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Cloud point extraction and simultaneous determination of zirconium and hafnium using ICP-OES
Journal of Colloid and Interface Science 298 (2006) 419–425 www.elsevier.com/locate/jcis
Cloud point extraction and simultaneous determination of zirconium and hafnium using ICP-OES Shahab Shariati, Yadollah Yamini ∗ Department of Chemistry, Faculty of Sciences, Tarbiat Modarres University, P.O. Box 14115-175, Tehran, Iran Received 22 September 2005; accepted 1 December 2005 Available online 9 January 2006
Abstract In the present study a simple versatile separation method using cloud point procedure for extraction of trace levels of zirconium and hafnium is proposed. The extraction of analytes from aqueous samples was performed in the presence of quinalizarine as chelating agent and Triton X-114 as a non-ionic surfactant. After phase separation, the surfactant-rich phase was diluted with 30% (v/v) propanol solution containing 1 mol l−1 HNO3 . Then, the enriched analytes in the surfactant-rich phase were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The different variables affecting the complexation and extraction conditions were optimized. Under the optimum conditions (i.e. 3.4 × 10−5 mol l−1 quinalizarine, 0.1% (w/v) Triton X-114, 55 ◦ C equilibrium temperature) the calibration graphs were linear in the range of 0.5–1000 µg l−1 with detection limits (DLs) of 0.26 and 0.31 µg l−1 for Zr and Hf, respectively. Under the presence of foreign ions no significant interference was observed. The precision (%RSD) for 8 replicate determinations at 200 µg l−1 of Zr and Hf was better than 2.9% and the enrichment factors were obtained as 38.9 and 35.8 for Zr and Hf, respectively. Finally, the proposed method was successfully utilized for the determination of these cations in water and alloy samples. © 2005 Elsevier Inc. All rights reserved. Keywords: Cloud point extraction; Zirconium; Hafnium; Quinalizarine; Triton X-114
1. Introduction Zirconium (Zr) and hafnium (Hf) are strategic elements and their identification and determination are very important. Zr is used for removing sulfur, nitrogen and oxygen from steel and in the copper manufacturing. Its alloys are employed in the production of optical glasses with high refractive index and in the ceramic industry to produce enamels. Also its transparency to thermal neutrons has made Zr a good structural material in nuclear reactors and chemical plants. Hafnium is found combined in natural zirconium compounds but does not exist as a free element in nature. Minerals that contain zirconium, such as alvite [(Hf, Th, Zr)SiO4 ·H2 O], thortveitite and zircon (ZrSiO4 ), usually contain between 1 and 5% hafnium. It has been found to be a good absorber of neu* Corresponding author. Fax: +98 21 88006544.
E-mail address: [email protected] (Y. Yamini). 0021-9797/$ – see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.12.005
trons, leading to its use as a moderator in control rods for nuclear reactors. It is also used in the manufacture of the filaments for electric light bulbs. Due to lanthanide contraction, Zr and Hf are similar in chemistry and exist together in nature [1–3]. The determination of very low concentrations of Zr and Hf usually requires separation and pre-concentration steps. The methods for separation of these elements are based on tiny differences in stabilities of metal complexes. In order to determine Zr, different spectroanalytical techniques were used [4]: Laser ablation inductively coupled plasma optical emission spectrometry LAICP-OES [5], inductively coupled plasma mass spectrometry ICP-MS [6], X-ray fluorescence [7], also one-step procedures such as reversedphase liquid chromatographic separation (RP-LC) [8] or chelating ion exchange followed by spectrophotometric detection [9] have been reported. The detection limits of the above methods for determination of Zr varied in the range of 0.1–3 mg l−1 .
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Similarly, Hf was determined by ICP-OES [10,11], ICPMS [12] and neutron activation analysis [13] methods. The detection limits of all methods mentioned above were in the range of 2–30 µg l−1 . Also, the simultaneous determination of these two elements was carried out by energy dispersive X-ray fluorescence after solid phase pre-concentration [14], liquid chromatography separation and determination of their hydroxamic acid chelates [15], ternary complexes of them with 2(5-bromo-2-pyridylazo)-5-diethylamino phenol (5-Br-PADAP) and fluoride without extraction [4] and after solid phase extraction [16], also separation using N -benzoyl-N -phenyl hydroxyl amine (BPHA) supported on a microporous polymeric resin [17], coprecipitation with Ti(OH)4 –Fe(OH)3 [18] followed by ICP-OES determination and the spectrophotometric method assisted by chemometric procedures have been proposed [19]. Separations and pre-concentrations based on the cloud point extraction (CPE) are becoming an important and practical application of using surfactants in analytical chemistry. The CPE has been used successfully for the pre-concentration of species of widely differing character and nature, such as metal ions, proteins and other biomaterials or organic compounds of strongly differing polarity. In this method, any component originally present in the solution that interacts with the micellar aggregate either directly (generally hydrophobic organic compounds) or after a previous derivatization reaction (i.e. metal ions after reaction with a suitable hydrophobic ligand) can thus be extracted differently, (depending on the micelle–solute binding interactions) from the initial solution and concentrated in the small volume of the surfactant-rich phase. The small volume of the surfactant-rich phase obtained with this method (generally between 100 and 400 µl) permits the design of extraction schemes that are simple, cheap, efficient and safe in comparison with liquid–liquid extraction methods [20–27]. The mechanism by which separation occurs is poorly understood. Some authors have proposed that it would be due to an increase in the micellar aggregation number when temperature is increased [28,29]. Others have suggested that the phase separation mechanism would be caused by a change in micellar interactions, which are repulsive at low temperatures but predominantly attractive at high temperatures [30]. Other authors have explained the cloud point phenomenon on the basis of the dehydration process that occurs in the external layer of the micelles of non-ionic surfactants when temperature is increased [31]. Also, dielectric constant of water decreases by increasing temperature, rendering it to a poorer solvent for the hydrophobic portion of the surfactant molecule [32]. In the present work, the cloud point extraction has been developed and optimized for the extraction and pre-concentration of Zr(IV) and Hf(IV) in water samples. For this purpose, Zr(IV) and Hf(IV) form chelates with quinalizarine and resultant complexes pre-concentrate using octyl phenoxypolyethoxy ethanol (Triton X-114) as a non-ionic surfactant. Finally, simultaneous determinations of these elements were performed by ICPOES and the proposed method was applied to the real samples.
