Sampling Of Dissolved Orthophosphate And Ammonium By The Diffusive Gradient In Thin Films Technique(DGT)

Water eutrophication has become a worldwide environmental problem in recent years.The concentration of dissolved orthophosphate and ammonium can directly lead to water eutrophication.Thus,it is necessary to investigate a simple and reliable tool to sample dissolved orthophosphate and ammonium.The diffusive gradient in thin film technique(DGT)is an in-situ passive,continuous sampling method and is an effective supplement for active sampling method.For its easy operation and flexibility,DGT technique was widely applied in waters,soils and sediments for sampling labile metal ion,inorganic anion and bio-availability.This dissertation established methodology of sampling of dissolved orthophosphate and ammonium by DGT technique.The major results and contents of this thesis are as follows:1.A method of sampling dissolved orthophosphate by DGT technique was established,using nitrocellulose membrane as the protecting filter,polyacrylamide gel as the diffusive phase and the PIP-gel as the binding gel.The morphology and structure of the PIP-binding gel was characterized by SEM and FT-IR.The adsorption character of PIP gels for phosphate was investigated.The validity of PIP-DGT,effect of pH,ionic strength and biofilm on the PIP-DGT performance was investigated.The results indicate that the adsorption of phosphate by PIP-gels conformed to pseudo-second order kinetic model and Langmuir isothermal model.PIP-gels had various adsorption sites and mainly presented heterogeneous phase adsorption.Sampling of phosphate using PIP-DGT was consistent over the pH 3 to 9 range and the 1×10-8 to 0.01 mol·L-1 ionic strength range.Linear relationship was obtained with time to accumulated mass of phosphate on the binding phase.PIP-DGT can realize long-term application and show selectivity for phosphate.The biofilm formed on the surface of DGT can hinder the analyte and decrease the diffusion coefficient which was linearly decreased with the thickness of biofilm.2.A method of sampling ammonium by DGT technique was established,using nitrocellulose membrane as the protecting filter,polyacrylamide gel as the diffusive phase and the zeolite gel as the binding gel.The adsorption character of zeolite gels for ammonium was investigated.The diffusion coefficient of ammonium in the polyacrylamide gel was measured by the diffusive cell.The validity of zeolite-DGT,effect of pH,ionic strength and other ions on the zeolite-DGT performance and application of DGT in fresh waters and soils were investigated.The method was validated by studying the uptake of ammonium ion from in freshwaters by zeolite gels which was found to be fast enough to meet the requirements of DGT.The concentrations determined via DGT agreed well with the concentrations determined in bulk solutions.Sampling of ammonium ion using zeolite-DGT was consistent over the pH 3 to 8 range and the 0.001 to 10 mmol L-1 ionic strength range.The method also performs predictably in natural waters and agricultural soils containing various metal ions.The technique is considered to be a viable passive tool for sampling ammonium.3.A novel selective hybrid cation exchanger material(Cu-HCIX)was prepared by dispersed sub-micro cupric oxide particles in cation exchange resin D61.The HCIX binding gel was prepared by mingling with polyacrylamide gel solution and Cu-HCIX resin powder.Sampling method for ammonium by DGT technique was established,using nitrocellulose membrane as the protecting filter,polyacrylamide gel as the diffusive phase and the HCIX-gel as the binding gel.The morphology and structure of the Cu-HCIX was characterized by SEM and FT-IR.The static and dynamic adsorption character of Cu-HCIX for ammonium was investigated.The validity of HCIX-DGT,effect of pH,ionic strength and biofilm on the HCIX-DGT performance was investigated.The results indicate that the static adsorption of ammonium by Cu-HCIX conformed to pseudo-second order kinetic model and Freundlich isothermal model.Compared to D61 resin,the adsorption capacity and selectivity of Cu-HCIX resin was greatly enhanced when in fixed-bed column runs passing with low-concentration ammonium solution.Sampling of ammonium ion using HCIX-DGT was consistent over the pH 6 to 8 range and the 1×10-6 to 0.1 mol·L-1 ionic strength range.Linear relationship was obtained with time to accumulated mass of ammonium on the binding phase.The method also performs predictably in natural waters containing various metal ions.In conclusion,The DGT technique is considered to be a viable passive tool for sampling dissolved orthophosphate and ammonium.