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Application of Cloud Point Extraction to the Speciation Analysis of Metal Ions

Author: YangLiNing
Tutor: ChenJianRong
School: Zhejiang Normal University
Course: Analytical Chemistry
Keywords: cloud point extraction trace metal elements speciation analysis surfactant trace spectrophotometry high performance liquid chromatography fluorescentspectrometry
CLC: O658.2
Type: Master's thesis
Year: 2013
Downloads: 57
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Abstract


Cloud point extraction(CPE) is called environment friendly extraction technology, due to the failure of volatile organic solvents, safely, simply, higher extraction and widely used. This technology is often used to separate and enrich samples which in the geology, biology and environment. CPE is used to improve the sensitivity and selectivity of the detection method and reduce the detection limit, which has received more and more attention in the separation and enrichment trace metal especially.CPE has the ability to extract concentration based on the cloud point phenomenon and dissolving capacity of the surfactant. The solution will appear cloudy when nonionic surfactant aqueous solution was heated to a certain temperature, which is called cloud point phenomenon. System is divided into two different phase: one is called enrichment of micellar phase, which contains the most of the surfactants in the system; the other is water phase, in which the content of surfactant is close to its critical micelle concentration. This micellar system has been proved to be condensed and extraction ability of hydrophobic substances from the water phase, which means surfactant has a strong capacity of solubilization. The objects (that is, the object under test) of solubilised with micellar into small volume of rich micellar phase, thus realize the purpose of the separation of the metal chelates and complex matrix.Speciation analysis of metal elements is particularly important in biological and environmental samples because of the toxicity, the beneficial and the biological of an element depends on the chemical form exist in the sample mostly. To achieve the same metal ions of different forms can be used in two methods:one is choose broad used metal chelating agent to extraction of different forms of ions at the same time, then measured by chromatographic or electrophoretic separation; the other is measured separately according to the different chemical properties of elements in different forms.Based on the reported researches, cloud point extraction combination chromatography and spectroscopy were carried out to enrich metal ions in environment samples. The experiment is divided into three parts:1. A new sensitive and simple method for determination of iron(Ⅱ) and iron(Ⅲ) in water samples by cloud point extraction with trace spectrophotometry was established using1-(2-pyridine-azo)-2-naphthol (PAN) as complexing agent and Triton X-114as surfactant in this paper. It was based on the cloud point phenomenon of surfactant, iron(Ⅱ) could form stable complex with PAN, which was then quantitative extraction into surfactant phase. The enrichment phase was directly determined by trace spectrophotometry. Iron(Ⅲ) was determined by different measurements after reduction of iron(Ⅲ) to iron(Ⅱ) with hydrochloric hydroxylamine. The effect of maximum absorption wavelength and the parameters influencing cloud point extraction efficiency were investigated. Under the optimal conditions, Beer’s law was obeyed in the range of2~200μg L-1for iron (Ⅱ) or total iron. The limits of detection were0.71μg L-1in the wavelength of760nm. The proposed method has been directly applied to determine iron(Ⅱ) and iron(Ⅲ) in water samples and recovery tests between92.8%-100.1%.2. Ammonium pyrrolidinedithiocarbamate(APDC) was selected as the chelating agent and non-ionic surfactant Triton X-114as the extractant. Baseline separation of the APDC chelates of Cr(Ⅲ) and Cr(Ⅵ) was realized on a RP-C18column by using a mixture of methanol-water (65:35, v/v) solution and4.5mmol L-1CTMAB buffered with0.02mol L-1NaAc-HAc solution (pH5.5) as the mobile phase at aflow rate of0.8mL min-1. The variables affecting the complexation and extraction steps were examined. The precision (R.S.D.) for five replicate injections of a mixture of100μg L-1Cr(Ⅲ) and Cr(Ⅵ) was0.22%and0.31%for the retention time,2.4%and4.0%for the peak area, respectively. The concentration factor was20for Cr(Ⅱ) and22for Cr(Ⅵ). The detection limit (LOD) of this method, calculated as three times the standard deviation of the blank signals was1.1μg L-1for Cr(Ⅲ) and1.3μg L-1for Cr(Ⅵ), respectively. The proposed procedure was applied to the speciation of chromium in sediment samples with satisfactory results. A sensitive and simple method for high-performance liquid chromatography (HPLC) determination of traces of chromium species in environmental water samples after preconcentration by cloud point extraction (CPE) has been developed.3. In this work, cloud point extraction (CPE) with non-ionic surfactant Triton X-114and the fluorometric ligand,2,3-diaminonaphtalene(DAN)were used for extraction of trace amounts of inorganic selenium species by spectrofluorometry. CPE parameters affecting complexation and phase separation for Se(Ⅳ) were optimized, Se(Ⅵ) can be determined by total selenium minus Se(IV). Under the optimal conditions, the limit of detection calculated as three times the standard deviation of the blank signals was0.11μL-1for Se(Ⅳ). The precision (R.S.D.) for five replicate injections of10μg L-1Se(IV) was1.7%and0.84%for the retention time,1.6%and2.0%for the peak area, respectively. Accuracy of the method was checked using environment water and Se-enriched products. The suggested method can be used for selenium species of selenite, selenate, and total organic selenium at μg L-1level.

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CLC: > Mathematical sciences and chemical > Chemistry > Analytical Chemistry > Separation of elements and compounds > Extraction method
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