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Enrichment-separation and determinations of cadmium(II) and lead(II)-1-phenyl-1H-tetrazole-5-thiol chelates on Diaion SP-207 by solid phase extraction-flame atomic absorption spectrometry
⁎Corresponding author. Tel./fax: +90 3524374929. soylak@erciyes.edu.tr (Mustafa Soylak)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
A separation–enrichment system based on adsorption of cadmium(II) and lead(II) ions as their 1-phenyl-1H-tetrazole-5-thiol chelates on Diaion SP-207 polymeric resin has been established. Flame atomic absorption spectrometry was used for the determination of cadmium and lead. Analytes were recovered (>95%) on 0.5 g Diaion SP-207 at pH 6.5 and 4.5 mg of 1-phenyl-1H-tetrazole-5-thiol at 1.5 ml min−1 flow rate. Cadmium and lead were desorbed by 10 ml of 1 M CH3COOH. The influences of some 1A and 2A group metals, transition metals on the recoveries of analyte were also investigated. Addition/recovery tests were performed. The accuracy was checked by the analysis of TMDA 54.4 fortified lake water certified reference material. The proposed procedure was applied for the analysis of analyte in real samples with successful results.
Keywords
1-Phenyl-1H-tetrazole-5-thiol
Diaion SP-207
Preconcentration
Solid phase extraction
Determination
1 Introduction
Metals at trace levels still represent a group of dangerous pollutants, to which close attention is paid (Dogan et al., 2002; Babula et al., 2008; Massanyi et al., 2001; Daka et al., 2008). Cadmium and lead are problematic elements for plants, animals and humans. Cadmium and lead are toxic at trace levels due to disrupting enzyme functions, replacing essential metals in pigments or producing reactive oxygen species (Babula et al., 2008; Massanyi et al., 2001; Daka et al., 2008). In the determination of trace metals by instrumental analytical techniques, lower analyte levels than the quantification limits of instrument and the interference of saline components are generally two main limitations (Babula et al., 2008; Massanyi et al., 2001; Aksuner et al., 2011; Khan et al., 2011). To solve these limitations, separation–enrichment procedures like solvent extraction (Helena et al., 1999; Nishimoto and Wagatsuma, 2009), electro deposition (Kanchi et al., 2011; Zhao et al., 2010; Liu and Dai, 2010), cloud point extraction (Ojeda et al., 2010; Borkowska-Burnecka et al., 2010; Baig et al., 2010), membrane filtration (Soylak et al., 2007; Itoh et al., 1996), coprecipitation (Aydin and Soylak, 2007; Doner and Ege, 2005), microextraction (Gharehbaghi and Shemirani, 2010; Shirkhanloo et al., 2010; Salahinejad and Aflaki, 2011) etc are continuously used by analytical chemists around the world.
Solid phase extraction is also used for this purpose (Elci et al., 2000; Soylak et al., 2004; Oral et al., 2011; Armagan et al., 2002; Al-Fifi et al., 2009). It is one of the important enrichment/separation methodologies for the trace heavy metal ions (Soylak et al., 1996a,b; Escudero et al., 2010; Soleimani and Khani, 2010). Natural and synthetic solid phase extractors that have high surface area and adsorption capacity, stable for acidic and basic media are preferred for solid phase extraction of metal ions. Zeolites, wool and diatom soils are natural materials and polymeric resins like Amberlite XAD, Ambersorb, and Diaion are also some artificial materials. Diaion SP-207 is brominated styrene–divinylbenzene polymers, and has relatively hydrophobic nature. Its mesh size, surface area, and pore size are 20–60 mesh, 650 m2 g−1, and 105 Å, respectively (http://www.sigmaaldrich.com).
1-phenyl-1H-tetrazole-5-thiol was used as chelating agent for presented work. It was used for accurate spectrophotometric determinations of palladium and bismuth ions at trace levels (http://www.sigmaaldrich.com). According to our literature scanning, until now, 1-phenyl-1H-tetrazole-5-thiol and Diaion SP-207 resin combination is not used for the solid phase extraction studies.
In this work, a simple and accurate procedure for cadmium(II) and lead(II) ions that is based on solid phase extraction of cadmium(II) and lead(II) as their 1-phenyl-1H-tetrazole-5-thiol on Diaion SP-207 resin.
