Environ Chem Lett (2011) 9:115–119 DOI 10.1007/s10311-009-0254-6
ORIGINAL PAPER
Determination trace amounts of copper, nickel, cobalt and manganese ions in water samples after simultaneous separation and preconcentration Daryoush Afzali • Sayez Zia Mohammadi
Received: 17 May 2009 / Accepted: 20 October 2009 / Published online: 6 November 2009 Ó Springer-Verlag 2009
Abstract In the present article, a simple, rapid, sensitive and economical method has been developed for the simultaneous separation and preconcentration of the trace amounts of copper, nickel, cobalt and manganese in water samples by using modified XAD-4 resins. The sorption was quantitative in the pH range 6.0–9.0, whereas quantitative desorption occurred instantaneously with 5.0 mL of 2 M HNO3, and selected elements have been determined by using flame atomic absorption spectrometry. Dynamic ranges were 0.04–3.5, 0.1–6.0, 0.04–4.5 and 0.04–4.0 lg/ mL for copper, nickel, cobalt and manganese, respectively. The detection limits were 9.2, 28.6, 12.3 and 5.7 ng/mL for Cu(II), Ni(II), Co(II) and Mn(II), respectively. The effects of the experimental parameters, including the sample pH, eluent type, interference ions and breakthrough volume, were studied for separation and preconcentration of Cu(II), Ni(II), Co(II) and Mn(II) ions. Determination of these ions in standard samples confirmed that the proposed method has good accuracy. The proposed method was used for the determination of these ions in water samples. Keywords Separation Heavy metal determination Preconcentration Sorbent
D. Afzali (&) Environment Department, Research Institute of Environmental Sciences, International Center for Science, High Technology and Environmental Sciences, Kerman, Iran e-mail:
[email protected] S. Z. Mohammadi Department of Chemistry, Payame Noor University, Bam, Iran
Introduction Due to the industrial facilities, heavy metal contents in environmental samples unfortunately increase. So, it is very important and necessary to develop reliable, fast and sensitive methods for the determination of heavy metals in environmental and biological samples. Several techniques such as neutron activation analysis (Zecca et al. 2001), energy dispersive X-ray fluorescence spectrometry (Eksperiandova et al. 2002), inductively coupled plasmaatomic emission spectrometry (Rao et al. 2002), atomic absorption spectrometry using either flame (Chen and Teo 2001) or electro thermal atomization (Lin et al. 2001), chromatography (Ding et al. 2000), electroanalytical techniques (Lu et al. 2000) and UV–vis spectrophotometry (Li et al. 2002), have been used for the multielement analysis in different matrices. Most of these methods necessitate using rather sophisticated and high cost operated instruments. Determination of trace heavy metals, such as copper, nickel, cobalt and manganese in various samples, is very important. The direct determination of the trace heavy metals in environmental waters by atomic absorption spectrometry is very difficult due to the low levels of metal ions and also interfere influences of main components of the water samples. One way to solve this problem is separation and preconcentration in order to enhance the detection limit and selectivity and thereby improve the precision and accuracy of analytical results. Solid phase extraction is one of the several techniques that are used for this purpose. The solid-phase extraction process has received more acceptances due to a number of possible advantages including availability and easy recovery of the solid-phase, high preconcentration factors and easiness of separation and enrichment using continuous flow systems (Mester and
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Sturgeon 2003). The most common technique available for this purpose is solid-phase extraction using various adsorbents such as thiol cotton, activated carbon, cellulose, polythioether, microcrystalline naphthalene, synthetic Zeolites, modified kaolinite and analcime Zeolites (Afzali et al. 2007). Some of these sorbents may be fairly effective for preconcentration of metal ions, but their methods of preparation are lengthy and involve rigid control of conditions. Amberlite XAD resins have been also used for the preconcentration of trace metal ions from different water samples (Butler et al. 2009). Amberlite XAD-4 resin is a well-known member of Amberlite XAD resins and has found widespread application for the separation and preconcentration of trace metals ions (Uzun et al. 2001; Tuzen et al. 2005), because it has good physical and chemical properties such as porosity, high surface area, durability and purity (Elci et al. 1992). In the present work, a simple, sensitive and rapid simultaneous separation and preconcentration method using an Amberlite XAD-4 resin column has been established prior to flame atomic absorption spectrometric (FAAS) determination of trace amounts of Cu(II), Ni(II), Co(II) and Mn(II) ions in water samples.
