| Objective Direct determination of heavy metal ions at trace levels is limited due to their low concentrations and matrix interferences. Thus, preconcentration and separation techniques are still very necessary. Cloud point extraction(CPE) is a high efficiency and safe methodology for separation of the water samples. This paper proposes a method to determinate the trace copper(Cu), zinc(Zn), iron(Fe), lead(Pb) and cadmium(Cd) in water samples by atomic absorption spectrometry(AAS) by CPE, in order to determine and evaluate the quality of the concentration of heavy metals in canal water system, which is the principal surface water in Haizhu District.Method 1. CPE-graphite furnace atomic absorption spectrometryAlizarin yellow R was selected as chelating agent. Pb was quantitatively extracted in the form of coordination complex by CPE with Triton X-114 as a surfactant-rich phase. Using the mixture of non-ionic surfactant Triton X-114 and cetylpyrinium bromide(CPB) for the preconcentration of trace amount of cadmium(Cd) in water samples to determination by GFAAS. The effect factors on CPE, such as p H value, chelating agent, equilibration temperature, Triton X-114 agent, equilibration time.2. CPE-flame atomic absorption spectrometryThe procedure is based on formation of an ion-pair between the 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(5-Br-PADAP) and tetraphenylborate(TPB) followed by formation with target element, extraction with Triton X-114, and determined by FAAS. Influential variables on the ion-pair cloud point extraction efficiency, such as the p H, volume of Triton X-114, equilibration temperature, incubation time ion-pair agent and concentration have been fully evaluated and optimized.3. The collection and analysis of water samplesOn the basis of the above methods, the studies consisted of on-site sampling, water samples analyses in the laboratory and evaluate the quality of the concentration of heavy metals in canal water system, which is the principal surface water in Haizhu District. The method was employed for the repeatability experiments and determination of Cu, Pb and Cd in the standard samples of natural water.Results1. CPE-graphite furnace atomic absorption spectrometryThe limits of detection obtained in the optimal conditions was 0.130μg/L for Pb and 0.008μg/L for Cd. Good linearity was observed in the concentration ranges of 0.4–4.0μg/L for Pb and 0.02–0.24μg/L for Cd with the relative standard deviation of 1.08% for Pb and 0.84% for Cd. Concentration factors of 15.26 and 14.29, respectively, were obtained for a 10 m L sample. The proposed method has been applied to the determination of Pb and Cd in water samples with the recoveries of 94.9–103.8%.2. CPE-flame atomic absorption spectrometryGood linearity was observed in the concentration ranges of 10–160μg L-1 for Cu, 2–30μg/L for Zn and 20–300μg/L for Fe. In a 50 m L sample of Cu, Zn and Fe, concentration factors of 38.37, 38.98 and 29.88 and limits of detection of 0.44μg/L, 0.14μg/L and 0.78μg/L were determined, respectively. The RSD(%)(n=6) were 0.53–1.67. Recoveries of Cu, Zn and Fe spiked into water samples were in the range of 95–105%.3. The collection and analysis of water samplesThe contents of Pb, Cd, Cu, Zn and Fe in thirty-eight water samples from river were 0.0015~0.0078mg/L, 0.0001~0.0003mg/L, 0~0.0089mg/L, 0.0360~0.1150mg/L, 0.03~0.28mg/L, respectively. Clustering analysis was made, and 38 samples were grouped into 4 pollution types. The principal component analysis showed that, the main controlling factor of pollutants in water in Haizhu District is Cd. According to Principal component scores, the quality of haizhu lake water is the best and the part of Pazhou Center is the worst. Evaluated heavy metals pollution of surface water based on heavy metals content and found that Fe has far exceeded the standard in water. Nemerow index method shows the minimum value is 0.6689, the maximum is 1.8067.Conclusions(1) Cloud point extraction is a simple, environment-friendly, efficient separation and preconcentration method of trace metals. Cloud point extraction to trace levels of Pb, Cd and Cu, Zn, Fe as a prior step to its determination by graphite furnace atomic absorption spectrometry and flame atomic absorption spectrometry has been developed. The methods were used for the determination of trace metals in water samples with satisfactory results.(2) Zn concentration exceeds the standards for a part of surface water source of Quality Standards I for Surface Water but in Quality Standards II. Fe average concentration exceeds the standards for the surface water source of drinking water which is the supplementary item in Environmental Quality Standards for Surface Water.(3) Clustering analysis was made, and 38 samples were grouped into 4 pollution types. According to Principal component scores, the quality of haizhu lake water is the best and the part of Pazhou Center is the worst. Evaluated heavy metals pollution of surface water based on heavy metals content and found that Fe has far exceeded the standard in water. |
PDF Full Text Request