UV Spectroscopy Determination of Aqueous Lead and Copper Ions in Water

Transcription

1 UV Spectroscopy Determination of Aqueous Lead and Copper Ions in Water C. H. Tan a, Y. C. Moo a, M. Z. Matjafri a and H. S. Lim a a School of Physics, Universiti Sains Malaysia, 118 Pulau Pinang, Malaysia. ABSTRACT Lead (Pb 2+ ) and copper (Cu 2+ ) ions are very common pollutants in water which have dangerous potential causing serious disease and health problems to human. The aim of this paper is to determine lead and copper ions in aqueous solution using direct UV detection without chemical reagent waste. This technique allow the determination of lead and copper ions from range.2 mg/l to 1 mg/l using UV wavelength from 25 nm to 225 nm. The method was successfully applied to synthetic sample with high performance. Keywords: UV spectroscopy, heavy metal, copper, lead. 1. INTRODUCTION Lead (Pb 2+ ) and copper (Cu 2+ ) ions are very common pollutants in water which have dangerous potential causing serious disease and health problems to human. Lead is toxic and prolongs exposure to lead ions will caused serious brain and nervous system damage. Low quantity of copper ions are required for body metabolism, however excessive copper ions intake will caused anemia, tissue injury and liver damage. According to WHO, its concentration was limited to.1 mg/l for lead and 2 mg/l for copper in drinking water regulation. [1]-[3] Most of the current analytical method for Pb 2+ and Cu 2+ are inductively coupled plasma - optical emission spectroscopy (ICP-OES), inductively coupled plasma - mass spectrometry (ICP-MS), atomic absorption spectrometer (AAS), and graphite furnace atomic absorption spectrometer (GFAAS). [4]-[5] However, those methods required highly trained operator and expensive equipment. Besides that, those methods are much more complicated in terms of calibration and sample preparation. Spectroscopy method without chemical reagent proves useful and it is a non-destructive method. In year 212, Ahmad Fairuz introduce a near infrared spectroscopy analysis on aqueous sucrose, glucose, and fructose solution without using any additional chemical reagent. [6] According to Beer-Lambert Laws, when light pass through a medium, it will experience scattering, reflection or absorption. The output light intensity will decreases depending on the concentration of the sample and path length of the light passes through. The decreases of light intensity can be calculated via equation A = log(i /I), where A is the absorption, I is the input light intensity, and I is the output light intensity. Besides that, every medium, molecules, or atoms has its own unique absorption capability on different wavelength. The relationship between path length, concentration and absorption can also written in the form of A = Ɛbc, where b is the path length and c is the concentration of the sample. Thus, UV absorption characteristic of Pb 2+ and Cu 2+ was studied in this paper. The objective of this paper is to determine Pb 2+ and Cu 2+ ions in aqueous solution using direct UV detection without using any additional chemical reagent. The UV light source used in this project is deuterium lamp with JAZ Spectrometer. 2. METHOD AND MATERIAL In this paper, the regression equations for Cu 2+ and Pb 2+ ions concentration were generated from the absorbance of copper (II) chloride (CuCl 2 ) and lead (II) chloride (PbCl 2 ) aqueous solution. The generated equation were then verified with prepared copper (II) sulfate (CuSO 4 ) and lead (II) acetate (Pb(COOCH 3 ) 2 ) aqueous solution. This comparison is to make sure the both the concentration of Cu 2+ and Pb 2+ from other salt can fit the equation generated from CuCl 2 and PbCl 2 solution.

2 2.1 Sample preparation In this study, samples are prepared by using copper chloride powder, copper sulfate powder, lead chloride powder and lead acetate powder with distilled powder. Sample solutions are prepared using micropipette and were then measured using UV spectroscopy immediately sample preparation process. Measurement and verification are done using 5 samples for each type of solution from concentration.2 mg/l to 1 mg/l. Besides that, five high concentrated samples ranged from 1 mg/l to 5 mg/l for both PbCl 2 and CuCl 2 will be prepared for preliminary result. 2.2 UV spectroscopy setup Spectrometer used in this study is JAZ Spectrometer and the spectrum data was acquired using Ocean Optic SpectraSuite. Besides that, fiber optic that used in this study is QP6-25-SR and UV light source is the deuterium lamp. It has two channels with channel for wavelength 2 nm to 85 nm and channel 1 for wavelength 65 nm to 11 nm. A quartz cuvette with path length 1 cm was used as the sample container. Besides that, cuvette holder with four 74-UV collimator with f/2 fused silica lens which can be connected to the fiber optic. The overall experimental setup is shown in Figure 1. Fiber optic Jaz Spectrometer Cuvette holder UV Light source Collimator Cuvette / Sample Figure 1. Experiment setup 3 ml of sample will be used form each solution for the test with distilled water as the reference sample. For every sample measured, the cuvette will be washed with distilled water to prevent any left over from previous sample. Both the spectrometer and deuterium lamp are warm up for at least 3 minutes before starting the measurement. 2.3 Data analysis Figure 2 and Figure 3 show the spectrum data for PbCl 2 and CuCl 2 solution at five different concentrations which are 1 mg/l, 2 mg/l, 3 mg/l, 4 mg/l and 5 mg/l. Naturally Cu 2+ aqueous solution is blue in color. However, the visible region spectrum is not visible at low concentration for CuCl 2. Therefore the visible region for CuCl 2 in this study is ignored. Moreover, the colorless PbCl 2 does not have any significant visible spectrum too. Besides that 5 samples of PbCl 2 and CuCl 2 aqueous solution ranged from.2 mg/l to 1 mg/l are used to obtain the regression equation. Furthermore, the regression equation was chosen based on highest R-square (R 2 ) value among the other. Multiple linear regression are trial and error method that can involve more than one wavelength in one equation and hence increase the accuracy and R 2 value.