2. Experimental 2.1. Reagents and materials All chemicals used were of analytical reagent grade. Zr stock solution (1000 mg l−1 ) was prepared by the direct dissolution of ZrOCl2 ·8H2 O (99.5%) in double distilled water. The stock solution of Hf (1000 mg l−1 ) was purchased from Merck (Darmstadt, Germany). These standard solutions were diluted with distilled water to prepare mixed stock solutions in such a way that the concentration of the mixtures was 10 and 100 mg l−1 inspect of Zr and Hf, respectively. All required solutions were freshly prepared by diluting the mixed standard solution with buffer solution to the required concentration after the addition of ligand and surfactant. Reagent grade 1,2,5,8-tetrahydroxyanthraquinone (quinalizarine) from Merck was used as chelating agent. The standard solution of quinalizarine (10−3 mol l−1 ) was prepared by dissolving proper amounts of reagent in extra pure acetone (Merck). The nonionic surfactant, Triton X-114 (Fluka, Chemie AG, Switzerland) was used without further purification. 1.25 g of Triton X-114 was dissolved in 50 ml of distilled water to give a 2.5% (w/v) of surfactant solution. The desirable pH (pH 6) was adjusted by dissolving appropriate amounts of sodium acetate in water (0.0125 mol l−1 ) and adding nitric acid (Merck) and sodium hydroxide (Merck) solutions. 2.2. Apparatus Simultaneous inductively coupled plasma optical emission spectrometry (ICP-OES, Varian Vista-PRO, Australia) coupled to a V-groove nebulizer and equipped with a charge coupled device (CCD) detector was used for simultaneous measurements of Zr and Hf in the surfactant-rich phase. The argon gas with 99.999% purity for ICP-OES was purchased from Roham Gas Company (Tehran, Iran). A thermostated bath (GFL model D 3006 Burgwedel) maintained at the desired temperature was used for cloud point extraction experiments and a MSE (Mistral 3000i, England) centrifuge was utilized to accelerate the phase separation process. 2.3. Procedure For the cloud point extraction, aliquots of solution containing the analytes, quinalizarine (3.4 × 10−5 mol l−1 ) and Triton X-114 (0.1%, w/v) were adjusted to the appropriate pH value (pH 6). These mixtures were kept in the thermostatic bath at 55 ◦ C (the temperature above the cloud point temperature of system) for 7 min. Since Triton X-114 is denser than water, the surfactant-rich phase typically settles through the aqueous phase. In order to accelerate the phase separation, the turbid solutions were centrifuged for 7.5 min at 3500 rpm. After that, the tubes were cooled in an ice bath for 5 min to reach a denser surfactant-rich phase that could facilitate the separation of aqueous phase by means of pipette. After the phase separation, 1.2 ml of 1-propanol (30%, v/v, in water) containing 1 mol l−1 HNO3 was added to the surfactant-rich phase
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Fig. 1. Experimental schemes of zirconium and hafnium pre-concentration by CPE method. Table 1 The optimized conditions for ICP determination of Zr and Hf ions ICP-OES conditions (radial torch) RF generator power (kW) Frequency of RF generator (MHz) Plasma gas flow rate (l min−1 ) Auxiliary gas flow rate (l min−1 ) Nebulizer pressure (kPa)
1.65 40 12.0 0.75 240
Hf wavelength (nm) Zr wavelength (nm) Viewing height (mm) Pump rate (rpm)
282.023 343.823 9 15
to reduce its viscosity and increase the sample volume for the ICP-OES measurement. Finally, the samples were introduced into the plasma with a peristaltic pump. The intensity was measured at the proper wavelength for each analyte, 282.023 and 343.823 nm for Hf and Zr, respectively. Fig. 1 shows schematically the overall CPE procedure. All optimizing experiments were done using Falcon tubes with 10 ml volume and in the case of calibration graphs and real samples for increasing the enrichment factors; Falcon tubes with 50 ml volumes were applied. 3. Results and discussion
Fig. 2. Effect of reagent concentration on the extraction of Zr and Hf complexes. Extraction conditions: 1 mg l−1 Hf, 0.1 mg l−1 Zr, 0.1% (w/v) Triton X-114, equilibration temperature 50 ◦ C (for 10 min) and centrifugation time 10 min.
3.1. Method development Before proceeding with the analysis of standards and real samples, an optimization study was needed to ensure that the maximum extraction is attained. Different parameters influencing the intensity of optical emission signals of analytes in ICP-OES instrument, such as radio frequency (RF), generator power, viewing height, plasma and auxiliary gas flow rates and nebulizer pressure were optimized. Then, parameters affecting the proposed reactions and cloud point extraction efficiency, including surfactant and chelating agent concentrations, equilibrium time, temperature, pH of solution and centrifuge time, were considered and optimized by the univariate optimization approach to estimate the importance of each factor in the extraction efficiency. The optimized conditions of ICP-OES are summarized in Table 1. 3.2. Effect of reagent concentration The reagent concentration was the first parameter studied for its effect on the extraction of Zr and Hf. The variation of
emission intensities with reagent concentration in the range of 0–2 × 10−4 mol l−1 is shown in Fig. 2. The results revealed that at the reagent concentration of 3.4 × 10−5 mol l−1 , more extraction occurred. This value was, therefore, selected as the optimal chelating agent concentration value. However, using an excessive amount of reagent was found to decrease the extraction performance, because utilizing a higher concentration of quinalizarine causes more volume of acetone as solvent to enter the solution that can prevent the micelle formation and reduce the extraction efficiency. 3.3. Effect of surfactant concentration Triton X-114 was chosen for the extraction due to its low cloud point temperature (CPT) and high density of the surfactant-rich phase, which facilitate phase separation by centrifugation. A successful cloud point extraction should maximize the extraction efficiency as well as minimizing the phase volume ratio to improve the enrichment factors. The variation of extraction efficiency upon the surfactant concentration was
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Fig. 3. Effect of Triton X-114 on the extraction of Zr and Hf complexes. Extraction conditions: 1 mg l−1 Hf, 0.1 mg l−1 Zr, 3.4 × 10−5 mol l−1 quinalizarine, equilibration temperature 50 ◦ C (for 10 min) and centrifugation time 10 min.
studied within the range 0.01–1% (w/v) of Triton X-114. The differences observed in the signals at various surfactant concentrations are shown in Fig. 3. As can be seen, the quantitative extraction was observed at Triton X-114 concentration of 0.1% (w/v). At lower concentrations of surfactant, the extraction efficiency is low probably due to the inadequacy of the assemblies to entrap the hydrophobic complex quantitatively [33]. At Triton X-114 concentrations higher than 0.1% (w/v), the decrease in the magnitude of the emission signals can be explained by increasing the volume of the surfactant-rich phase. Therefore, in order to achieve a good enrichment factors and high extraction efficiency, Triton X-114 concentration of 0.1% (w/v) was chosen. In this condition, it was shown that the recovery of the analytes using a single step extraction was quantitative. 3.4. Effect of pH and ionic strength The extraction of metal ions by the cloud point method involves prior formation of a hydrophobic complex that extracted into a small volume of surfactant-rich phase, thus obtaining the desired pre-concentration. The extraction yield depends on the pH at which the complex formation occurs. The effect of pH upon the complex formation of Zr and Hf was studied within the pH range of 2–10 using sodium acetate solution by addition of NaOH or HNO3 . The results illustrated in Fig. 4 reveal that for both Zr and Hf, the emission intensities are nearly constant in the pH range of 3–7. Hence, the pH of 6.0 was chosen for further extractions. The salt effect was studied by the addition of NaCl to the solution in the range of 0–2 mol l−1 . The results have shown that the addition of the salt has no significant effect on the extraction efficiency. This is in agreement with the literature results, which demonstrate that an increase in ionic strength in micellar systems does not seriously alter the extraction efficiency of the analytes [34].