2 Experimental
2.1 Reagents and solutions
High purity reagents from Merck, Darmstadt were used. Stock solutions containing 1000 mg l−1 analyte were prepared from nitrate salts of cadmium and lead ions in 1% of HNO3. Diluted standard solutions and model solutions were daily prepared from the stock standard solutions. Diaion SP-207 is purchased from Sigma, St. Louis, USA (Supelco no: 13623-U). It was washed successively with NaOH, water, 3 mol l−1 HNO3 and water, sequentially. 0.3% (m/V) solution of 1-phenyl-1H-tetrazole-5-thiol (Sigma Chem. Co., St. Louis) was prepared by dissolving in ethanol. The buffer solutions given in the Literature (Soylak et al., 1996a,b) were used in the presented work. TMDA 54.4 fortified lake water certified standard reference material was supplied by National Water Research Institute, Environment Canada (Burlington, ON, Canada). Synthetic seawater was prepared according to the literature (http://www.thelabrat.com/protocols/SyntheticSeaWater.shtml).
2.2 Instrument
A Perkin-Elmer Model 3110 atomic absorption spectrophotometer equipped with a 10-cm air-acetylene burner was used for the determination of the metal ions. All instrumental settings were those recommended in the manufacturer’s manual book. The samples were introduced to nebulizer of the AAS by using micro injection system (Berndt and Jackwerth, 1975; Soylak et al., 2008). A pH meter, Sartorius PT-10 Model glass-electrode was employed for measuring pH values in the aqueous phase. A column (15.0 cm in length and 1.0 cm in diameter), packed with 0.5 g of Diaion SP-207 was used.
2.3 Procedure
Twenty five milliliters of reverse osmosis water containing 5–20 g of analytes was placed in a beaker. Five milliliters of buffer solution to give the desired pH between 3-8 and 1-phenyl-1H-tetrazole-5-thiol solution was added. After 10 min, the solution was passed through to Diaion SP-207 column. The adsorption of metal chelates is performed. Then adsorbed analytes on the resin were desorbed by 10 ml of 1 mol l−1 CH3COOH. The eluent content was evaporated to 2 ml. Hundred microliters of the solution was introduced to the nebulizer of the flame AAS by micro injection system to determine analyte elements (Berndt and Jackwerth, 1975; Soylak et al., 2008).
2.4 Analysis of water samples
The method was also applied to TMDA-54.4 fortified lake water certified reference materials. The separation-preconcentration procedure given above was applied to 10.0 ml of TMDA-54.4 fortified lake water sample.
Natural waters were collected in prewashed polyethylene bottles. The pH of 75 ml of the sample was adjusted to 6.5 with buffer. Then the separation–enrichment procedure given above was applied to the final solutions. Then analyte element contents were determined by flame AAS.
3 Results and discussion
3.1 Influences of pH
At the big ratio metal chelates are used and metal chelates generally occurred at the buffered pH medium (Soylak et al., 2011, 1999; Bouariche et al., 2010; Baig et al., 2009; Ghaedi et al., 2009a,b; Chang et al., 2010), the effects of pH of the aqueous medium were investigated for recoveries of cadmium(II) and lead(II)-1-phenyl-1H-tetrazole-5-thiol chelates on Diaion SP-207 resin at the pH range of 3.0–8.0 by using model solutions containing 5 μg of cadmium(II) and 20 μg of lead(II). The results are depicted in Fig. 1. Quantitative recovery values were obtained at the pH range of 6.0–7.0. All other works were done at pH 6.5 by using phosphate buffer.
The influences of the pH on the recoveries of cadmium(II) and lead(II) ions (N = 3).
3.2 Amounts of ligand
The influences of amounts of 1-phenyl-1H-tetrazole-5-thiol on the retentions of Cd(II) and Pb(II) on Diaion SP-207 resin were also studied. The results for analyte ions are depicted in Fig. 2. The recoveries of both ions were quantitative (>95%) after 4.5 mg of 1-phenyl-1H-tetrazole-5-thiol. 4.5 mg of 1-phenyl-1H-tetrazole-5-thiol was used for all other experiments. (See Fig. 3).
