Study On Determination And Adsorption Mechanism Of Metsulfuron-methyl In Minerals And Soils

In this thesis, adsorption-desorption behaviour of metsulfuron-methyl was studied in five minerals and four soils using batch equilibrium experiments. Adsorption capabilities among those minerals and soils were compared, the main factors influencing adsorption and mechanisms contributing to adsorption were proposed. the main results were summarized as follows: 1. Borate buffer was used to separate metsulfuron-methyl herbicide by Capillary Electrophoresis (CE). Under the experimental conditions, the magnitude of electric current was 19.8 u A and relatively stable. Transition time was about 4.6 mm. 2. Using external standard method, the working curve of the peak area and the content of standard sample was Y (peak area) 0.01 28X (concentration), R2= 0.9997. 3. Metsulfuron-methyl solution was analyzed by both CE and High Performance liquid chromatography (HPLC), and the result was consistent. The correlation of the results by the two methods was Y= 1.0026X + 0.0371, R2= 0.9992. 4. Adsorption isotherms fitted Freundlich equation (Cs KtQe~~) well. The adsorption coefficient Kf was in the order: Al3~-montmori1lonite (57.80) > Cu2~-montmorillonite (17.40)> Ca2~-montmori1lonite (3.77)> kaolinite (0.81) > goethite (0.70). The amount of metsulfuron-methyl adsorbed by kaolinite and goethite was less than that of homoionic montmorillonite, which may be due to the different adsorption mechanisms of the two types of minerals. The 67 main interaction type between metsulfuron-methyl and kaolinite and goethite was physical adsorption, while homoionic montmorillonite was combined with metsulfuron-methyl through cation bridge. 5. The adsorption ability of metsulfuron-methyl by minerals followed the order: Al3~-montmorillonite > Cu2~-montmorillonite > Ca2~-montmori1lonite, indicating that the type of ion was very important in the adsorption of metsulfuron-methyl. The ion potential (z/r) of Al3~, Cu2~, Ca2~ was 3/51, 2/72 and 2/99 (pm?, respectively. With ion potential of the cation increasing, the adsorbed amount of metsulfuron-methyl by cation exchanged montmorillonite increased. 6. Metsulfuron-methyl adsorption on minerals was found to be closely related to the pH value of mineral suspension. Adsorption greatly decreased with pH increase of mineral suspension. 7. Adsorption on four soils could be described both by linear adsorption model and Freundlich equation, suggesting that hydrophobic partition was an important mechanism accounting for persistence of metsulfuron-methyl in soils. 8. A regression model between soil pH and linear adsorption coefficient was developed: Kd 25.86?4.60 pH. The linear adsorption coefficient of metsulfuron-methyl in soils was negatively correlated with pH value, and the effect of pH values on adsorption was significant.