Fig. 4. Effect of pH on the extraction of Zr and Hf complexes. Extraction conditions: 1 mg l−1 Hf, 0.1 mg l−1 Zr, 3.4 × 10−5 mol l−1 quinalizarine, 0.1% (w/v) Triton X-114, equilibration temperature 50 ◦ C (for 10 min) and centrifugation time 10 min.
Fig. 5. Effect of equilibration time on the extraction of Zr and Hf complexes. Extraction conditions: 1 mg l−1 Hf, 0.1 mg l−1 Zr, 3.4 × 10−5 mol l−1 quinalizarine, 0.1% (w/v) Triton X-114, pH 6 (acetic acid/acetate buffer) equilibration temperature 55 ◦ C and centrifugation time 10 min.
employ the shortest equilibration time and the lowest equilibration temperature possible, which compromise the complexation of reaction and efficient separation of phases. It appears that the phase volume ratio of all non-ionic surfactants decreases as the equilibration temperature increases. The greatest analyte enrichment factors are, thus, expected to be under conditions where the CPE is conducted using equilibration temperatures that are well above the CPT of the surfactant [33]. The temperature at which phase separation occurs is a function of the surfactant concentration and can be altered (either increased or decreased) in the presence of other materials (i.e. salts, alcohols, non-ionic surfactants and some organic compounds). It was found that the temperature of 55 ◦ C is adequate for the extraction of both analytes. The dependence of the extraction efficiency upon the equilibration time was studied in the range of 0–20 min. The results are shown in Fig. 5. Accordingly, an equilibration time of 7 min was chosen as the best to obtain the quantitative extraction. 3.6. Effect of centrifugation time
3.5. Influence of equilibrium time and temperature The equilibrium temperature above the CPT and the incubation time were the parameters considered next. It is desirable to
The centrifugation time does not have a considerable effect on the analytical characteristics of the CPE method. This parameter was examined in the range of 2–15 min at 3500 rpm.
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A time of 7.5 min was selected as optimum, since complete phase separation occurs in this time and no appreciable improvements were observed for larger times. 3.7. Influence of the surfactant-rich phase viscosity In the phase separation step, the surfactant-rich phase with high viscosity was settled. The addition of a diluent, such as 30% (v/v) of propanol/1 M HNO3 reduces the surfactant phase viscosity and facilitates its transfer into the ICP nebulizer. Therefore, 1.2 ml of diluent was chosen as the optimized value and added to the surfactant-rich phase in order to ensure a sufficient volume of the sample for aspiration. The final surfactant-rich phase volume was 1.35 ml. The optimized conditions of CPE are summarized in Table 2. 3.8. Figures of merit Calibration graphs were obtained using 50 ml of standard solutions buffered at pH 6 and containing 0.1% (w/v) Triton X-114. For this purpose, standard solutions containing Zr and Hf ions in the range of 0.5–1000 µg l−1 were examined by the proposed procedure and it was observed that calibration curves were linear in this range. Analytical characteristics of the proposed procedure are presented in Table 3. The relative standard deviations (RSD) resulting from the analysis of 8 replicates of 50 ml solution containing 200 µg l−1 Zr and Hf were 2.9 and 2.6%, respectively. The detection limits were calculated as the concentration equivalent to three times the standard deviation of the blank divided into the slope of calibration curve were 0.26 and 0.31 µg l−1 for Zr and Hf, respectively. The enrichment factors were calculated as the ratio of slope of pre-concentrated samples to that obtained without pre-concentration. According to this concept, the enrichment factors of 38.9 and 35.8 were obtained for Zr and Hf, respectively.
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3.9. Interferences Due to high selectivity provided by inductively coupled plasma spectrometry, the only interferences investigated were cations that may form complexes with quinalizarine, and thus decrease the extraction efficiency. After selecting the optimum conditions, the possible interfering effects of ions were studied at three different metal to interfering ion ratios of 1:1000, 1:900 and 1:750 while the analytes’ concentrations were set at 200 µg l−1 . Triton X-114 and quinalizarine concentrations were adjusted at 0.1 % (w/v) and 3.4 × 10−5 mol l−1 , respectively. According to Table 4, in most cases except Mn2+ and Fe3+ , and at the concentration levels of foreign ions which were studied, no significant interference was observed and it was proved that Zr and Hf recoveries were quantitative. Mn2+ and Fe3+ interfere quite significantly at the higher interference ratios (weight ratio of interfering ion/Zr = 1000) but when the ratios were lowered to 750 and 900 for Mn2+ and Fe3+ , respectively, the interference effect was eliminated. Moreover, it was shown that presence of alkaline metals and anions such as nitrate, sulfate, chloride and fluoride did not have any adverse effects on the extraction efficiency. It is worthy to note that interferences by foreign cations may affect the reagent concentration; therefore, any reagent loss should be avoided by increasing the reagent concentration. 3.10. Determination of Zr and Hf in real samples Finally, the applicability and reliability of this pre-concentration method for the analysis of Zr and Hf was investigated in water and alloy samples. First, each water sample was extracted at optimal conditions by proposed procedure and it was shown that the concentration of Zr and Hf was lower than the limit of detection of our method. Then, for studying the matrix effect on the extraction efficiency, the water solutions were spiked at 20 µg l−1 concentration level of Zr and Hf. The summarized results in Table 5 are the average of three replicate measurements. The results of sea water samples were signifi-
Table 2 The optimized conditions for Zr and Hf determination using CPE method Optimum CPE conditions Chelating agent (mol l−1 )
3.4 × 10−5
Surfactant percent (%, w/v) Buffer acetic
0.1 Acetic acid/acetate (0.0125 M, pH 6)
Equilibrium temperature (◦ C) Centrifuge time (min) Equilibrium time (min) Diluent 30% (w/v) propanol/1 mol l−1 HNO3
55 7.5 7
Table 3 Analytical characteristics of CPE method Parameter
Hf
Zr
Wavelength (nm) Limit of detection (µg l−1 ) %RSD (n = 8, C = 200 µg l−1 ) Regression equation Correlation coefficient Enrichment factors
282.023 0.31 2.6 I = 91.68C (µg l−1 ) − 933.54 0.9960 35.8
343.823 0.26 2.9 I = 533.44C (µg l−1 ) − 3235.7 0.9971 38.9
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Table 4 Effects of the foreign ions on the recovery of 200 µg l−1 of Zr and Hf from aqueous solutions Ions Alkaline-earth metals Cd2+ Co2+ Ag+ Hg2+ Cr3+ La3+
Mn2+ Cu2+ Ni2+ Zn2+ Pb2+ Al3+ Fe3+ Fe2+
Concentration (mg l−1 )
Ion/Zr or Hf ratio (w/w)
Recovery (%) Hf
Zr
200 200 200 200 200 200 200 180 150 200 150 200 200 200 200 200 200 200
1000 1000 1000 1000 1000 1000 1000 900 750 1000 750 1000 1000 1000 1000 1000 1000 1000
95.1 97.4 102.7 102.4 95.4 100.0 96.5 96.0 96.1 50.2 97.4 99.0 100.7 95.8 90.2 97.0 77.4 102.1
97.4 99.2 98.6 96.7 97.0 96.8 88.4 96.1 99.2 65.1 97.9 95.0 97.0 94.0 91.0 96.6 75.0 101.7
Table 5 Determination of Zr and Hf in 20 µg l−1 spiked water samples Found (µg l−1 )a
Real samples Caspian sea water Caspian sea waterb Well water Tap water Spring water
Extraction efficiency (%)
Hf (IV)
Zr (IV)
Hf (IV)
Zr (IV)
12.17 ± 0.65 19.00 ± 1.61 19.53 ± 0.58 19.53 ± 0.32 19.90 ± 1.30
15.71 ± 0.81 19.20 ± 1.10 19.79 ± 1.29 19.80 ± 0.36 19.94 ± 0.75
60.9 95.0 97.7 97.7 99.5
78.6 96.0 99.0 99.0 99.8
a Mean of three replicate measurements ± standard deviation. b Sea water sample after standard addition method.