Experimental
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the reagent by passing 5 mL of 0.5% Aluminon solution in ethanol. Afterward, it was washed with 10 mL of deionized water until reagent excess was eliminated from the resin. All experiments were done in a funnel-tipped glass tube (60mm 9 6 mm) as a column for preconcentration. It was plugged with polypropylene fibers and then filled with the XAD-4 resin. Before sample loading, the column must be preconditioned by passing a buffer solution. Then, the column could be used repeatedly for twenty times at least. General procedure Aliquots of copper, nickel, cobalt and manganese (0.2–17.5, 0.5–30.0, 0.2–22.5 and 0.2–20.0 lg for copper, nickel, cobalt and manganese) were taken in a 50 mL beaker. The total volume of the metal ions solution was made up approximately to 30 and 5 mL of buffer solution with pH 7.0 was added to it. Then, this solution was passed through the column at a flow rate of approximately 2 mL/min. At the end, the column was washed with 5 mL of deionized water. The adsorbed metal ions on the column were eluted with 5.0 mL of 2 M nitric acid solution at flow rate of 1 mL/min. The eluent was collected in a 5.0 mL volumetric flask. The final solution was aspirated directly into the flame atomic absorption spectrometer against the blank prepared in the same manner without the addition of metal ions.
Apparatus and reagents Result and discussion A Varian model SpectrAA 220 atomic absorption spectrometer was used for measuring Cu(II), Ni(II), Co(II) and Mn(II) in air–acetylene flame. A Beckman pH meter was employed for pH measurements. A funnel-tipped glass tube (60mm 9 6 mm) was used as a column for preconcentration. The stock solutions of Cu(II), Ni(II), Co(II) and Mn(II) were prepared by dissolving 1.000 g of copper, nickel, cobalt and manganese metal strip 99.99% Merck (Darmstadt, Germany) in 20 mL 1:1 nitric acid and diluted to 1,000.0 mL. Working solutions were prepared by appropriate dilution of the stock solutions. XAD-4 was purchased from Serva (New York, USA) with particle size ´˚ of 0.1–0.2 mm, pore diameter 100 A and surface area 750 m2/g. A 0.5% solution of Aluminon in ethanol was prepared. Preparation of Amberlite XAD-4 column loaded with Aluminon Amberlite XAD-4 was treated with an ethanol 95%/1 M of hydrochloric acid/water (2:1:1) solution overnight. The resin was rinsed with 10 mL of deionized water. Packing of the column must be done using ethanol as eluent since water makes resin beads float. The resin was saturated with
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Reaction conditions The reaction conditions were investigated with 5.0 lg of each ion, individually. Adsorptions studies were carried out at different pHs, keeping the other variables constant. It was found that the copper, nickel, manganese and cobalt were quantitatively adsorbed on resin in the pH range 6.0–9.0. In subsequent studies, the pH was maintained approximately 7.0. Addition of 2–10 mL of buffer did not have any effect on the adsorption. Therefore, 5 mL of the phosphate buffer pH * 7 was used in all subsequent experiments. In order to test of sample volume on the recovery, different volumes (30–1,200 mL) of test solutions containing 5.0 lg of each ion were enriched on the column. It was observed that absorbances were almost constant up to 1,000 mL of the aqueous phase. However, for convenience, all the experiments were carried out with 30 mL of the aqueous phase. A number of eluent were tested to be desorbed metal ions from the column. Organic solvents can be used as eluent, but they removed the Aluminon reagent from the column. If acid solutions were used as eluent, the reagent
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was retained on the column and therefore, allowed using the column several times. Preliminary observations indicated that 2 M HNO3 desorbed these metal ions better than 2 M HCl and H2SO4. Hence, 5.0 mL of 2 M nitric acid was used in the present work. The flow rate of the sample was varied from 0.5 to 10 mL/min. It was found that a flow rate of 0.5–3.5 mL/min did not affect on the retention of ions. Therefore, a flow rate of 2 mL/min was used in all experiments. The flow rate of eluent was varied from 0.2 to 3.0 mL/min. It was found that a flow rate of 0.2–1.5 mL/min did not affect their desorption ions. Therefore, a flow rate of 1 mL/min was used in all experiments.
