Cloud-Point Extraction And Its Application To The Separation/Preconcentration And Speciation Of Metal Ions

Sensitive, rapid, reproducible, simple and accurate analytical methods are required for the determination of trace elements in geological, biological and environmental samples. The direct determination of extremely low concentrations of trace elements by modern atomic spectroscopic methods, such as atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) is often difficult. The limitations are associated not only with the insufficient sensitivity of these techniques but also with matrix interference. For this reason, the separation and preconcentration of trace elements is often required.Cloud point extraction (CPE) is a kind of new environmentally benign liquid-liquid extraction method. The technique is based on the property of most non-ionic surfactants in aqueous solutions to form micelles and become turbid when heated to a temperature known as the cloud point temperature. Above the cloud point, the micellar solution separates into a surfactant-rich phase of a small volume and a diluted aqueous phase, in which the surfactant concentration is close to the critical micellar concentration (CMC). Any analyte solubilized in the hydrophobic core of the micelles will separate and become concentrated in the small volume of the surfactant-rich phase. The small volume of the surfactant-rich phase obtained with this methodology permits the design of extraction schemes that are simple, economical, highly efficient, speedy, and of lower toxicity to the environment than those extractions that use organic solvents. Separation and preconcentration based on cloud point extraction is becoming an important and practical application in the use of surfactants in analytical chemistry. It's widely used in the separation and purification of bio-molecules and extraction of organic compounds and metal ions.This sort of extraction can be implemented in conjunction with differentanalytical detection systems. Cloud point extraction in connection with spectrophotometry can emerge as a powerful analytical technique for metal preconcentration and determination. CPE has also been the subject of study in metal analysis in connection with atomic spectrometry. The addition of a diluting solution in the surfactant-rich phase is always indispensable in order to obtain a clear and homogenous solution of low viscosity compatible with the requirements of flame and plasma nebulizers. However, the presence of methanol and surfactant in the flame of AAS and plasma have effects on various parameters, such as excitation conditions, plasma stability, nebulizer flows and so on. It was recently proposed to use it in conjunction with detection by electrothermal vaporization, ultrasonic nebulization or hydride generation ICP-AES for the determination of metal ions. According to our knowledge, up to now, applications based on CPE-ICP-AES, along with conventional pneumatic nebulization of the developed methods in trace analysis have seldom been reported.The aim of this dissertation is to systematically study on the cloud-point extraction and its application to the separation/preconcentration and speciation of metal ions. The major contents are described as follows:1. A new method for the determination of trace chromium and copper in water samples by inductively coupled plasma optical emission spectrometry after cloud point extraction was proposed. The effect of experimental conditions such as pH, concentration of chelating agent and surfactant, equilibration temperature and time on cloud point extraction was studied. The. chemical variables affecting the separation and extraction recovery were optimized. The proposed method was applied to the simultaneous determination of these elements in real samples.2. A new method for the determination of trace cobalt in water samples by flame atomic absorption spectrometry after cloud point extraction was proposed. The effect of experimental conditions such as pH, concentration of chelating agent and surfactant, equilibration temperature and time on cloud point...