7 mg of bismuth per gram of the sorbent.
3.3 Applications The proposed method was applied to the determination of bismuth in fresh water including; tap water, river water, and well water samples. The results are listed in Table 3. The accuracy of the method was verified by the recovery experiments. Good recoveries of the spiked samples (95.0–103.0%) indicate the successful applicability of the proposed method for the determination of bismuth in water samples. The method was also validated by analyzing two certified reference materials of lead concentrate (CPB-1, Canadian Certified Reference Materials Project) and trace elements in lead (BCR No 288, Community Bureau of Reference-BCR, Brussels). The concentration of bismuth was found to be 227 ± 15 and 211 ± 12 µg g-1 for CPB-1 and BCR No 288, respectively. At 95% confidence level, this is a good agreement with the accepted values of 230 ± 20 µg g-1 for CPB-1 and 215.8 ± 2.4 µg g-1 for BCR No 288.
3.4 Comparison with other SPE methods The proposed method was compared with the other reported methods for the SPE and determination of bismuth. The results are given in Table 4. These results indicate that the proposed method provides a lower LOD and the preconcentration factor is higher than most of the others [7,9,23,25–27]. Furthermore, the separation of bismuth from the sample matrices causes sample cleanup through the elimination of the interferences in the hydride generation step, which increased the measurement sensitivity.
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4 Conclusion SPE combined with HGAAS is a simple, sensitive and accurate way for the determination the ultra-trace amounts of bismuth in aqueous solution. A high enhancement factor (58.4) and low detection limit (12 ng L−1) were achieved with only 300.0 mL of sample. The sensitivity of method can be enhanced by increasing the sample volume up to 500 mL but the analysis time would also increase. The preparation of adsorbent is easy and does not require any chemical reactions. The proposed method is perfectly applicable for the determination of bismuth in fresh water samples.
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118–125. [12] Burns, D. T., Tungkananuruk, N., Thuwasin, S., Anal. Chim. Acta 2000, 419, 41–44. [13] Madrakian, T., Afkhami, A., Esmaeili, A., Talanta 2003, 60, 831–838. [14] Guo, H., Li, Y., Xiao, P., He, N., Anal. Chim. Acta 2005, 534, 143–147. [15] Pereira, M. G., Arruda, M. A. Z., Microchim. Acta 2003, 141, 115–131. [16] Zhang, Y., Adeloju, S. B., Talanta 2008, 76, 724–730. [17] Yang, J.-G., Yang, J.-Y., Tang, M.-T, Tang, C.-B., Liu, W., Hydrometallurgy 2009, 96, 342–348. [18] Alonso, A., Almendral, M.J., Baez, M.D., Porras, M.J., Lopez Lavin, F., Garcia de Maria, C., Anal. Chim. Acta 2000, 408, 129–133. [19] Mandal, B., Ghosh, N., J. Hazard. Mater. 2010, 182, 363–370. [20] Afkhami, A., Madrakian, T., Siampour, H., J. Braz. Chem. Soc. 2006, 17, 797–802. [21] Sun, M., Wu, Q., J. Hazard. Mater. 2011, 192, 935–939. [22] Jia, X., Han, Y., Liu, X., Duan, T., Chen, H., Microchim. Acta 2010, 171, 49–56. [23] Tokman, N., Akman, S., Anal. Chim. Acta 2004, 519, 87–91. [24] Taher, M. A., Rezaeipour, E., Afzali, D., Talanta 2004, 63, 797–801. [25] Pournaghi-Azar, M., Djozan, D., Anal. Chim. Acta 2001, 437, 217–224. [26] Tokman, N., Akman, S., Ozcan, M., Talanta 2003, 59, 201–205. [27] Moyano, S., Wuilloud, R., Olsina, R., Gásquez, J., Martinez, L., Talanta 2001, 54, 211– 219. [28] Safavi, A., Iranpoor, N., Saghir, N., Sep. Purif. Technol. 2004, 40, 303–308. [29] Terada, K., Matsumoto, K., Inaba, T., Anal. Chim. Acta 1985, 170, 225–235. [30] Absalan, G., Mehrdjardi, M. A., Sep. Purif. Technol. 2003, 33, 95–101. [31] Mladenova, E., Karadjova, I., Tsalev, D. L., J. Sep. Sci. 2012, 35, 1249–1265. [32 ] Ishida, K., Puri, B. K., Satake, M., Talanta 1985, 32, 207–208.