Effect of different ions Various ions were added individually to a solution containing 5.0 lg of each ion, and the general procedure was applied. The tolerance limit was set as the concentration of the diverse ion required to cause ±4% error. The results obtained are given in Table 1. Among the cations and anions examined most could be tolerated up to gram or milligram levels except EDTA that interfered seriously because of the higher constants of the metal–EDTA complexes than of the Aluminon–metal complexes. Thus, the proposed method is selective and can be used for determination of these ions in environmental samples. Determination of copper, nickel, cobalt and manganese ions in pond sediment
Calibration and sensitivity Under the optimized conditions, calibration curves were constructed for the determination of copper, nickel, cobalt and manganese according to the general procedure (Fig. 1). Linearity in final solution was maintained between 0.04 and 3.5, 0.1 and 6.0, 0.04 and 4.5, and 0.04 and 4.0 lg/mL for copper, nickel, cobalt and manganese with correlation factors 0.9997, 0.9999, 0.9998 and 0.9999, respectively. Seven replicate determinations of 1.0 lg/mL copper, nickel, cobalt and manganese in a mixture give a mean absorbance of 0.1592, 0.1007, 0.0863 and 0.1966 with relative standard deviation ±1.4, ±1.2, ±1.3 and ±1.5%, respectively. Therefore, it is possible to retain 0.2 lg of Cu(II), 0.5 lg of Ni(II), 0.2 lg of Co(II) and 0.2 lg of Mn(II) from 1,000 mL of solution (preconcentration factor of 200) and elution with 5.0 mL of HNO3 gives a concentration of 0.2, 0.5, 0.2 and 0.2 ng/mL for copper, nickel, cobalt and manganese in initial solution, respectively.
The accuracy and applicability of the proposed method has been applied to the determination of these metal ions in National Institute for Environment Studies (NIES) No. 2 pond sediment. A 0.10 g sample was taken in a beaker and dissolved in concentrated nitric acid (*5 mL) with heating. The solution was cooled, diluted and filtered. The filtrate was made to 100.0 mL with distilled water in a Table 1 Effect of diverse ions Ion
Tolerance limit (mg)
NH4?
800
NO3-, CH3COO-
700
I-
500
SO42-
400
SCN-
80
H2PO4HPO42-
100
Cl
1,200
S2O32-
30
C2O42-
50
EDTA 0.8
A
0.6
0.4
Cu Ni Co Mn
0.2
0 0
1
2
3
4
5
6
Concentration (ppm) Fig. 1 Calibration curve. Conditions: buffer, 5 mL; flow rate of sample, 2 mL/min; final solution, 5.0 mL of 5 M HNO3 solution; flow rate of eluent, 1 mL/min; and reference, reagent blank
2-
100
0.1
Na?
1,000
Ca2?
100
Mg2? Al3?
30 80
Mo2?
5
Bi3?
2
Pb2?
4
Fe3?
5
Cr3?
2
Hg2?
5
3?