Table 6 Determination of Zr and Hf in certified sample of alloy Sample
Certified (mg kg−1 )
Found (mg kg−1 )a
Hf
Zr
Hf
Zr
Hf
Zr
Cu alloy
29.85
417.20
28.78 ± 1.90
404.60 ± 13.38
96.4
97.0
Extraction efficiency (%)
a Mean of three replicate measurements ± standard deviation.
cantly different from the spiked amounts probably due to high ionic strength of sea water that affects the extraction efficiency. Therefore, to compensate the matrix effect, sea water samples were examined by the standard addition method. For a sample containing 20 µg l−1 of Zr and Hf, values of 19.00 µg l−1 for Hf and 19.20 µg l−1 for Zr were obtained by the standard addition method and an improvement in accuracy was achieved. For determination of Zr and Hf in alloy, the alloy sample was weighted and dissolved in 3:1 HCl/HNO3 . A definite volume of this solution was extracted using the proposed method at optimal conditions. The results are shown in Table 6. According to the results of Tables 5 and 6, the good agreement between these results and the known values indicates the successful applicability of this method for simultaneous determination of Zr and Hf in real samples.
4. Conclusion
The use of micellar systems as an alternative to other techniques of separation and pre-concentration offers several advantages including experimental convenience, safety, and being a rapid and inexpensive method. In this study, we proposed the use of the cloud point extraction for the pre-concentration of Zr and Hf cations as a prior step to their determination by ICPOES. This method gives a very low limit of detection and good RSD for both the analytes. The method was verified with real samples and it was proven satisfactory for the simultaneous determination of trace levels of Zr and Hf in a variety of water matrixes. Also, it is possible to obtain a better limit of detection by extraction of Zr and Hf from large volumes of sample solu-
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tion and diluting the surfactant-rich phase to a smaller volume, or using the flow injection method. References [1] P. Peralta-Zamora, J.W. Martins, Talanta 49 (1999) 937. [2] M.A. Kabili, M.A. Aki, A.M. Abdallah, D.S. Ismail, Anal. Sci. 16 (2000) 713. [3] A. Abbaspour, L. Baramakeh, Anal. Sci. 18 (2002) 1127. [4] S. Oszwaldowski, R. Lipka, M. Jarosz, Anal. Chim. Acta 361 (1998) 177. [5] S. Lin, C. Peng, J. Anal. At. Spectrom. 5 (1990) 509. [6] B.A. Mckelvey, K.J. Orians, Geochim. Cosmochim. Acta 57 (1993) 3801. [7] D.V. Vivit, B.S.W. King, Geostand. Newslett. 12 (1988) 363. [8] S.J.J. Tsai, H.T. Yan, Analyst 118 (1993) 521. [9] R. Purohit, S. Devi, Talanta 44 (1997) 319. [10] A. Hulanicki, J. Surgiewicz, I. Jaron, Talanta 44 (1997) 1159. [11] N. Lihareva, M. Delaloye, Fresenius J. Anal. Chem. 357 (1997) 314. [12] G.E.M. Hall, J.C. Pelchat, J. Loop, J. Anal. At. Spectrom. 5 (1990) 339. [13] B. Gorski, S.A. Karamian, Y.T. Oganessian, S.L. Bogomolov, J. Radioanal. Nucl. Chem. 170 (1993) 353. [14] P. Peralata-Zamora, L. Cornejo-Ponce, M.I. Maretti, S. Bueno, J.W. Martins, Talanta 44 (1997) 811. [15] M.D. Palmieri, J.S. Fritz, Anal. Chem. 59 (1987) 2226. [16] S. Oszwaldowski, J. Jakubowska, Talanta 60 (2003) 643. [17] X.J. Yang, C. Pin, Anal. Chim. Acta 458 (2002) 375.
425
[18] T.C. Duan, H.T. Chen, X.J. Zeng, J. Anal. At. Spectrom. 17 (2002) 410. [19] Z.P. Wang, L.L. Shi, G.S. Chen, K.L. Cheng, Talanta 51 (2000) 315. [20] W.L. Hinze, CRC Crit. Rev. Anal. Chem. 24 (1993) 133. [21] H. Tani, T. Kamidate, H. Watanabe, J. Chromatogr. A 780 (1997) 229. [22] C.D. Stalikas, Trends Anal. Chem. 21 (2002) 343. [23] Z.S. Ferrera, C.P. Sanz, C.M. Santana, J.J.S. Rodriguez, Trends Anal. Chem. 23 (2004) 469. [24] F.H. Quina, W.L. Hinze, Ind. Eng. Chem. Res. 38 (1999) 4150. [25] J.C.A. de Wuilloud, R.G. Wuilloud, M.F. Silva, R.A. Olsina, L.D. Martinez, Spectrochim. Acta Part B 57 (2002) 365. [26] J. Chen, K. Chuan Teo, Anal. Chim. Acta 434 (2001) 325. [27] M.C.C. Oliveros, O.J. de Blas, J.L.P. Paron, B.M. Cordero, J. Anal. At. Spectrom. 13 (1998) 547. [28] B. Lindman, H. Wennerstrom, J. Phys. Chem. 95 (1991) 6053. [29] M. Corti, V. DeGiorgio, J.B. Hayter, M. Zulanf, Chem. Phys. Lett. 109 (1984) 579. [30] V. DeGiorgio, R. Piazza, M. Corti, C. Minero, J. Chem. Phys. 82 (1984) 1025. [31] P. Nilsson, H. Wennerstrom, B. Lindman, J. Phys. Chem. 87 (1983) 1377. [32] R. Carabias-Martinez, E. Rodriguez-Gonzalo, B. Moreno-Cordero, J.L. Perez-Pavon, C. Garcia-Pinto, E. Fernandez Laespada, J. Chromatogr. A 902 (2000) 251. [33] A. Safavi, H. Abdollahi, M.R. Hormozi Nezhad, R. Kamali, Spectrochim. Acta Part A 60 (2004) 2897. [34] M.J. Schich (Ed.), Non-Ionic Surfactants, Dekker, New York, 1987.