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[33] Shervedani, R. K., Babadi, M. K., Talanta 2006, 69, 741–746. [34] Shokrollahi, A., Ghaedi, M., Montazerozohori, M., Hosaini, O., Ghaedi, H., Anal. Lett. 2007, 40, 1714–1735. [35] Moradi, M., Yamini, Y., J. Sep. Sci. 2012, 35, 2319–2340. [36] Hiraide, M., Iwasawa, J., Hiramatsu, S., Kawaguchi, H., Anal. Sci. 1995, 11, 611–615. [37] Manzoori, J.L, Sorouraddin, M.H., Haji Shabani, A.M., J. Anal. At. Spectrom. 1998, 13, 305–308. [38] Haji Shabani, A. M., Dadfarnia, S., Dehghani, Z., Talanta 2009, 79, 1066–1070. [39] Ghaedi, M., Tavallali, H., Shokrollahi, A., Zahedi, M., Montazerozohori, M., Soylak, M., J. Hazard. Mater. 2009, 166, 1441–1448.
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Figure 1. Schematic diagram of the HGAAS apparatus.
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Table 1. Analytical parameters of the HGAAS system for the determination of bismuth
Parameter
Condition
Determination mode
Batch
Integration time (s)
50 -1
Argon flow rate (mL min )
160
Cell temperature (ºC)
960
Sample volume (mL)
5
NaBH4 concentration (w/v%)
2
NaBH4 flow rate (mL min-1)
15
NaBH4 pumping time (S)
20
Wavelength (nm)
223.1
Bandwidth (nm)
0.2
Lamp current (mA)
4.0
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Table 2. Effect of the interfering ions on the recovery of 0.25 µg bismuth from 300 mL of sample solution
Mole ratio (Ion/Bi3+)
Recovery (%)
Ca2+
10000
95.2
-
Interfering ion
Cl
10000
98.6
Co
2+
10000
95.7
Cr3+
10000
95.2
Fe3+
10000
96.7
K+
10000
96.0
Mg2+
10000
96.8
2+
Mn
10000
97.4
Na+
10000
103.4
NO3-
10000
102.4
Pb2+
10000
96.0
Sb3+
10000
104.5
Se4+
10000
98.5
Zn
2+
10000
98.0
Cd2+
5000
95.3
Hg2+
5000
103.5
Ni2+
5000
95.2
SO42-
5000
100.3
ClO4-
2000
96.8
Ag
1000
97.7
Cu2+
1000
102.1
Sn2+
250
95.9
+
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Table 3. Determination of bismuth in natural water samples. Sample volume 300 Ml
Water sample
Bismuth added (ng L-1) Bismuth found (ng L-1)*
Recovery (%)
Tap water
River water 1
River water 2
Well water
*
-
156 3
-
100
251 8
95.0
300
452 13
98.7
-
72 2
-
100
170 4
98.0
300
364 11
97.3
-
53 ± 1
-
100
156 ± 5
103.0
300
351 ± 15
99.3
-
450 17
-
100
545 21
95.0
300
744 21
98.0
Average and standard deviation of three analyses.
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Table 4. Comparison of the proposed method with some reported solid phase extraction for Bi(III)
Adsorbent
Reagent
LOD
PF -1
Linear range -1
(ng L )
Capacity
Analytical technique
Ref.
