| A new cloud point extraction(CPE) technique was established and used for the determination of trace lead(Pb), cadmium(Cd), arsenic(As) and mercury(Hg) in environmental water samples combined with graphite furnace atomic absorption spectrometry(GFAAS) and hydride generation atomic fluorescence spectrometry(HGAFS) respectively.1. The present situation and harm of heavy metal pollution and the significance and common method of speciation analysis of heavy metal were expatiated. Otherwise, in this paper, the principle, influence and application of CPE, especially in heavy metal determination and speciation analysis were reviewed.2. A method combining CPE with GFAAS was proposed for the determination of trace amounts of Pb and Cd in environmental water. Pb(Ⅱ) and Cd(Ⅱ) was quantitatively extracted in the form of coordination complex with 8-oxine by CPE with Triton X-45 as a surfactant-rich phase. The effect of experimental conditions such as p H, concentration of reagents, heating temperature and time on CPE were investigated, and these conditions were optimized efficiently by Plackett–Burman and Box–Behnken experimental designs. Under the optimum conditions, good linearity was observed in the concentration ranges of 0.5–4.0μg/L for Pb and 0.05–0.50μg/L for Cd with the relative standard deviation of 0.6% and 0.54%. The limits of detection were 0.043μg/L for Pb with a concentration factor of 24.2 in a 10 m L sample and 0.0016μg/L for Cd with a concentration factor of 18.4 in 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 96.2% ~103.6%.3. A new cloud point extraction technique was established and used for the determination of trace As species in water samples combined with hydride generation atomic fluorescence spectrometry(HGAFS). As(III) and As(V) were complexed with ammonium pyrrolidinedithiocarbamate(APDC) and molybdate, respectively. The complexes were quantitatively extracted with the non-ionic surfactant(Triton X-114) by centrifugation. After addition of antifoam, the surfactant rich phase containing As(III) was diluted with 5% HCl for HGAFS determination. For As(V) determination, 50% HCl was added to the surfactant-rich phase, and the mixture was placed in an ultrasonic bath at 70 °C for 30 min. As(V) was reduced to As(III) with thiourea–ascorbic acid solution, followed by HGAFS. Under the optimum conditions, limits of detection of 0.009 and 0.012μg/L were obtained for As(III) and As(V), respectively. Concentration factors of 9.3 and 7.8, respectively, were obtained for a 50 m L sample. The precisions were 3.4% for As(III) and 3.7% for As(V). The proposed method was successfully used for the determination of trace As(III) and As(V) in water samples with satisfactory recoveries.4. A new method for determination of inorganic mercury(Hg) and methyl mercury(Me Hg) in water samples by hydride generation atomic fluorescence spectrometry after cloud point extraction was proposed. The method was based on that Hg(Ⅱ) was complexed with I- and methyl green(MG) could form a hydrophobic ion-associated complex which was then extracted into the surfactant-rich phase of Triton X-114 at p H 6.0, then the hydrophobic ion-associated complex was subsequently separated from Me Hg by centrifugation. The surfactant rich phase containing Hg(II) was added antifoam and diluted with 5% HCl for HGAFS determination. The supernatant is also subjected to the similar CPE procedure by adding APDC which can form complex with Me Hg. After CPE, 0.100mol/L KBr O3-10g/L KBr was added and left in a thermostated bath at 40°C for 20 min in order to digest Me Hg to Hg(II), and the above solution can be analyzed after disposal as describe above. The limits of detection obtained in the optimal conditions was 0.007mg/L for Hg(Ⅱ) and 0.018mg/L for Me Hg, and good linearity was observed in the concentration ranges of 0.2~4.0mg/L for Hg(II) and Me Hg with the relative standard deviations of 2.7% for Hg(II) and 2.9% for Me Hg(n=6), respectively. Concentration factors of 15.1 for Hg(II) and 11.2 for Me Hg were obtained for a 50 m L sample. The developed method was applied to the speciation of Hg and Me Hg in environmental water and the recoveries were found to be in the range of 95% ~103.75%. |
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