Cloud point extraction and simultaneous determination of zirconium and hafnium using ICP-OES Shahab Shariati, Yadollah Yamini ∗ Department of Chemistry, Faculty of Sciences, Tarbiat Modarres University, P.O. Box 14115-175, Tehran, Iran Received 22 September 2005; accepted 1 December 2005 Available online 9 January 2006
Abstract In the present study a simple versatile separation method using cloud point procedure for extraction of trace levels of zirconium and hafnium is proposed. The extraction of analytes from aqueous samples was performed in the presence of quinalizarine as chelating agent and Triton X-114 as a non-ionic surfactant. After phase separation, the surfactant-rich phase was diluted with 30% (v/v) propanol solution containing 1 mol l−1 HNO3 . Then, the enriched analytes in the surfactant-rich phase were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The different variables affecting the complexation and extraction conditions were optimized. Under the optimum conditions (i.e. 3.4 × 10−5 mol l−1 quinalizarine, 0.1% (w/v) Triton X-114, 55 ◦ C equilibrium temperature) the calibration graphs were linear in the range of 0.5–1000 µg l−1 with detection limits (DLs) of 0.26 and 0.31 µg l−1 for Zr and Hf, respectively. Under the presence of foreign ions no significant interference was observed. The precision (%RSD) for 8 replicate determinations at 200 µg l−1 of Zr and Hf was better than 2.9% and the enrichment factors were obtained as 38.9 and 35.8 for Zr and Hf, respectively. Finally, the proposed method was successfully utilized for the determination of these cations in water and alloy samples. © 2005 Elsevier Inc. All rights reserved. Keywords: Cloud point extraction; Zirconium; Hafnium; Quinalizarine; Triton X-114
1. Introduction Zirconium (Zr) and hafnium (Hf) are strategic elements and their identification and determination are very important. Zr is used for removing sulfur, nitrogen and oxygen from steel and in the copper manufacturing. Its alloys are employed in the production of optical glasses with high refractive index and in the ceramic industry to produce enamels. Also its transparency to thermal neutrons has made Zr a good structural material in nuclear reactors and chemical plants. Hafnium is found combined in natural zirconium compounds but does not exist as a free element in nature. Minerals that contain zirconium, such as alvite [(Hf, Th, Zr)SiO4 ·H2 O], thortveitite and zircon (ZrSiO4 ), usually contain between 1 and 5% hafnium. It has been found to be a good absorber of neu* Corresponding author. Fax: +98 21 88006544.
E-mail address: [email protected] (Y. Yamini). 0021-9797/$ – see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.12.005
trons, leading to its use as a moderator in control rods for nuclear reactors. It is also used in the manufacture of the filaments for electric light bulbs. Due to lanthanide contraction, Zr and Hf are similar in chemistry and exist together in nature [1–3]. The determination of very low concentrations of Zr and Hf usually requires separation and pre-concentration steps. The methods for separation of these elements are based on tiny differences in stabilities of metal complexes. In order to determine Zr, different spectroanalytical techniques were used [4]: Laser ablation inductively coupled plasma optical emission spectrometry LAICP-OES [5], inductively coupled plasma mass spectrometry ICP-MS [6], X-ray fluorescence [7], also one-step procedures such as reversedphase liquid chromatographic separation (RP-LC) [8] or chelating ion exchange followed by spectrophotometric detection [9] have been reported. The detection limits of the above methods for determination of Zr varied in the range of 0.1–3 mg l−1 .
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Similarly, Hf was determined by ICP-OES [10,11], ICPMS [12] and neutron activation analysis [13] methods. The detection limits of all methods mentioned above were in the range of 2–30 µg l−1 . Also, the simultaneous determination of these two elements was carried out by energy dispersive X-ray fluorescence after solid phase pre-concentration [14], liquid chromatography separation and determination of their hydroxamic acid chelates [15], ternary complexes of them with 2(5-bromo-2-pyridylazo)-5-diethylamino phenol (5-Br-PADAP) and fluoride without extraction [4] and after solid phase extraction [16], also separation using N -benzoyl-N -phenyl hydroxyl amine (BPHA) supported on a microporous polymeric resin [17], coprecipitation with Ti(OH)4 –Fe(OH)3 [18] followed by ICP-OES determination and the spectrophotometric method assisted by chemometric procedures have been proposed [19]. Separations and pre-concentrations based on the cloud point extraction (CPE) are becoming an important and practical application of using surfactants in analytical chemistry. The CPE has been used successfully for the pre-concentration of species of widely differing character and nature, such as metal ions, proteins and other biomaterials or organic compounds of strongly differing polarity. In this method, any component originally present in the solution that interacts with the micellar aggregate either directly (generally hydrophobic organic compounds) or after a previous derivatization reaction (i.e. metal ions after reaction with a suitable hydrophobic ligand) can thus be extracted differently, (depending on the micelle–solute binding interactions) from the initial solution and concentrated in the small volume of the surfactant-rich phase. The small volume of the surfactant-rich phase obtained with this method (generally between 100 and 400 µl) permits the design of extraction schemes that are simple, cheap, efficient and safe in comparison with liquid–liquid extraction methods [20–27]. The mechanism by which separation occurs is poorly understood. Some authors have proposed that it would be due to an increase in the micellar aggregation number when temperature is increased [28,29]. Others have suggested that the phase separation mechanism would be caused by a change in micellar interactions, which are repulsive at low temperatures but predominantly attractive at high temperatures [30]. Other authors have explained the cloud point phenomenon on the basis of the dehydration process that occurs in the external layer of the micelles of non-ionic surfactants when temperature is increased [31]. Also, dielectric constant of water decreases by increasing temperature, rendering it to a poorer solvent for the hydrophobic portion of the surfactant molecule [32]. In the present work, the cloud point extraction has been developed and optimized for the extraction and pre-concentration of Zr(IV) and Hf(IV) in water samples. For this purpose, Zr(IV) and Hf(IV) form chelates with quinalizarine and resultant complexes pre-concentrate using octyl phenoxypolyethoxy ethanol (Triton X-114) as a non-ionic surfactant. Finally, simultaneous determinations of these elements were performed by ICPOES and the proposed method was applied to the real samples.