-1
(ng L )
(mg g )
Lewatit TP-207
-
2750
20
-
2.6
FAAS
[7]
Octadecyl bonded silica cartridge
Cyanex 301
10
20
500-10000
-
GFAAS
[9]
Chromosorb-107
APDC
800
10
-
-
GFAAS
[23]
Amberlite XAD-2
5-Br-PADAP
140
110
50000-160000000
0.2
ASV-DPP
[24]
Octylsilane (RP-8) cartridge
Oxine
90
20
10000-1045000
-
ASV
[25]
Silica gel
3-aminopropyltriethoxysilane
500
5
-
6.7
GFAAS
[26]
Amberlite XAD-7
Quinolin-8-ol
20
10
-
5.2
HG-ICP-AES
[27]
Activated carbon
Thiourea-Bromide
170
250
200-31300
104.5
Spectrophotometry
[13]
Alumina
MBT
12
100
40 -1250
2.7
HGAAS
This work
LOD: limit of detection, PF: preconcentration factor, APDC: Ammonium pyrolidinedithiocarbamate, 5-Br-PADAP: 2-(5-Bromo-2-pyridylazo)-5-diethyl aminophenol.
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Hydride generation atomic absorption spectrometric determination of bismuth after separation and preconcentration with modified alumina
Farid Shakerian1,2, Ali Mohammad Haji Shabani1, Shayessteh Dadfarnia1,*, Mahboubeh Kazemi Avanji1 1
Department of Chemistry, Faculty of Science, Yazd University, Yazd, 89195-741, Iran
2
Present address: Department of Chemistry, Seoul National University, Seoul 151-747, Korea
Running title: Hydride generation atomic absorption spectrometric determination of bismuth
Correspondence: Shayessteh dadfarnia, Department of Chemistry, Faculty of Science, Yazd University, Yazd, 89195-741, Iran E-mail: [email protected] Fax: +98-35-38210644
Keywords: Bismuth / Hydride generation / Modified alumina / Solid-phase extraction
Received: 22-Sep-2014; Revised: 03-Dec-2014; Accepted: 08-Dec-2014 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/jssc.201401050. This article is protected by copyright. All rights reserved.
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Abstract A simple and sensitive method has been developed for the trace determination of bismuth in aqueous samples by a combination of solid-phase extraction and hydride generation atomic absorption spectrometry. The method is based on the use of a column packed with 2mercaptobenzothiazole immobilized on sodium dodecyl sulfate coated alumina. Different parameters influencing the separation and preconcentration of bismuth such as pH, sample volume, type and concentration of eluent, and the flow rate of sample and eluent were studied. A sample volume of 500.0 mL resulted in a preconcentration factor of 100. The precision (relative standard deviation, N = 10) at the 300 ng L−1 level and the limit of detection (3s) were found to be 2.3% and 12 ng L−1, respectively. The developed method was successfully applied to the determination of bismuth in natural water samples and two certified reference materials.
1 Introduction Bismuth and its compounds are used in semiconductors, medicines (for the treatment of syphilis, peptic ulcers, dermatological disorders, diarrhea, gastric and duodenal ulcer diseases), cosmetic preparations (such as pigments in eye shadow, creams, hair dyes, and lipsticks), alloys, and is present as byproduct of copper and tin refining, metallurgical additives, and the preparation and recycling of uranium nuclear fuels [1,2]. Bismuth is moderately toxic to human beings, plants, and animals. There are some reports that the digestion of bismuth and its compounds may result in kidney damage, gingivitis, rheumatic pain, fever and problems in hepatic function [3,4]. The concentration of bismuth in sea water -1
-1
is about 20 ng L , whereas its concentration in fresh water is very low, typically 200 ng L
[5,6]. Therefore, the determination of bismuth at trace levels in biological, environmental, and water samples is very important.
