| Cloud point extraction (CPE) is a new environmental liquid-liquid extraction method. The technique is based on the phase separation exhibited by aqueous solutions of non-ionic surfactants, which become turbid and separation in two phases when the temperature is increased above a particular value refered to as cloud point temprature (CPT). The two separated phases include a surfactant rich phase composed almost totally of the surfactant and aqueous phase in which the surfactant concentration is close to the critical mecellar concentration. Any species with hydrophobic properties are isolated from the bulk aqueous solution and thus extracted in the small volume of the surfactant rich phase. Compared with conventional liquid-liquid extraction, cloud point extraction (CPE) has several important advantages:low cost, safety, convenience, simplicity, higher extraction and preconcentration factors. In recent years, cloud point extraction combined with different instrumental methods of analysis, have successfully used in the separation and speciation analysis of trace metal ions.Laser thermal lens spectrometry (LTLS) is a photothermal analytical technique appeared in the late 1970s and the early 1980s. Laser thermal lens spectrometry, as a high sensitive analysis method for trace substances, is suitable for detection in small volume and non-aqueous media.The combination of cloud point extraction (CPE) and laser thermal lens spectrometry(LTLS), which intergrates the excellent advantages of both methods, displays the characters of low consumption of samples and small interference of matrix as well as high sensitivity.This thesis consists of two sections:the review and the research reports.The review section describes the principle and application of cloud point extraction (CPE), and summarizes the achievements of coupling between cloud point extraction (CPE) and instrumental detection systems for metal analysis, and proposed the ideas of this paper.In the research reports section, the joint method of cloud point extraction (CPE) and laser thermal lens spectrometry (LTLS) for trace metals was discussed. The analytical parameters, such as pH, surfactant concentration, incubation temperature, and sample volume, etc, were investigated. The developed method was applied to preconcentration and determination of metal ion in natural samples. The major contents are described as follows:Part one:A novel method for the determination of cobalt by cloud point extraction (CPE) coupled with themal lens spectrometry has been developed. It is based on CPE of cobalt (III) ions as 2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminoaniline (3,5-diCl-PADMA) complexes using octyl- phenoxypolyethoxyethanol (Triton X-114) as surfactant. Multiple experimental conditions that affected CPE efficiency, including pH, the concentrations of chelating agent and surfactant, equilibration temperature and time were identified. CPE condition were optimized as follow:pH=5.0 HAc-NaAc buffer solution,4.0×10-6 mol/L 3,5-diCl-PADMA,0.08% Triton X-114 (w/v), and 20 min equilibrated at 60℃. After phase separation, the surfactant-rich phase was dissovled by alcohol, and then was acidified by hydrochloric acid. The obtained solution was intruduced to a 5 mm quartz cell and the analyte was determined by thermal lens specrometry. A single model He-Ne laser was used both as exciting and probing beam. Under the optimum conditions,the calibration curve was linear in the range 0.2～4.0 ng/mL and the detection limit was 0.02 ng/mL. The method has been successfully applied to the extraction and determination of cobalt in water samples.Part two:a new combination method, employing laser thermal lens spectrometry (LTLS) after cloud point extraction (CPE), has been developed for the preconcentration and determination of rhodium. Rhodium was complexed with 2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminoaniline as a complexing agent in an aqueous medium and concentrated by octylphenoxypolyethoxyethanol as a surfactant. The chemical factors that affect the cloud point extraction were investigated. Under the optimum experiment conditions, the calibration curve was linear in the range of 0.3-5.0 ng/mL and the detection limit was 0.04 ng/mL. The developed method was successfully applied to the extraction and determination of rhodium in water samples and rhodium carbon catalyst.Part three:cloud point extraction (CPE) in combination with laser thermal lens spectrometry (LTLS) has been developed for the preconcentration and determination of palladium. Palladium was complexed with 2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminoaniline as a complexing agent in an aqueous medium and concentrated by octylphenoxypolyethoxyethanol as a surfactant. Factors affecting cloud point extraction were evaluated and optimized. The interference effect of some cations and anions was also studied. Under the optimum experiment conditions, the calibration curve was linear in the range of 0.4-6.0 ng/mL and the detection limit was 0.04 ng/mL. After optimization of the CPE conditions, the presented preconcentration procedure was applied to the determination of palladium in water samples and palladium molecular sieve.Part four:a cloud point extraction (CPE) procedure has been developed for the determination trace amounts of cobalt by using laser thermal lens spectrometry (LTLS). Complex of cobalt with 2-(5-bromo-2-pyridylazo)-5-dimethylaminoaniline (5-Br-PADMA) were extracted into the surfactant-rich phase of octylphenoxypolyethoxyethanol from samples. The concentration of chelating agent and surfactant, pH, equilibration temperature and time was optimized. At optimum conditions, the calibration curve was linear in the range of 0.4～6.0 ng/mL and the detection limit was 0.05 ng/mL. The method has been applied to determination of cobalt in VB12 with satisfactory results. |
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