2. Experimental 2.1. Reagents and materials All chemicals used were of analytical reagent grade. Zr stock solution (1000 mg l−1 ) was prepared by the direct dissolution of ZrOCl2 ·8H2 O (99.5%) in double distilled water. The stock solution of Hf (1000 mg l−1 ) was purchased from Merck (Darmstadt, Germany). These standard solutions were diluted with distilled water to prepare mixed stock solutions in such a way that the concentration of the mixtures was 10 and 100 mg l−1 inspect of Zr and Hf, respectively. All required solutions were freshly prepared by diluting the mixed standard solution with buffer solution to the required concentration after the addition of ligand and surfactant. Reagent grade 1,2,5,8-tetrahydroxyanthraquinone (quinalizarine) from Merck was used as chelating agent. The standard solution of quinalizarine (10−3 mol l−1 ) was prepared by dissolving proper amounts of reagent in extra pure acetone (Merck). The nonionic surfactant, Triton X-114 (Fluka, Chemie AG, Switzerland) was used without further purification. 1.25 g of Triton X-114 was dissolved in 50 ml of distilled water to give a 2.5% (w/v) of surfactant solution. The desirable pH (pH 6) was adjusted by dissolving appropriate amounts of sodium acetate in water (0.0125 mol l−1 ) and adding nitric acid (Merck) and sodium hydroxide (Merck) solutions. 2.2. Apparatus Simultaneous inductively coupled plasma optical emission spectrometry (ICP-OES, Varian Vista-PRO, Australia) coupled to a V-groove nebulizer and equipped with a charge coupled device (CCD) detector was used for simultaneous measurements of Zr and Hf in the surfactant-rich phase. The argon gas with 99.999% purity for ICP-OES was purchased from Roham Gas Company (Tehran, Iran). A thermostated bath (GFL model D 3006 Burgwedel) maintained at the desired temperature was used for cloud point extraction experiments and a MSE (Mistral 3000i, England) centrifuge was utilized to accelerate the phase separation process. 2.3. Procedure For the cloud point extraction, aliquots of solution containing the analytes, quinalizarine (3.4 × 10−5 mol l−1 ) and Triton X-114 (0.1%, w/v) were adjusted to the appropriate pH value (pH 6). These mixtures were kept in the thermostatic bath at 55 ◦ C (the temperature above the cloud point temperature of system) for 7 min. Since Triton X-114 is denser than water, the surfactant-rich phase typically settles through the aqueous phase. In order to accelerate the phase separation, the turbid solutions were centrifuged for 7.5 min at 3500 rpm. After that, the tubes were cooled in an ice bath for 5 min to reach a denser surfactant-rich phase that could facilitate the separation of aqueous phase by means of pipette. After the phase separation, 1.2 ml of 1-propanol (30%, v/v, in water) containing 1 mol l−1 HNO3 was added to the surfactant-rich phase
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Fig. 1. Experimental schemes of zirconium and hafnium pre-concentration by CPE method. Table 1 The optimized conditions for ICP determination of Zr and Hf ions ICP-OES conditions (radial torch) RF generator power (kW) Frequency of RF generator (MHz) Plasma gas flow rate (l min−1 ) Auxiliary gas flow rate (l min−1 ) Nebulizer pressure (kPa)
1.65 40 12.0 0.75 240
Hf wavelength (nm) Zr wavelength (nm) Viewing height (mm) Pump rate (rpm)
282.023 343.823 9 15
to reduce its viscosity and increase the sample volume for the ICP-OES measurement. Finally, the samples were introduced into the plasma with a peristaltic pump. The intensity was measured at the proper wavelength for each analyte, 282.023 and 343.823 nm for Hf and Zr, respectively. Fig. 1 shows schematically the overall CPE procedure. All optimizing experiments were done using Falcon tubes with 10 ml volume and in the case of calibration graphs and real samples for increasing the enrichment factors; Falcon tubes with 50 ml volumes were applied. 3. Results and discussion
Fig. 2. Effect of reagent concentration on the extraction of Zr and Hf complexes. Extraction conditions: 1 mg l−1 Hf, 0.1 mg l−1 Zr, 0.1% (w/v) Triton X-114, equilibration temperature 50 ◦ C (for 10 min) and centrifugation time 10 min.
3.1. Method development Before proceeding with the analysis of standards and real samples, an optimization study was needed to ensure that the maximum extraction is attained. Different parameters influencing the intensity of optical emission signals of analytes in ICP-OES instrument, such as radio frequency (RF), generator power, viewing height, plasma and auxiliary gas flow rates and nebulizer pressure were optimized. Then, parameters affecting the proposed reactions and cloud point extraction efficiency, including surfactant and chelating agent concentrations, equilibrium time, temperature, pH of solution and centrifuge time, were considered and optimized by the univariate optimization approach to estimate the importance of each factor in the extraction efficiency. The optimized conditions of ICP-OES are summarized in Table 1. 3.2. Effect of reagent concentration The reagent concentration was the first parameter studied for its effect on the extraction of Zr and Hf. The variation of
emission intensities with reagent concentration in the range of 0–2 × 10−4 mol l−1 is shown in Fig. 2. The results revealed that at the reagent concentration of 3.4 × 10−5 mol l−1 , more extraction occurred. This value was, therefore, selected as the optimal chelating agent concentration value. However, using an excessive amount of reagent was found to decrease the extraction performance, because utilizing a higher concentration of quinalizarine causes more volume of acetone as solvent to enter the solution that can prevent the micelle formation and reduce the extraction efficiency. 3.3. Effect of surfactant concentration Triton X-114 was chosen for the extraction due to its low cloud point temperature (CPT) and high density of the surfactant-rich phase, which facilitate phase separation by centrifugation. A successful cloud point extraction should maximize the extraction efficiency as well as minimizing the phase volume ratio to improve the enrichment factors. The variation of extraction efficiency upon the surfactant concentration was
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Fig. 3. Effect of Triton X-114 on the extraction of Zr and Hf complexes. Extraction conditions: 1 mg l−1 Hf, 0.1 mg l−1 Zr, 3.4 × 10−5 mol l−1 quinalizarine, equilibration temperature 50 ◦ C (for 10 min) and centrifugation time 10 min.
studied within the range 0.01–1% (w/v) of Triton X-114. The differences observed in the signals at various surfactant concentrations are shown in Fig. 3. As can be seen, the quantitative extraction was observed at Triton X-114 concentration of 0.1% (w/v). At lower concentrations of surfactant, the extraction efficiency is low probably due to the inadequacy of the assemblies to entrap the hydrophobic complex quantitatively [33]. At Triton X-114 concentrations higher than 0.1% (w/v), the decrease in the magnitude of the emission signals can be explained by increasing the volume of the surfactant-rich phase. Therefore, in order to achieve a good enrichment factors and high extraction efficiency, Triton X-114 concentration of 0.1% (w/v) was chosen. In this condition, it was shown that the recovery of the analytes using a single step extraction was quantitative. 3.4. Effect of pH and ionic strength The extraction of metal ions by the cloud point method involves prior formation of a hydrophobic complex that extracted into a small volume of surfactant-rich phase, thus obtaining the desired pre-concentration. The extraction yield depends on the pH at which the complex formation occurs. The effect of pH upon the complex formation of Zr and Hf was studied within the pH range of 2–10 using sodium acetate solution by addition of NaOH or HNO3 . The results illustrated in Fig. 4 reveal that for both Zr and Hf, the emission intensities are nearly constant in the pH range of 3–7. Hence, the pH of 6.0 was chosen for further extractions. The salt effect was studied by the addition of NaCl to the solution in the range of 0–2 mol l−1 . The results have shown that the addition of the salt has no significant effect on the extraction efficiency. This is in agreement with the literature results, which demonstrate that an increase in ionic strength in micellar systems does not seriously alter the extraction efficiency of the analytes [34].