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There are many methods for the determination of bismuth in various matrices such as flame atomic absorption spectrometry [7,8] graphite furnace atomic absorption spectrometry (GFAAS) [9], atomic fluorescence spectrometry (AFS) [10], inductively coupled plasma mass spectrometry (ICP-MS) [11], spectrophotometry [12,13] and adsorptive anodic stripping voltammetry [14]. Some of these techniques such as GFAAS and ICP-MS usually have enough sensitivity for the determination of this element at trace level, but suffer from matrix interferences and ICP-MS is expensive and is not available in many laboratories due to its high cost. Compared with other techniques, FAAS has the advantages of simplicity, low cost, good selectivity and high sample throughput [15]. However, due to the relatively poor sensitivity, direct determination of trace amounts of bismuth in water samples by this technique is seldom carried out. Hydride generation combined with AAS has become a well-established technique for the determination of elements like bismuth, arsenic, selenium, antimony, lead, tellurium and germanium either directly or after a suitable pretreatment step. The generation of volatile hydrides enables an efficient matrix removal and an excellent analyte introduction to AAS. The advantages of the hydride generation atomic absorption spectrometry (HGAAS) are separation of analyte from the sample matrix, high efficiency of sample introduction, good sensitivity, ease of automation, and possibility of chemical speciation [16]. The sensitivity and detection limit for the analyte determination can be significantly improved by the combination of a separation/preconcentration method with the instrumental technique of analysis. Various separation and preconcentration methods such as LLE [17,18], ion exchange [19], cloud point extraction (CPE) [6,20,21], dispersive liquid–liquid microextraction [22] and SPE [13,23–27] have been proposed for the separation and preconcentration of bismuth. Among these methods, SPE in combination with HGAAS has
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become increasingly popular because it reduces the interferences effects (especially those caused by transition metal ions and volatile hydride forming elements) and simple operation. 2-Mercaptobenzothazole (MBT), with sulfur and nitrogen donor atoms, as a chelating agent has been immobilized on different supports and used for the separation and preconcentration of some metal ions including bismuth [28–32]. It has also been used in the construction of ion-selective electrodes [33,34]. In this study, MBT immobilized on surfactant-coated alumina is used for the separation and preconcentration of Bi(III) ions from aqueous solutions. The separated and preconcentrated bismuth is then determined with HGAAS.
2 Materials and methods
2.1 Apparatus An atomic absorption spectrometer (Analytik Jena, model 330, Germany) was used for the determination of bismuth. A bismuth hollow cathode lamp was used as the light source. The lamp current adjusted to 4 mA as recommended by the manufacture. The wavelength and slit width were 223.1 and 0.2 nm, respectively. A hydride generation system Analytik Jena novAA 300 (model HG-60) was used to produce the volatile hydride. NaBH4 was used as the chemical reagent in the hydride generation. Argon gas was used as the carrier gas, and the atomizer was an electrical heated quartz tube. The reagents concentrations, the reaction time and the argon gas flow rate were optimized considering the higher signal intensity. All the measurements were carried out under the optimized conditions given in Table 1. A Metrohm pH meter (model 691, Switzerland) was used for pH measurements with a combined glass electrode.
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2.2 Reagents All chemicals were of the highest purity available from Merck (Darmstadt, Germany) and were used without further purification. Distilled deionized water was used throughout the experiments. All glassware were soaked in 10% v/v nitric acid solution for at least 24 h and then thoroughly washed with distilled water before use. A stock solution of 1000 μg L-1 bismuth was prepared by dissolving appropriate amount of Bi(NO3).5H2O in 4.0 mL concentrated nitric acid and diluted to 100 mL with deionized water. Working solutions were prepared daily from the stock solution by serial dilution with distilled water. γ-Alumina particles (10–50 µm, chromatographic grade) were purified by shaking with 5.0 mol L-1 nitric acid and washing with distilled water three times. An ammoniacal MBT-SDS solution was prepared by dissolving 1 g of SDS and 140 mg of MBT in 50 mL of 0.1 mol L-1 aqueous ammonia and diluting to 100 mL with distilled water. A 2% m/v sodium tetrahydroborate (NaBH4) solution was prepared fresh daily by dissolving the solid reagent in 0.7% m/v sodium hydroxide solution.
2.3 Preparation of sorbent Ten milliliter of ammoniacal MBT-SDS solution was added to 1.5 g of the alumina and 40.0 mL of distilled water. The suspension was acidified to pH ~ 2.0 by addition of diluted hydrochloric acid solution and was stirred with a magnetic stirrer for 15 min. The solid material was then filtered through a sintered glass funnel using a vacuum pump, washed with distilled water, air-dried, and was kept in a closed brown bottle before use. This adsorbent was stable for more than two months.
