| ObjectiveLead is a kind of toxic heavy metals which can be accumulated into the human body though water, food and atmosphere. Trace lead can damage the body of nervous, cardiovascular, procreant systems and so on. So it is very important to develope a novel method with highly sensitive and accurate for the determination of lead.Lead in water is one of the main contents to be detected. Hydride generation atomic fluorescence spectrometry (HG-AFS) has some advantages for determination of lead in water with higher sensitivity, lower detection limit and easier operation, etc. But lead in water sample has to be separated and enriched because of lower concentration. Cloud point extraction (CPE) is a kind of new environmentally benign extraction method without using volatile organic solvents, which was based on the solubility and cloud point phenomenon of non-ionic surfactant. By alterating the experimental conditions, the solution is separated into two phases. The analyte is separated from the aqueous solution as hydrophobic complex compounds, and enriched in surfactant rich phase. It is a safe, high efficiency and economical methodology for preconcentration and separation.In the first chapter, a new method for determination of lead by hydride generation atomic fluorescence spectrometry after cloud point extraction is proposed. A few drops of antifoam have to be added in order to restrain foam before the process of instrumental determination. That is a green analytical technology for the determination of lead in water samples.Lead is one of the poisonous metal elements in tobacco. When smoking, a part of lead in cigarette will be absorbed into human body by smokers, another part of lead will volatilize into the air to pollute environment and be harmful for passive smokers. In the second chapter, the method of determination by HG-AFS for lead in cigarette after digestion treatment is proposed. It is applied to determine lead in cigarette of different regions.As the biggest contact site, skin is one of the important approaches which lead enter into the human body. Bath powder and talcum powder of infant is interested by parents as a skin care product for their baby. Lead poisoning in infancy by using the powders had been reported. However, to the best of my knowledge, there are no reports discussing the determination of lead in them. A new method for determination of lead in bath powder and talcum powder of infant is developed in the third chapter.Methods1. Determination of Lead in Water Samples by HG-AFS after CPE.The formation of a complex with dithizone in borate buffer solution, trace lead was extracted and separated from aqueous phase by cloud point extraction (CPE) using Triton X-114 as the surfactant. After water bath settlement, ice bath, phase separation, lead in the surfactant phase, which was diluted with distilled water and dilute acid was determined by HG-AFS under antifoam. The conditions of CPE and the determination for lead were optimized. The proposed method was applied to determination of lead in water samples.2. Determination of lead in cigarette, bath powder and talcum powder by HG-AFSAfter sample pretreatment, trace lead in cigarette, bath powder and talcum powder were determined by HG-AFS under the optimum conditions.Results1. As the experimental results shown, the optimized conditions were pH 8.0,1.2×10-5 mol·L-1 of dithizone concentration, Triton X-114 (0.2%, w/v), Dow Corning(?)1430 Antifoam 4 drops, 15.0 g-L-1 of potassium borohydride solution,20.0 g-L-1 of potassium hexacyanoferrate,1% of hydrochloric acid(HCl) carrier flow concentration,2% of HC1 concentration of solution,280 V of negative high-voltage,50/30 mA of the lamp current,700 mL-min-1 of the carrier gas flow rate.2. Under the optimum conditions, the preconcentration of 50 mL of the solution by CPE gave an enrichment factor of 10 times. Linearity was obeyed in the range of 0.05～3.2μg-L-1 with correlation coefficient of 0.9996. The detection limits of the CPE-AFS was 0.016μg-L-1 for lead. The method has been applied to the determination of lead in water samples, with the recovery of standard addition of 89.1%～111.0%, and the precision of 1.09%～4.46%(RSD). The content of lead in water samples were drinking water 0.825±0.037μg·L-1, lake water 0.838±0.024μg·L-1, river water 1.861±0.054μg·L-1.3. Under optimal conditions, the method had a good linearity in the range of 2.5-3.0μg·L-1 of lead in cigarette, correlation coefficient r=0.9990. The detection limit of the method was 0.114μg·L-1. The coefficient of variation was between 1.88% and 5.28%, the recoveries was in the range of 87.5%～101.5%. The content of lead in cigarette which came from different places was between 2.32μg-g-1 and 5.67μg-g-1.4. The determination of lead by HG-AFS in bath powder and talcum powder with the recovery of standard addition of 92.2%～109.1% was obtained, and the precision was less than 3.1 %(RSD). The content of lead for them was from 0.07 to 4.24μg-g-1. ConclusionHG-AFS, after dropping antifoam, was combined with CPE successfully. That is a new method of determination for lead in water samples which was extracted by CPE with dithizone as the complexing agent and Triton X-114 as the surfactant. The results show that this method has lower detection limit, higher sensitivity, better accuracy, lower toxicity and higher safety.The trace level of lead in cigarette, bath powder and talcum powder was determined with satisfactory results by HG-AFS. The study shows that there are different level of lead in bath powder and talcum powder. Therefore, the parents should use bath powder and talcum powder for infant with caution. |
PDF Full Text Request