3 Absorbance mg/l 2 mg/l 3 mg/l 4 mg/l 5 mg/l Wavelength, nm Figure 2. Lead (II) chloride UV spectrum From the PbCl 2 spectrum, we observed that there is a peak from 25 nm to 225 nm. The linear regression was done using the data within the peak from fifty samples ranged from.2 mg/l to 1 mg/l and generated using software Minitab 14. Equation (1) and Equation (2) are the regression equation for PbCl 2 solution with selected wavelength 25 nm, 21 nm, 215 nm, 221 nm, and 225 nm. PbCl 2 C Pb = D 211 (1) C Pb = D D D (2) where C Pb is the concentration for Pb 2+ ions in water D N is the absorbance value on wavelength N nm. Equation (1) is a simple linear regression where only used one wavelength. Equation (2) is the multiple regression equation which have more than one wavelength in the equation with slightly higher R-square (R 2 ) value. R 2 value for Equation (1) is.993 and.994 for Equation (2) Absorbance mg/l 4 mg/l 3 mg/l 2 mg/l 1 mg/l Wavelength, nm Figure 3. Copper (II) Chloride UV Spectrum

4 However, CuCl 2 solution did not show any significant peak as PbCl 2 do but it does shows a broad peak which start from 2 nm to 23 nm. The regression was then done at the chosen wavelength from fifty samples ranged from.2 mg/l to 1 mg/l. Equation (3) and Equation (4) are the regression equation for CuCl 2 solution with wavelength 25 nm, 21 nm, 215 nm, 221 nm, and 225 nm. C Cu = D 221 (3) C Cu = D D D (4) where C Cu is the concentration for Cu 2+ ions in water D N is the absorbance value on wavelength N nm. R 2 values for both Equation (3) and Equation (4) are.958 and.979 respectively. Since the detection range for JAZ Spectrometer is from 2 nm to 85 nm, the data near 2 nm are unusable. Data that near to the detection limits will most likely exhibit more noise that others and it was not recommended. Therefore, for both spectrum, the extreme negative value near 2 nm and it was neglected in this study. Figure 2 and Figure 3 also show that as the concentration of sample increases, the overall absorbance increase from wavelength 25 nm to 23 nm. However, noise also increases as the absorbance increases as shown in Figure 2 and Figure 3. Figure 4 will shows the absorbance graph for PbCl 2 at wavelength 211 nm and CuCl 2 at wavelength 221 nm..4 Absorbance vs Concentration.35 R² = Absorbance R² =.9557 CuCl2 (221 nm) PbCl2 (211 nm) Linear (CuCl2 (221 nm)) Linear (PbCl2 (211 nm)) Concentration, mg/l Figure 4. Absorbance vs concentration 2.4 Verification The equation was then verified with another set of prepared sample (CuSO 4 and Pb(COOCH 3 ) 2 ). Figure 5 and Figure 6 show the verification data for all four equation mentioned before.

5 12 Verification Data for Pb 2+ aqueous ions solution 1 Predicted Value, mg/l Equation (1) Equation (2) Real Value, mg/l Figure 5. Verification Data for Pb 2+ aqueous ions solution Predicted Value, mg/l Equation (3) Equation (4) Real Value, mg/l Figure 6. Verification Data for Cu 2+ aqueous ions solution ( x x ) The error for each equation was then calculated using equation, where x is the real value for the sample i= 1 N and x is the predicted value using spectroscopy data from the sample. As shown in Figure 4, the regression equations i that generated from PbCl 2 are able to apply on Pb(COOCH 3 ) 2 with error value.9 mg/l for Equation (1) and.37 mg/l for Equation (2). Besides that, regression equations from CuCl 2 are also able to apply on CuSO 4 without problems. Equation (3) has the error value of.219 mg/l and error value for Equation (4) is.212 mg/l. For both cases, the multiple regression equation has slightly less error as and more accurate as compare to simple regression. N i 2

6 3. CONCLUSION In conclusion, equation created form PbCl 2 and CuCl 2 solution are able to determine the concentration of Pb 2+ and Cu 2+ correctly. The Pb 2+ ions will have slightly higher UV absorbance compare to Cu 2+ ions. This method still have some limitation that not able to use for very low concentration or very high concentration. However, this technique have some advantages over the chemical method, it is a much simpler and non-destructive technique without the need of preparing chemical reagent. In future works, this technique might be simplified into a more portable device with lower cost using UV LED, fiber optic, photodiode and PIC controller. ACKNOWLEDGMENT The authors gratefully acknowledge the financial support from the short term Research University Postgraduate Research Grant Scheme (USM-RU-PGRS), account number: 11/PFIZIK/83356 and USM graduate assistant used to carry out this project. Thanks are also extended to USM for support and encouragement. REFERENCES [1] WHO, Copper in Drinking-Water 24, < (19 December 213). [2] WHO, Lead in Drinking-Water 211, < (19 December 213). [3] WHO, Guidelines for Drinking-Water Quality 26, < (19 December 213). [4] WHO, Brief guide to analytical methods for measuring lead in blood 211, < (19 December 213). [5] Ashley, T. T., Kelly, A. M., Stuart, M. and Stephen, A., "The determination of copper, zinc, cadmium and lead in urine by high resolution ICP-MS," Journal of Analytical Atomic Spectrometry, 13, (1998). [6] Omar, A. F., Atan, H., and MatJafri, M. Z., "Peak Response Identification through Near-Infrared Spectroscopy Analysis on Aqueous Sucrose, Glucose, and Fructose Solution," Spectroscopy Letters, 45, (212).