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2.4 Procedure A small amount of glass wool was placed in the end of the glass column to prevent the loss of the adsorbent and was packed with 300 mg of the MBT immobilized on SDS coated alumina (7 mm height and 5 mm internal diameter). The pH of the sample solution was adjusted to ~ 2.0 by hydrochloric acid solution, and then the sample solution was passed through the column at a flow rate of 6.0 mL min-1 with the aid of a suction pump. The retained analyte was eluted from the sorbent with 5.0 mL of solution containing thiourea (0.2 mol L-1) and hydrochloric acid (2.0 mol L-1) with a flow rate of 3.0 mL min-1. The eluent was then transferred to the reduction cell. 5 mL of 2% w/v of NaBH4 solution was added through the peristaltic pump (Figure 1). The produced hydride was then directed to the electrically heated quartz tube (960°C) by a stream of argon at 160 mL min-1 and the amount of bismuth was determined by atomic absorption spectrometry. All measurements were evaluated as integrated absorbance (peak area).
3 Results and discussion Activated alumina can function as either cation or anion exchanger depending on the solution pH. When the pH is below its point of zero charge (PZC) (pH 8.5), the alumina surface is positively charged and can strongly adsorb anionic surfactants such as SDS through the negatively charged sulfate group. This results in the formation of aggregates termed hemimicelles and ad-micelles [35]. MBT is insoluble in water, but is soluble in alkaline aqueous solution and common organic solvents including ethanol, acetone and benzene. In preliminary experiments it was observed that the hydrophilic alumina surface has no adsorption affinity for MBT ligand. However, when the γ-alumina was mixed with the acidified solution of SDS and MBT, the ligand was homogeneously trapped on the hemimicelles or admicelles formed by SDS on alumina surface similar to that reported for
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other hydrophobic ligands [36–39] and the color of alumina was changed from white to pale yellow. The immobilization of MBT on the surfactant coated alumina was further confirmed by FTIR spectroscopy. The characteristic IR bands of immobilized MBT on alumina were 2855.2 (S–H stretching), 1384.9 (C=N stretching), and 1468.9 cm-1 (C=C stretching band of aromatic ring). The bands of 1256.5 (S=O stretching) and 2925.1 cm-1 (C–H stretching of aliphatic chain) related to surfactant were also observed in FTIR spectrum [S1]. The optimization of the SPE method was accomplished by the univariant method (keeping all variable constant except one). The influence of pH, sample volume, type and concentration of eluent, and the sample and eluent flow rates was investigated to obtain the best conditions. pH is an important parameter affecting the adsorption of cations from aqueous samples. To understand the uptake behavior of sorbent as a function of pH, the effect of the sample pH on the sorption of bismuth was studied by varying the pH within the range of 0.5–8.0 [S2]. The results indicated that the recovery of bismuth was maximized in the pH range of 2.0–6.0. The decrease in the recovery at pH less than 2.0 is probably due to the protonation of ligand, whereas the decrease of recovery at pH higher than 6.0 may be due to the hydrolysis of Bi(III). Thus, to have good selectivity, the pH of 2.0 was selected for the subsequent works. Desorption of the analyte from the sorbent is an important step in SPE studies. The eluent should completely elute the analyte content of the column in a minimum volume of solvent and should not interfere in its measurement. The study of the effect of pH on the sorption indicates that the adsorption of bismuth at pH < 1.0 is negligible. Therefore, one can expect that the elution may be favored in acidic solution. For this purpose, the retained bismuth on the column (0.125 µg) was eluted with 5.0 mL of various eluents including; nitric
