Study on the optimal conditions to determine Cu, Pb and Cd using flame atomic absorption spectroscopy (F-AAS)

JOURNAL OF SCIENCE OF HNUE Natural Sci., 2008, Vol. 53, N ◦ . 5, pp. 89-94 STUDY ON THE OPTIMAL CONDITIONS TO DETERMINE Cu, Pb AND Cd USING FLAME ATOMIC ABSORPTION SPECTROSCOPY (F-AAS) Tran Cong Viet, Dao Thu Ha and Nguyen Quang Tuyen Hanoi National University of Education Abstract. In this study, optimal conditions for the determination of Cu, Pb, Cd were investigated by flame atomic absoroption spectroscopy (F-AAS). The content of Cu, Pb, Cd in domestic water selected in some lakes in Cau Giay and Tu Liem districts (Hanoi) were determined using the optimal conditions obtained above. 1. Introduction Due to the population explosion joining with industrialization and urbaniza- tion, it makes the living environment more polluted with every passing day and directly affects the lives of people, animals and plants. Therefore, for researchers, the study and the valuation of the heavy metal level in water are urgent duties. There are many methods for determination of heavy metals in which atomic absoroption spectrometry (F-AAS) is a promising method because it is very sensitive (order of ppm and ppp) and the usage is simple [1-5]. In this paper, the study on the optimal condition for determination of some heavy metals (such as Cu, Pb and Cd) in water in the Cau Giay and Tu Liem District using atomic absorption spectrometry have been informed. 2. Content 2.1. Chemicals, methods and instruments All chemicals used for the analyses were PA. Two-time distilled water was produced from a distillation device made in England. All standard solutions of cation Cu 2+ , Cd 2+ and Pb 2+ were purchased fromMerk (Germany). The content of Cu, Cd, Pb was determined by Atomic Absorption Spectroscopy (AAS) and was performed by a Shimadzu AAS - 6300 (Japan). 89 Tran Cong Viet, Dao Thu Ha and Nguyen Quang Tuyen 2.2. Results and discussion In the atomic absorption spectrometry, according to theory, atoms of each element absorb selectively one or some fixed wavelengths [1-3]. However, absorption peaks based on fact and that based on theory can be different. Therefore, absorption spectra of Cu, Pb and Cd with different concentrations in 1M HCl selected solution were determined. The results are presented in Table 1. Table 1 shows the differences between the theoretical and practical value, but they are not so large. Hence, the most sensitive wavelength of Cu (327.40 nm), Cd (228.80 nm) and Pb (217.00 nm) were chosen for the next experiments. However, the signal 217.89 nm corresponding to Cu absorption is close to the absorption one of Pb (217.00 nm). Therefore, effects of Cu on the Pb determination must be investigated. The expermental results showed that when Pb 2+ concentration was 2 ppm, the adsorpbane was 0.0829. When Cu 2+ concentrations of 1; 5; 10; 20; 30; 50; 80 and 100 ppm were added into that Pb 2+ concentration, average error was 1.43%. It means that the effects of Cu on the Pb was small and could be ignored. Table 1. F-AAS results of Cu, Pb and Cd determination at some wavelenghth in 0.1M HCl solution (CCu2+ = 2ppm,CCd2+ = 2ppm,CPb2+ = 4ppm) Element Wavelength Adsorpbance