Fig. 4. Effect of pH on the extraction of Zr and Hf complexes. Extraction conditions: 1 mg l−1 Hf, 0.1 mg l−1 Zr, 3.4 × 10−5 mol l−1 quinalizarine, 0.1% (w/v) Triton X-114, equilibration temperature 50 ◦ C (for 10 min) and centrifugation time 10 min.
Fig. 5. Effect of equilibration time on the extraction of Zr and Hf complexes. Extraction conditions: 1 mg l−1 Hf, 0.1 mg l−1 Zr, 3.4 × 10−5 mol l−1 quinalizarine, 0.1% (w/v) Triton X-114, pH 6 (acetic acid/acetate buffer) equilibration temperature 55 ◦ C and centrifugation time 10 min.
employ the shortest equilibration time and the lowest equilibration temperature possible, which compromise the complexation of reaction and efficient separation of phases. It appears that the phase volume ratio of all non-ionic surfactants decreases as the equilibration temperature increases. The greatest analyte enrichment factors are, thus, expected to be under conditions where the CPE is conducted using equilibration temperatures that are well above the CPT of the surfactant [33]. The temperature at which phase separation occurs is a function of the surfactant concentration and can be altered (either increased or decreased) in the presence of other materials (i.e. salts, alcohols, non-ionic surfactants and some organic compounds). It was found that the temperature of 55 ◦ C is adequate for the extraction of both analytes. The dependence of the extraction efficiency upon the equilibration time was studied in the range of 0–20 min. The results are shown in Fig. 5. Accordingly, an equilibration time of 7 min was chosen as the best to obtain the quantitative extraction. 3.6. Effect of centrifugation time
3.5. Influence of equilibrium time and temperature The equilibrium temperature above the CPT and the incubation time were the parameters considered next. It is desirable to
The centrifugation time does not have a considerable effect on the analytical characteristics of the CPE method. This parameter was examined in the range of 2–15 min at 3500 rpm.
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A time of 7.5 min was selected as optimum, since complete phase separation occurs in this time and no appreciable improvements were observed for larger times. 3.7. Influence of the surfactant-rich phase viscosity In the phase separation step, the surfactant-rich phase with high viscosity was settled. The addition of a diluent, such as 30% (v/v) of propanol/1 M HNO3 reduces the surfactant phase viscosity and facilitates its transfer into the ICP nebulizer. Therefore, 1.2 ml of diluent was chosen as the optimized value and added to the surfactant-rich phase in order to ensure a sufficient volume of the sample for aspiration. The final surfactant-rich phase volume was 1.35 ml. The optimized conditions of CPE are summarized in Table 2. 3.8. Figures of merit Calibration graphs were obtained using 50 ml of standard solutions buffered at pH 6 and containing 0.1% (w/v) Triton X-114. For this purpose, standard solutions containing Zr and Hf ions in the range of 0.5–1000 µg l−1 were examined by the proposed procedure and it was observed that calibration curves were linear in this range. Analytical characteristics of the proposed procedure are presented in Table 3. The relative standard deviations (RSD) resulting from the analysis of 8 replicates of 50 ml solution containing 200 µg l−1 Zr and Hf were 2.9 and 2.6%, respectively. The detection limits were calculated as the concentration equivalent to three times the standard deviation of the blank divided into the slope of calibration curve were 0.26 and 0.31 µg l−1 for Zr and Hf, respectively. The enrichment factors were calculated as the ratio of slope of pre-concentrated samples to that obtained without pre-concentration. According to this concept, the enrichment factors of 38.9 and 35.8 were obtained for Zr and Hf, respectively.
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3.9. Interferences Due to high selectivity provided by inductively coupled plasma spectrometry, the only interferences investigated were cations that may form complexes with quinalizarine, and thus decrease the extraction efficiency. After selecting the optimum conditions, the possible interfering effects of ions were studied at three different metal to interfering ion ratios of 1:1000, 1:900 and 1:750 while the analytes’ concentrations were set at 200 µg l−1 . Triton X-114 and quinalizarine concentrations were adjusted at 0.1 % (w/v) and 3.4 × 10−5 mol l−1 , respectively. According to Table 4, in most cases except Mn2+ and Fe3+ , and at the concentration levels of foreign ions which were studied, no significant interference was observed and it was proved that Zr and Hf recoveries were quantitative. Mn2+ and Fe3+ interfere quite significantly at the higher interference ratios (weight ratio of interfering ion/Zr = 1000) but when the ratios were lowered to 750 and 900 for Mn2+ and Fe3+ , respectively, the interference effect was eliminated. Moreover, it was shown that presence of alkaline metals and anions such as nitrate, sulfate, chloride and fluoride did not have any adverse effects on the extraction efficiency. It is worthy to note that interferences by foreign cations may affect the reagent concentration; therefore, any reagent loss should be avoided by increasing the reagent concentration. 3.10. Determination of Zr and Hf in real samples Finally, the applicability and reliability of this pre-concentration method for the analysis of Zr and Hf was investigated in water and alloy samples. First, each water sample was extracted at optimal conditions by proposed procedure and it was shown that the concentration of Zr and Hf was lower than the limit of detection of our method. Then, for studying the matrix effect on the extraction efficiency, the water solutions were spiked at 20 µg l−1 concentration level of Zr and Hf. The summarized results in Table 5 are the average of three replicate measurements. The results of sea water samples were signifi-
Table 2 The optimized conditions for Zr and Hf determination using CPE method Optimum CPE conditions Chelating agent (mol l−1 )
3.4 × 10−5
Surfactant percent (%, w/v) Buffer acetic
0.1 Acetic acid/acetate (0.0125 M, pH 6)
Equilibrium temperature (◦ C) Centrifuge time (min) Equilibrium time (min) Diluent 30% (w/v) propanol/1 mol l−1 HNO3
55 7.5 7
Table 3 Analytical characteristics of CPE method Parameter
Hf
Zr
Wavelength (nm) Limit of detection (µg l−1 ) %RSD (n = 8, C = 200 µg l−1 ) Regression equation Correlation coefficient Enrichment factors
282.023 0.31 2.6 I = 91.68C (µg l−1 ) − 933.54 0.9960 35.8
343.823 0.26 2.9 I = 533.44C (µg l−1 ) − 3235.7 0.9971 38.9
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Table 4 Effects of the foreign ions on the recovery of 200 µg l−1 of Zr and Hf from aqueous solutions Ions Alkaline-earth metals Cd2+ Co2+ Ag+ Hg2+ Cr3+ La3+
Mn2+ Cu2+ Ni2+ Zn2+ Pb2+ Al3+ Fe3+ Fe2+
Concentration (mg l−1 )
Ion/Zr or Hf ratio (w/w)
Recovery (%) Hf
Zr
200 200 200 200 200 200 200 180 150 200 150 200 200 200 200 200 200 200
1000 1000 1000 1000 1000 1000 1000 900 750 1000 750 1000 1000 1000 1000 1000 1000 1000
95.1 97.4 102.7 102.4 95.4 100.0 96.5 96.0 96.1 50.2 97.4 99.0 100.7 95.8 90.2 97.0 77.4 102.1
97.4 99.2 98.6 96.7 97.0 96.8 88.4 96.1 99.2 65.1 97.9 95.0 97.0 94.0 91.0 96.6 75.0 101.7
Table 5 Determination of Zr and Hf in 20 µg l−1 spiked water samples Found (µg l−1 )a
Real samples Caspian sea water Caspian sea waterb Well water Tap water Spring water
Extraction efficiency (%)
Hf (IV)
Zr (IV)
Hf (IV)
Zr (IV)
12.17 ± 0.65 19.00 ± 1.61 19.53 ± 0.58 19.53 ± 0.32 19.90 ± 1.30
15.71 ± 0.81 19.20 ± 1.10 19.79 ± 1.29 19.80 ± 0.36 19.94 ± 0.75
60.9 95.0 97.7 97.7 99.5
78.6 96.0 99.0 99.0 99.8
a Mean of three replicate measurements ± standard deviation. b Sea water sample after standard addition method.