2
Sb
Conditions: 5.0 lg of each ion in final solution; buffer, 5 mL; flow rate of sample, 2 mL/min; final solution, 5.0 mL of 5 M HNO3 solution; flow rate of eluent, 1 mL/min; and reference, reagent blank
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Table 2 Determination of Cu, Ni, Co and Mn ions in certified reference materials Sample
Composition (% or lg/g)
Founda
NIES, No. 2 pond sediment
Al, 10.6 ± 0.5; Fe, 6.53 ± 0.35; Ca, 0.81; K, 0.68; Na, 0.57%; Zn, 343; Cu, 210; Pb, 105; Cd, 0.82; Ni, 40;
Cu: 210.0 ± 6.6 lg/g Ni: 40.2 ± 1.3 lg/g
Cr, 75; Co, 27; and Mnb, 50.0 lg/g
Co: 26.7 ± 0.9 lg/g Mn: 49.9 ± 1.7 lg/g Ni: 40.2 ± 1.3 lg/g
NKK No. 920 aluminum alloy
Bi, 0.06; Ti, 0.15; Zn, 0.80; Sn, 0.20; Ga, 0.05; Pb, 0.10; Fe, 0.72; Ca, 0.03; Mg, 0.46; Co, 0.10; Sb, 0.10; Mn, 0.20; Ni, 0.29; V, 0.15; Cu, 0.71; Cr, 0.27; and Si, 0.78%;
Cu: 0.70 ± 0.04% Ni: 0.30 ± 0.02% Co: 0.101 ± 0.006% Mn: 0.20 ± 0.01%
Conditions were the same as Table 1 a
Mean ± standard deviation (N = 4)
b
Manganese was added
Table 3 Analysis of Cu, Ni, Co and Mn ions in water samples Sample
Element
Recommended procedurea (ng/mL)
GFAASa determination (ng/mL)
Spring water (Rayen, Kerman)
Cu
4.50 ± 0.06
4.58 ± 0.05
River water (Rayen, Kerman)
River water (Kohpayeh, Kerman)
Ni
3.08 ± 0.03
3.13 ± 0.05
Co
2.50 ± 0.03
2.48 ± 0.03
Mn Cu
3.60 ± 0.05 5.20 ± 0.08
3.57 ± 0.06 5.16 ± 0.07
Ni
4.30 ± 0.06
4.26 ± 0.05
Co
5.25 ± 0.07
5.29 ± 0.06
Mn
7.22 ± 0.10
7.19 ± 0.10
Cu
5.64 ± 0.07
5.61 ± 0.07
Ni
5.08 ± 0.08
5.12 ± 0.06
Co
4.41 ± 0.06
4.40 ± 0.06
Mn
6.06 ± 0.09
6.10 ± 0.08
Conditions were the same as Table 1 a
Mean ± standard deviation (N = 5)
calibrated flask. An aliquot of the sample solution was taken individually, and these metal ions were determined by the general procedure. The results are given in Table 2 and are in good agreement with the certified value.
sample solution was taken individually, and these metal ions were determined by the general procedure. The results obtained are given in Table 2 and are in good agreement with the certified value.
Determination of copper, nickel, cobalt and manganese ions in standard alloy
Determination of Cu(II), Ni(II), Co(II) and Mn(II) ions in water samples
The accuracy and applicability of the proposed method has been applied to the determination of these metal ions in Nippon Keikinzoku Kogyo (NKK) CRM 920 Aluminum alloy. A 0.010 g sample of the standard alloy was taken in a beaker and dissolved in a mixture of concentrated HNO3/ HCl (1:1) with heating on a water bath. The solution was cooled, filtered if needed and diluted to 100.0 mL with distilled water in a calibrated flask. An aliquot of the
The method has been employed for the determination of these metal ions in spring and river water samples. A 250.0 mL water sample was adjusted to pH 1.5 with nitric acid, filtered to remove suspended material, and general procedure was applied. In order to compare the proposed method, the actual water samples were analyzed by graphite furnace atomic absorption spectrometer (GFAAS). The results were given in Table 3.
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Conclusion The aim of this study was to develop a suitable method for simultaneous separation and preconcentration of trace amounts of Cu(II), Ni(II), Co(II) and Mn(II) ions in various samples with a recovery percent better than 96%. The results of our study indicate that the procedure proposed, consisting of preconcentration of Cu(II), Ni(II), Co(II) and Mn(II) followed by FAAS measurement in the aqueous phase, can accurately determine these metal ions in various aqueous samples. The main advantages of this procedure are (1) the proposed method is sensitive and selective, (2) it offers advantages like reliability and reproducibility in addition to its simplicity and suffers from less interference, (3) the preparation of the extractor system is simple and fast, (4) during desorption, the Aluminon reagent remains in the column, which allows to use the column several times and (5) good enrichment factor (200) can be achieved.
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