Cloud Point Extraction And Its Application To Determination Of Pesticde Residues

The first step of pesticides residue analysis is to extract and refine the sample of trace pesticides, which affects on the accuracy of results directly. The common methods require a analyzing sample with higher purity. The complicated matrixes can interfere with the retention analyses and damage the instruments. Obtaining, concentrating and purificating the sample are the most important preparation steps in the retention analyses of pesticides. Cloud point extraction (CPE) is one of the new environmentally benign liquid-liquid extraction method, which 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. The micellar solution above separates into a surfactant-rich phase of a small volume and a dilute 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 surfactant-rich phase. 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.The purpose of this thesis is to set up a method to enrich trace organphoshate pesticide by cloud point extration. Six nonionic surfactants were compared about the cloud point, ability of enrichment and phase separation. In fact, we can change the cloud point of C₁₂E₁₀ through adding Na₂SO₄ to this system, which is good at solubilization. C₁₂E₁₀ appears viscosity solid after phase separation. The cloud point of TX-114 is 23°C. Because of the bigger density, TX-114 is under the system after phase separation, then inverse the tube to get coacervate phase. While C₁₂E4 has a similar density to water, so it is difficult to separate the two phase. C18E₁₀, C₁₂E23 and TX-100(Na₂SO₄) system is aslo unsuitable to apply cloud point extraction owing to the fluid of coacervate phase that disturb the veracity and repetition of extraction work.Choosing parathion-methy1 as extracted compound. The dependence of extraction efficiency on the initial surfactant concentration, temperature, the concentration of Na₂SO₄ and phase separation condition were investigated. The extraction can reach 90.29%, when using 5 g·L-1 C₁₂E₁₀ and 120 g·L-1 Na₂SO₄ at 35°C. While the extraction can reach 85%, when using 20 g·L-1 TX-114 at 35°C. Compare the two system above, C₁₂E₁₀- Na₂SO₄ has a series of merit, such as small surfactant volume, large enrichment multiple, rapid phase separation and easy to analyse by High performance Liquid Chromatography.In the actual system experiment, organophsphate pesticide at three level concentrations was added in cabbage. It is resonable to detect pesticde residues by combining cloud point extraction with high performance liquid chromatography, and the method detect limit (MDL) for parathion-methy1, parathion and phoxime can reach 0.0008 mg/kg, which is under the country standard (0.01mg/kg).