Table 6 Determination of Zr and Hf in certified sample of alloy Sample
Certified (mg kg−1 )
Found (mg kg−1 )a
Hf
Zr
Hf
Zr
Hf
Zr
Cu alloy
29.85
417.20
28.78 ± 1.90
404.60 ± 13.38
96.4
97.0
Extraction efficiency (%)
a Mean of three replicate measurements ± standard deviation.
cantly different from the spiked amounts probably due to high ionic strength of sea water that affects the extraction efficiency. Therefore, to compensate the matrix effect, sea water samples were examined by the standard addition method. For a sample containing 20 µg l−1 of Zr and Hf, values of 19.00 µg l−1 for Hf and 19.20 µg l−1 for Zr were obtained by the standard addition method and an improvement in accuracy was achieved. For determination of Zr and Hf in alloy, the alloy sample was weighted and dissolved in 3:1 HCl/HNO3 . A definite volume of this solution was extracted using the proposed method at optimal conditions. The results are shown in Table 6. According to the results of Tables 5 and 6, the good agreement between these results and the known values indicates the successful applicability of this method for simultaneous determination of Zr and Hf in real samples.
4. Conclusion
The use of micellar systems as an alternative to other techniques of separation and pre-concentration offers several advantages including experimental convenience, safety, and being a rapid and inexpensive method. In this study, we proposed the use of the cloud point extraction for the pre-concentration of Zr and Hf cations as a prior step to their determination by ICPOES. This method gives a very low limit of detection and good RSD for both the analytes. The method was verified with real samples and it was proven satisfactory for the simultaneous determination of trace levels of Zr and Hf in a variety of water matrixes. Also, it is possible to obtain a better limit of detection by extraction of Zr and Hf from large volumes of sample solu-
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tion and diluting the surfactant-rich phase to a smaller volume, or using the flow injection method. References [1] P. Peralta-Zamora, J.W. Martins, Talanta 49 (1999) 937. [2] M.A. Kabili, M.A. Aki, A.M. Abdallah, D.S. Ismail, Anal. Sci. 16 (2000) 713. [3] A. Abbaspour, L. Baramakeh, Anal. Sci. 18 (2002) 1127. [4] S. Oszwaldowski, R. Lipka, M. Jarosz, Anal. Chim. Acta 361 (1998) 177. [5] S. Lin, C. Peng, J. Anal. At. Spectrom. 5 (1990) 509. [6] B.A. Mckelvey, K.J. Orians, Geochim. Cosmochim. Acta 57 (1993) 3801. [7] D.V. Vivit, B.S.W. King, Geostand. Newslett. 12 (1988) 363. [8] S.J.J. Tsai, H.T. Yan, Analyst 118 (1993) 521. [9] R. Purohit, S. Devi, Talanta 44 (1997) 319. [10] A. Hulanicki, J. Surgiewicz, I. Jaron, Talanta 44 (1997) 1159. [11] N. Lihareva, M. Delaloye, Fresenius J. Anal. Chem. 357 (1997) 314. [12] G.E.M. Hall, J.C. Pelchat, J. Loop, J. Anal. At. Spectrom. 5 (1990) 339. [13] B. Gorski, S.A. Karamian, Y.T. Oganessian, S.L. Bogomolov, J. Radioanal. Nucl. Chem. 170 (1993) 353. [14] P. Peralata-Zamora, L. Cornejo-Ponce, M.I. Maretti, S. Bueno, J.W. Martins, Talanta 44 (1997) 811. [15] M.D. Palmieri, J.S. Fritz, Anal. Chem. 59 (1987) 2226. [16] S. Oszwaldowski, J. Jakubowska, Talanta 60 (2003) 643. [17] X.J. Yang, C. Pin, Anal. Chim. Acta 458 (2002) 375.
425
[18] T.C. Duan, H.T. Chen, X.J. Zeng, J. Anal. At. Spectrom. 17 (2002) 410. [19] Z.P. Wang, L.L. Shi, G.S. Chen, K.L. Cheng, Talanta 51 (2000) 315. [20] W.L. Hinze, CRC Crit. Rev. Anal. Chem. 24 (1993) 133. [21] H. Tani, T. Kamidate, H. Watanabe, J. Chromatogr. A 780 (1997) 229. [22] C.D. Stalikas, Trends Anal. Chem. 21 (2002) 343. [23] Z.S. Ferrera, C.P. Sanz, C.M. Santana, J.J.S. Rodriguez, Trends Anal. Chem. 23 (2004) 469. [24] F.H. Quina, W.L. Hinze, Ind. Eng. Chem. Res. 38 (1999) 4150. [25] J.C.A. de Wuilloud, R.G. Wuilloud, M.F. Silva, R.A. Olsina, L.D. Martinez, Spectrochim. Acta Part B 57 (2002) 365. [26] J. Chen, K. Chuan Teo, Anal. Chim. Acta 434 (2001) 325. [27] M.C.C. Oliveros, O.J. de Blas, J.L.P. Paron, B.M. Cordero, J. Anal. At. Spectrom. 13 (1998) 547. [28] B. Lindman, H. Wennerstrom, J. Phys. Chem. 95 (1991) 6053. [29] M. Corti, V. DeGiorgio, J.B. Hayter, M. Zulanf, Chem. Phys. Lett. 109 (1984) 579. [30] V. DeGiorgio, R. Piazza, M. Corti, C. Minero, J. Chem. Phys. 82 (1984) 1025. [31] P. Nilsson, H. Wennerstrom, B. Lindman, J. Phys. Chem. 87 (1983) 1377. [32] R. Carabias-Martinez, E. Rodriguez-Gonzalo, B. Moreno-Cordero, J.L. Perez-Pavon, C. Garcia-Pinto, E. Fernandez Laespada, J. Chromatogr. A 902 (2000) 251. [33] A. Safavi, H. Abdollahi, M.R. Hormozi Nezhad, R. Kamali, Spectrochim. Acta Part A 60 (2004) 2897. [34] M.J. Schich (Ed.), Non-Ionic Surfactants, Dekker, New York, 1987.