Theory In fact 1sttime 2ndtime 3rdtime Average 327.70 324.80 0.1513 0.1510 0.1511 0.1511 Cu 327.40 327.30 0.3034 0.3051 0.3051 0.3044 218.70 218.30 0.0621 0.0619 0.0639 0.0626 217.89 217.31 0.0754 0.0739 0.0745 0.0746 283.30 283.23 0.0458 0.0449 0.0454 0.0454 Pb 261.41 261.20 0.0639 0.0645 0.0635 0.0640 217.00 217.03 0.1042 0.1041 0.1043 0.1042 202.20 202.05 0.0367 0.0361 0.0372 0.0367 Cd 326.90 326.57 0.0536 0.0521 0.0527 0.0528 228.80 229.00 0.4653 0.4650 0.4648 0.4650 For Atomic Absorption Spectroscopy methods, analytical results depends on ionization procedure of the samples. Hence, parameters of the measurements should be determined and presented in Table 2. 90 Study on the optimal condition to determine Cu, Pb and Cd... Table 2. Optimal parameter for the determination of Cu, Pb and Cd, using Atomic Absorption Spectroscopy - Shimadzu AAS - 6300 No. Parameter for the measurements Element Cu Pb Cd 1 Ionization Rate of air (L/min.) 15 15 15 of sam Rate of acetylene (L/min.) 1.8 2.0 1.8 Rate of sample (µL/min.) 20 20 20 2 Radiation Intensity of cathodic lamp HCl (mA) 6 10 7 resonance Wave length (nm) 327.40 217.00 228.80 3 Height of the burner (mm) 7 7 7 4 Slit distance (mm) 0.7 0.7 0.7 5 Time of ionization (second) 15 15 15 6 Parameter of support lamp BGC-D2 BGC-D2 BGC-D2 Effects of background solution on the absorption of Cu, Pb, Cd were investi- gated. The optimal concentration of the acidic solutions are shown in Table 3. Table 3. Optimal concentration of the acidic solutions For element HCl Solution (M) HNO3 Solution (M) H2SO4 Solution (M) Cu 0.10 0.05 0.12 Pb 0.10 0.05 0.10 Cd 0.10 0.05 0.03 Figure 1. Absorpbance density of Cu in different acidic media Figure 2. Absorpbance density of Pb in different acidic media 91 Tran Cong Viet, Dao Thu Ha and Nguyen Quang Tuyen Figure 3. Adsorpbance density of Cd in different acidic media The dependences of adsorpbance on the concentration of metal ions in the dif- ferent acidic media were studied. Results are shown in Figure 1, 2 and 3. In the acidic media studied above, the solution of 0.05 M HNO3 was the best background for all three metals. Table 4. Results of valuation for the calibration cure to determine Cu, Pb and Cd by AAS Concentration (ppm) Cu Pb Cd n-put sample 0.5000 1.5000 2.5000 0.2000 10.000 10.000 0.5000 1.5000 2.5000 Out-put sample 0.4996 1.4989 2.5013 0.1984 0.9958 9.9838 0.5011 1.4911 2.5014 Error (%) -0.08 -0.07 0.05 -0.80 -0.42 -0.16 0.22 -0.59 0.06 From these results, the calibration cure built for determination of Cu, Pb and Cd in medium of 0.05 M HNO3 solution are: For Cu: A = 0.0781C+0.0053 with linear range of 0.05 - 2.50 (ppm) (1); For Pb: A = 0.0254C+0.0037 with linear range of 0.10 - 10.0 (ppm) (2); For Cd: A = 0.2204C+0.1472 with linear range of 0.05 - 2.50 (ppm) (3). In order to valuate the repeat of calibration-curve methods for each metal, some experiments were peformed in the linear range. The results are listed in Table4. Table 5. Results of Cu, Pb and Cd determination in domestic water of Cau Giay and Tu Liem Districts Sample pH Quantity - (mg/l) Cu Pb Cd A1 6.40 0.0110 0.0002 0.0011 A2 6.35 0.0191 0.0006 0.0001 A3 6.30 0.0047 0.0003 0.0007 A4 6.60 0.0310 0.0003 0.0028 A5 6.45 0.0265 