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acid, hydrochloric acid, and acidified thiourea solutions [S3]. The results showed that 5.0 mL of solution containing thiourea (0.2 mol L-1) and hydrochloric acid (2 mol L-1) is the best eluent for quantitatively striping of the retained bismuth ions from the packed column. It is known that the extraction efficiency of the analyte by the adsorbent depends on the sample flow rate. The flow rate should enable the achievement of equilibrium between the analyte and the adsorbent. The effect of the sample flow rate in the range of 2.0–10.0 mL min-1, on the recovery of 0.125 µg of bismuth from 300 mL of solution was examined [S4]. The results showed that the kinetic of adsorption was relatively fast and up to the flow rate of 6.0 mL min-1 the retention of bismuth was independent of the flow rate. Therefore, a sample flow rate of 6 mL min-1 was selected. Next, the influence of eluent flow rate on the analyte desorption from the column was studied by varying the flow rate between 0.5–7.0 mL min-1. The results showed that the kinetic of analyte desorption was slower and the quantitative recovery of the bismuth was possible up to a flow rate of 3.0 mL min-1. Therefore, a flow rate of 3.0 mL min-1was selected for the subsequent studies. The amount of adsorbent has a critical role on the quantitative recovery of analyte from the sample solution. The quantitative retention of analyte is not possible with low amount of sorbent, but the excess amount of sorbent may reduce the flow rate of the sample through the column and it also may prevent quantitative elution of analyte by a small volume of eluent. Therefore, the influence of the amount (50–500 mg) of MBT immobilized on SDS-coated alumina on the recovery of the bismuth ions from the solution was examined. The results showed that the quantitative recovery (> 95%) of the analyte is possible when the adsorbent amount is greater than 250 mg. So, 300 mg of the adsorbent was selected for the further studies.
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To explore the possibility of enrichment of trace amounts of bismuth from the large sample volumes, the influence of sample volume on the recovery of analyte was also investigated. Different sample volumes (50–800 mL) containing 0.125 µg of bismuth were passed through the column. The results showed that quantitative recoveries (> 95%) were obtained up to 500 mL of the sample solution [S5]. Thus, the method has the ability of achieving high preconcentration factor (100) for bismuth ions.
3.1 Interferences study The influence of potentially interfering ions on the recovery of 0.125 µg Bi(III) from 300 mL of sample solution was investigated under the optimized conditions. Table 2 shows the tolerance limits with an experimental error of less than 5%. The results revealed that the effect of various ions on the recovery and measurement of the analyte are negligible and Bi(III) can be determined quantitatively in the presence of foreign ions at the given mole ratio. Thus, the method has high selectivity for bismuth ions.
3.2 Analytical performance For a sample volume of 300 mL, the calibration curve showed good linearity with a correlation coefficient of 0.9995 within the concentration range of 40–1250 ng L−1 of Bi(III). The enhancement factor calculated as the ratio of the slopes of the calibration graphs with and without preconcentration was found to be 58.4 for 300 mL sample volume. The LOD based on the three times the SD of blank signal was found to be 12 ng L−1 for a sampling volume of 300 mL. The RSD (N = 10) at 300 ng L−1 of bismuth was 2.3%. The maximum capacity of the sorbent was determined by batch method i.e. to 0.5 g of 2-mercaptobenzothiazole immobilized on SDS coated alumina, 100 mL of solution
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containing 3 mg of Bi(III) at pH = 2 was added. After shaking for 30 min, the mixture was filtered through a sintered glass funnel and the amount of bismuth left in filtrate was determined by flame atomic absorption spectrometry. The capacity of the sorbent was found to be 2.7 mg of bismuth per gram of the sorbent.
3.3 Applications The proposed method was applied to the determination of bismuth in fresh water including; tap water, river water, and well water samples. The results are listed in Table 3. The accuracy of the method was verified by the recovery experiments. Good recoveries of the spiked samples (95.0–103.0%) indicate the successful applicability of the proposed method for the determination of bismuth in water samples. The method was also validated by analyzing two certified reference materials of lead concentrate (CPB-1, Canadian Certified Reference Materials Project) and trace elements in lead (BCR No 288, Community Bureau of Reference-BCR, Brussels). The concentration of bismuth was found to be 227 ± 15 and 211 ± 12 µg g-1 for CPB-1 and BCR No 288, respectively. At 95% confidence level, this is a good agreement with the accepted values of 230 ± 20 µg g-1 for CPB-1 and 215.8 ± 2.4 µg g-1 for BCR No 288.