Effects of amounts of 1-phenyl-1H-tetrazole-5-thiol on the recoveries of cadmium(II) and lead(II) ions (N = 3).
Relations between sample volume and recoveries (N = 3).
3.3 Eluent type
The influences of various eluents given in Table 1 were examined for desorption of adsorbed metal ion chelates from Diaion SP-207 resin. Quantitative results (95%) were obtained for both cadmium and lead with 1 mol l−1 acetic acid, 1 mol l−1 HNO3 and 1 mol l−1 HCl. Ten microliters of 1 mol l−1 acetic acid was selected. (See Table 2).
Eluent type
Recovery, (%)
Cd
Pb
1 mol l−1 CH3COOH
99 ± 2
98 ± 1
2 mol l−1 CH3COOH
99 ± 2
89 ± 1
3 mol l−1 CH3COOH
100 ± 2
76 ± 3
1 mol l−1 HNO3
99 ± 0
95 ± 3
2 mol l−1 HNO3
92 ± 2
77 ± 1
3 mol l−1 HNO3
92 ± 2
74 ± 2
1 mol l−1 HCl
100 ± 1
99 ± 1
2 mol l−1 HCl
89 ± 1
75 ± 2
3 mol l−1 HCl
90 ± 3
89 ± 1
Ion
Added as
Concentration (μg ml−1)
Recovery, (%)
Cd
Pb
Na+
NaCl
10,000
96 ± 2
102 ± 3
Mg+2
Mg(NO3)2
500
96 ± 2
97 ± 2
Ca+2
CaCl2
2000
98 ± 1
103 ± 1
K+
KCl
10,000
97 ± 3
95 ± 2
Na2SO4
2500
98 ± 3
97 ± 2
Cl−
NaCl
10,000
96 ± 2
100 ± 2
Pb+2
Pb(NO3)2
5
98 ± 2
–
Cd+2
Cd(NO3)2
1
–
100 ± 2
Fe+3
Fe(NO3)3·9H2O
5
98 ± 2
102 ± 3
Ni+2
Ni (NO3)2·6H2O
5
97 ± 1
100 ± 0
3.4 Flow rates
Because the flow rates of sample solution and eluent solutions are two important parameters for the quantitative retention of analytes on the solid phase extraction works (Soylak et al., 1997; Ghaedi et al., 2005; Soylak, 2004; Kamau et al., 2011), the effects of sample and eluent flow rates on the recoveries of Cd(II) and Pb(II)-1-phenyl-1H-tetrazole-5-thiol chelates in the range of 1.5–6.0 ml min−1. The recoveries of Cd(II) and Pb(II) were quantitative till 2.0 ml min−1. For all further studies for sample and eluent flow rates, 1.5 ml min−1 were used.
3.5 Sample volume
The effect of the sample volume on the recoveries of cadmium and lead ions as 1-phenyl-1H-tetrazole-5-thiol on Diaion SP-207 resin was examined in the sample volume range of 50–300 ml (Fig. 2). While the recoveries of cadmium ions were quantitative till 200 ml, lead ions were recovered quantitatively till 75 ml. Due to the quantitative recovery values (>95%) were obtained at 75 ml for both analyte ions, the preconcentration factor is calculated by the ratio of the highest sample volume for both analyte ions (75 ml) and the lowest final volume (2.0 ml). In the present study to achieve the highest possible preconcentration the factor was 37.5.
3.6 Interferences
On the spectroscopic determination of metals, highly saline solutions are affected by the analyte levels, this is known as “Matrix Effect” (Soylak et al., 1996a,b; Ghaedi, 2006; Soylak and Tuzen, 2006; Soylak et al., 2003; Divrikli et al., 2003; Munagapati et al., 2010; Ghaedi et al., 2010; Soylak and Yilmaz, 2011). The influences of the alkaline, alkaline earth and transition metal ions were examined. The results are given in Table 1. The limit of tolerance for analytes is defined as the ion concentration causing a relative error smaller than ±5% related to the enrichment, separation and determination of analytes.