0.0007 0.0008 A6 6.65 0.0148 0.0004 0.0007 92 Study on the optimal condition to determine Cu, Pb and Cd... A7 6.50 0.0095 0.0002 0.0001 A8 6.60 0.0143 0.0003 0.0006 A9 6.70 0.0150 0.0009 0.0005 A10 6.54 0.0238 0.0009 0.0010 A11 6.60 0.0277 0.0202 0.0109 A12 6.72 0.0104 0.0177 0.0037 A13 6.40 0.0189 0.0120 0.0062 A14 7.40 0.0244 0.0177 0.0063 A15 6.90 0.0069 0.0139 0.0040 A16 6.20 0.0163 0.0171 0.0012 VN Standards [6] (TCVN 5942-1995) 6.5  8.5 0.10 0.05 0.01 Using the calibration cure above, the contents of Cu, Pb and Cd in domestic water of Cau Giay and Tu Liem districts were determined (Table 5). In compari- son with the Vietnamese Standards for domestic water (TCVN 5942-1995) [6], the content of Cu in 10 samples were higher. Table 6. Results of Cu, Pb and Cd determination in water in Nghia Tan. Thu Le Lake and Nhue River (North of Dien Bridge) Sample pH Quantity - (mg/l) Cu Pb Cd B1 8.40 0.0097 0.0927 0.0007 B2 7.60 0.0162 0.0251 0.0006 B3 8.34 0.0136 0.0647 0.0005 B4 7.70 0.0149 0.0222 0.0069 B5 7.76 0.0293 0.1133 0.0014 B6 7.60 0.0184 0.1433 0.0004 B7 7.45 0.0295 0.1433 0.0004 B8 7.47 0.0215 0.1668 0.0008 B9 7.30 0.0056 0.0863 0.0015 B10 7.20 0.0019 0.1258 0.0003 B11 7.15 0.0059 0.1640 0.0005 B12 7.15 0.0024 0.1133 0.0008 VN Standards [6] (TCVN 5942-1995) 5.5  9.0 1.00 0.10 0.02 93 Tran Cong Viet, Dao Thu Ha and Nguyen Quang Tuyen The contents Cu, Pb and Cd determination in the lake of Cau Giay and Tu Liem districts samples were also studied (Table 6). Where, B1 and B2 were the samples collected in Nghia Tan Lake on 25/4/2006 and 16/06/2006, respectively. B3, B4 were the samples received in Thu Le on 25/4/2006 and 16/06/2006, respectively. B5-B12 were the samples collected in the same place, but on 06/06/2006. In comparison with the Vietnamese Standards of water for other purposes (TCVN 5942-1995), the content of Cu in 7 samples were higher. 3. Conclusion Atomic Absorption Spectroscopy was sensitive (0.01 - 0.02 mg/ml) and sensi- tivity depended on the absorption wavelength of each element. The optimal conditions for determination of Cu, Pb and Cd by Atomic Ab- sorption Spectroscopy were investigated. A number of 16 samples of domestic water in Cau Giay and Tu Liem districts were measured, showing that the content of Cu in 10 samples were higher than Vietnamese Standards (TCVN 5942-1995). Among 12 samples of Lakes or Rivers in that area, 7 one contained Cd higher than that of Vietnamese Standards (TCVN 5942-1995). REFERENCES [1] Pham Luan, 2006. Methods of Atomic Absorption Spectroscopy Analyses. Hanoi National University Publishing House, (in Vietnamese). [2] Hoang Minh Chau, Tu Van Mac, Tu Vong Nghi, 2002. Fundamentals of Analytical Chemistry. Science and Tehnique Publishing House, Ha Noi, (in Viet- namese). [3] Ho Viet Quy, 2005. Analytical instumental Methods in Modern Chemistry. Hanoi National University of Education Publishing House, (in Vietnamese). [4] Le Lan Anh, Pham Gia Mon, Vu Duc Loi, Do Viet Anh, 1997. Determina- tion of the heavy metals in sea water using AAS and Volt-Ampe Dissolution methods. Journal of Chemistry, Vol. 2, N ◦ . 3, pp. 31-34 (in Vietnamese). [5] Vietnamese Standards of Environment, 1995. Water Quality. (in Viet- namese). 94