3.4 Comparison with other SPE methods The proposed method was compared with the other reported methods for the SPE and determination of bismuth. The results are given in Table 4. These results indicate that the proposed method provides a lower LOD and the preconcentration factor is higher than most of the others [7,9,23,25–27]. Furthermore, the separation of bismuth from the sample matrices causes sample cleanup through the elimination of the interferences in the hydride generation step, which increased the measurement sensitivity.
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4 Conclusion SPE combined with HGAAS is a simple, sensitive and accurate way for the determination the ultra-trace amounts of bismuth in aqueous solution. A high enhancement factor (58.4) and low detection limit (12 ng L−1) were achieved with only 300.0 mL of sample. The sensitivity of method can be enhanced by increasing the sample volume up to 500 mL but the analysis time would also increase. The preparation of adsorbent is easy and does not require any chemical reactions. The proposed method is perfectly applicable for the determination of bismuth in fresh water samples.
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118–125. [12] Burns, D. T., Tungkananuruk, N., Thuwasin, S., Anal. Chim. Acta 2000, 419, 41–44. [13] Madrakian, T., Afkhami, A., Esmaeili, A., Talanta 2003, 60, 831–838. [14] Guo, H., Li, Y., Xiao, P., He, N., Anal. Chim. Acta 2005, 534, 143–147. [15] Pereira, M. G., Arruda, M. A. Z., Microchim. Acta 2003, 141, 115–131. [16] Zhang, Y., Adeloju, S. B., Talanta 2008, 76, 724–730. [17] Yang, J.-G., Yang, J.-Y., Tang, M.-T, Tang, C.-B., Liu, W., Hydrometallurgy 2009, 96, 342–348. [18] Alonso, A., Almendral, M.J., Baez, M.D., Porras, M.J., Lopez Lavin, F., Garcia de Maria, C., Anal. Chim. Acta 2000, 408, 129–133. [19] Mandal, B., Ghosh, N., J. Hazard. Mater. 2010, 182, 363–370. [20] Afkhami, A., Madrakian, T., Siampour, H., J. Braz. Chem. Soc. 2006, 17, 797–802. [21] Sun, M., Wu, Q., J. Hazard. Mater. 2011, 192, 935–939. [22] Jia, X., Han, Y., Liu, X., Duan, T., Chen, H., Microchim. Acta 2010, 171, 49–56. [23] Tokman, N., Akman, S., Anal. Chim. Acta 2004, 519, 87–91. [24] Taher, M. A., Rezaeipour, E., Afzali, D., Talanta 2004, 63, 797–801. [25] Pournaghi-Azar, M., Djozan, D., Anal. Chim. Acta 2001, 437, 217–224. [26] Tokman, N., Akman, S., Ozcan, M., Talanta 2003, 59, 201–205. [27] Moyano, S., Wuilloud, R., Olsina, R., Gásquez, J., Martinez, L., Talanta 2001, 54, 211– 219. [28] Safavi, A., Iranpoor, N., Saghir, N., Sep. Purif. Technol. 2004, 40, 303–308. [29] Terada, K., Matsumoto, K., Inaba, T., Anal. Chim. Acta 1985, 170, 225–235. [30] Absalan, G., Mehrdjardi, M. A., Sep. Purif. Technol. 2003, 33, 95–101. [31] Mladenova, E., Karadjova, I., Tsalev, D. L., J. Sep. Sci. 2012, 35, 1249–1265. [32 ] Ishida, K., Puri, B. K., Satake, M., Talanta 1985, 32, 207–208.