3.7 Figure of merits
The calibration curves were linear in the range of 0.02–1.5 μg ml−1 for cadmium and 0.5–8.0 μg ml−1 for lead. The regression equations were A = 0.140C + 0.002 (R2 = 0.999) for cadmium and A = 0.009C−0.001 (R2 = 0.999) for lead. The detection limits for cadmium(II) and lead(II) were calculated after presented solid phase extraction procedure was applied to the blank solutions. The limits of detection for cadmium and lead (k = 3, N = 10) were 1.1 μg l−1 and 48 μg l−1, respectively.
Various amounts of cadmium and lead ions were spiked to various water samples given in Table 3. The presence of natural waters has no significant influences on the recovery of cadmium and lead ions on Diaion SP-207 resin. BDL: Below the detection limit.
Added (μg)
Tap water
Bottled Mineral Water
Found (μg)
Recovery, (%)
Found (μg)
Recovery, (%)
Cd
0
BDL
BDL
2,5
2.4 ± 0.1
97
2.6 ± 0.2
102
5
5.0 ± 0.0
100
5.0 ± 0.2
100
10
9.9 ± 2.0
99
9.8 ± 0.5
98
Pb
0
BDL
BDL
2,5
2.5 ± 0.1
100
2.4 ± 0.1
98
5
5.0 ± 0.1
100
4.8 ± 0.1
97
10
10.0 ± 0.2
100
10.1 ± 0.1
101
Added (μg)
Synthetic seawater
Found (μg)
Recovery, (%)
Cd
0
BDL
10
10.2 ± 0.0
102
20
20.0 ± 0.6
103
Pb
0
BDL
10
10.4 ± 0.0
104
20
19.4 ± 0.0
98
3.8 Application of the method
The accuracy of methodology was checked by certified reference material. As shown in Table 4, good and quantitative recoveries are obtained. This is an important point for the application of the presented method to natural water samples. The presented solid phase extraction method was applied to some water samples from Kayseri Turkey. The results are given in Table 5. BDL: Below the detection limit.
Element
Found (μg l−1)
Certified value (μg l−1)
Recovery, (%)
Pb
493.5 ± 0
514
96
Cd
164 ± 4
158
104
Sample
Concentration (μg l−1)
Cd
Pb
Tap water from Kayseri city
BDL
BDL
Bottled mineral water
BDL
BDL
Waste water from a factory
27.4 ± 0.0
530 ± 56
Waste pool water
26.5 ± 1.9
53.0 ± 0.0
4 Conclusion
A new simple, precise and accurate solid phase extraction method has been established in the presented work. The effect of some analytical parameters like pH, amounts of reagents and concomitant ions are tolerable. The presented procedure was successfully applied to natural water samples from Kayseri Turkey to determine the level of lead and cadmium in these samples. The performance of this work was compared with some enrichment works in Table 6. The detection limit of this work is better than some of them in Table 6. Lower detection limits of some other works are related with higher sensitivity of the instrument used in these studies. The presented method is also comparable to other methods described in the literature based on high tolerance to matrix ions. FAAS: Flame atomic absorption spectrometry; ICP-OES: Inductively coupled plasma optical emission spectrometry; CoP: Coprecipitation; CPE: Cloud point extraction; DLLME: Dispersive liquid–liquid microextraction; MF: Membrane filtration; LOD: Limit of detection.
Method
Instrument
Conditions
LOD, μg l−1
Ref.
CoP; Aluminum hydroxide
FAAS
pH 7
Cd:6, Pb: 16
Doner and Ege (2005)
CPE; Triton X-114; bis((1H-benzo [d] imidazol-2yl)ethyl) sulfane
FAAS
pH 8
Cd: 1.4, Pb: 2.8
Ghaedi et al. (2009b)
DLLME; Ammonium pyrrolidine dithiocarbamate
ICP-OES
pH 6
Cd: 0.8
Salahinejad and Aflaki (2011)
MF; Carmine; cellulose nitrate membrane filter
FAAS
pH 9
Cd: 0.08, Pb: 0.93
Soylak et al. (2007)
SPE; Diaion SP-207
FAAS
pH 6.5; Eluent: 1 mol l−1 acetic acid
Cd: 1.1, Pb: 48
Presented work
Acknowledgement
The authors are grateful for the financial support of the Unit of the Scientific Research Project of Erciyes University. Zeynep Topalak would like to thank to Erkan Yilmaz for his helps. Prof. Dr. Mustafa Soylak also thanks the King Saud University for Visiting Professor Program.
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