Derivization-Cloud Point Extraction Of Isoniazid And Pesticides Residues And Determination Of Melamine Of Oscillopolarography

The thesis includes two parts:Part I:The application of derivization in cloud point extraction of isoniazid, organophosphorus and N-methylcarbamate pesticidesIn order to enhance sensitivity, sample pretreatment is requisite for matrix samples. Compared to traditional extraction method, cloud point extraction (CPE) has been introduced as a promising new separation and extraction technique, as an alternative to toxic organic solvents. The technique is effective for extracting solute, especially hydrophobic solute. However, there are two limitations for CPE:compounds with strong polar can not be extracted efficiency and the intense absorption of surfactant in UV region would interferer the detection using high performance liquid chromatography (HPLC)-UVD.Isoniazid has played an important role in the treatment of tuberculosis. However, the hydrophility of isoniazid is so powerful that the micelles have not sufficient ability to solubilize or enrich isoniazid moleculars. In this paper, the problem was overcome by a reaction of isoniazid and p-dimethylaminobenzaldehyde to give isonicotinyl hydrazone with weak polar. Langmuir isotherm was developed to quantify the amounts of surfactant required in isoniazid and isonicotinylhydrazone systems, respectively. According to the calculated results, only in PEG4000system can isonicotinyl hydrazone be efficiently extracted.The evaluation of trace levels of pesticides in agricultural products and other samples is nowadays a priority objective to ensure food quality and to protect environment. In this work, eight organophosphorus and N-methylcarbamate pesticides reacted with4-aminoantipyrene to form intensely colored compounds. After derivization, the detection wavelength was shift from230nm to500nm. Therefore, the surfactant would not interferer the detection. Thus, a new derivization-cloud point extraction-HPLC method was proposed for the determination of eight pesticides. The method was applied to determine the eight pesticides in the corn samples, the limits of detection were1×10-4to1×10-3mg kg-1, with recoveries ranged between80.8%and102%, at the spiking levels of5×10-3,2×10-2and0.2mg kg-1, respectively. The limit of determination were1×10-4～1×10-3mg kg-1.Part II:Rapid determination of melamine by OscillopolarographyThe intoxication accidents related to melamine emerge in endlessly in recent years. For this reason, the detection of melamine has raised much concern. In this paper, we studied the methods for dispelling the interference of colloidal protein in milk. Polarography method was proposed for the determination of melamine in milk, based on the polarographic wave of melamine in an alkaline solution. The peak current of this method was linearly proportional to the melamine concentration in the range of0.4-10.0mg kg-lwith the detection limit of0.1mg kg-1. The recovery was between78.2%～92.5%. The whole determination procedure could be completed in20min.