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[33] Shervedani, R. K., Babadi, M. K., Talanta 2006, 69, 741–746. [34] Shokrollahi, A., Ghaedi, M., Montazerozohori, M., Hosaini, O., Ghaedi, H., Anal. Lett. 2007, 40, 1714–1735. [35] Moradi, M., Yamini, Y., J. Sep. Sci. 2012, 35, 2319–2340. [36] Hiraide, M., Iwasawa, J., Hiramatsu, S., Kawaguchi, H., Anal. Sci. 1995, 11, 611–615. [37] Manzoori, J.L, Sorouraddin, M.H., Haji Shabani, A.M., J. Anal. At. Spectrom. 1998, 13, 305–308. [38] Haji Shabani, A. M., Dadfarnia, S., Dehghani, Z., Talanta 2009, 79, 1066–1070. [39] Ghaedi, M., Tavallali, H., Shokrollahi, A., Zahedi, M., Montazerozohori, M., Soylak, M., J. Hazard. Mater. 2009, 166, 1441–1448.
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Figure 1. Schematic diagram of the HGAAS apparatus.
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Table 1. Analytical parameters of the HGAAS system for the determination of bismuth
Parameter
Condition
Determination mode
Batch
Integration time (s)
50 -1
Argon flow rate (mL min )
160
Cell temperature (ºC)
960
Sample volume (mL)
5
NaBH4 concentration (w/v%)
2
NaBH4 flow rate (mL min-1)
15
NaBH4 pumping time (S)
20
Wavelength (nm)
223.1
Bandwidth (nm)
0.2
Lamp current (mA)
4.0
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Table 2. Effect of the interfering ions on the recovery of 0.25 µg bismuth from 300 mL of sample solution
Mole ratio (Ion/Bi3+)
Recovery (%)
Ca2+
10000
95.2
-
Interfering ion
Cl
10000
98.6
Co
2+
10000
95.7
Cr3+
10000
95.2
Fe3+
10000
96.7
K+
10000
96.0
Mg2+
10000
96.8
2+
Mn
10000
97.4
Na+
10000
103.4
NO3-
10000
102.4
Pb2+
10000
96.0
Sb3+
10000
104.5
Se4+
10000
98.5
Zn
2+
10000
98.0
Cd2+
5000
95.3
Hg2+
5000
103.5
Ni2+
5000
95.2
SO42-
5000
100.3
ClO4-
2000
96.8
Ag
1000
97.7
Cu2+
1000
102.1
Sn2+
250
95.9
+
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Table 3. Determination of bismuth in natural water samples. Sample volume 300 Ml
Water sample
Bismuth added (ng L-1) Bismuth found (ng L-1)*
Recovery (%)
Tap water
River water 1
River water 2
Well water
*
-
156 3
-
100
251 8
95.0
300
452 13
98.7
-
72 2
-
100
170 4
98.0
300
364 11
97.3
-
53 ± 1
-
100
156 ± 5
103.0
300
351 ± 15
99.3
-
450 17
-
100
545 21
95.0
300
744 21
98.0
Average and standard deviation of three analyses.
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Table 4. Comparison of the proposed method with some reported solid phase extraction for Bi(III)
Adsorbent
Reagent
LOD
PF -1
Linear range -1
(ng L )
Capacity
Analytical technique
Ref.
-1
(ng L )
(mg g )
Lewatit TP-207
-
2750
20
-
2.6
FAAS
[7]
Octadecyl bonded silica cartridge
Cyanex 301
10
20
500-10000
-
GFAAS
[9]
Chromosorb-107
APDC
800
10
-
-
GFAAS
[23]
Amberlite XAD-2
5-Br-PADAP
140
110
50000-160000000
0.2
ASV-DPP
[24]
Octylsilane (RP-8) cartridge
Oxine
90
20
10000-1045000
-
ASV
[25]
Silica gel
3-aminopropyltriethoxysilane
500
5
-
6.7
GFAAS
[26]
Amberlite XAD-7
Quinolin-8-ol
20
10
-
5.2
HG-ICP-AES
[27]
Activated carbon
Thiourea-Bromide
170
250
200-31300
104.5
Spectrophotometry
[13]
Alumina
MBT
12
100
40 -1250
2.7
HGAAS
This work
LOD: limit of detection, PF: preconcentration factor, APDC: Ammonium pyrolidinedithiocarbamate, 5-Br-PADAP: 2-(5-Bromo-2-pyridylazo)-5-diethyl aminophenol.
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