Determination Of Atrazine And Its Metabolites By Nanofibers Mat Based Solid Phase Extraction Coupled With Liquid Chromatography

This work mainly focused on the development of a novel solid-phase extraction (SPE) system, which was based on a new sorbent of modified nanofibers. Atrazine (ATZ), a kind of triazine herbicides, and its two main metabolites deisopropylatrazine (DIA) and deethylatrazine (DEA) were chosen as the target contaminants. A series of related parameters that may affect the efficiency have been investigated systematically, including the chosen of modified nanofibers, optimization for nanofibers'preparation conditions and SPE operating conditions. The main content of work includes four aspects as follows:1. Preparation and characterization of nanofibersPolyacrylonitrile (PAN) nanofibers mat prepared via electrospinning process was used as the template to fabricate three modified nanofibers mat, polypyrrole-polyacrylonitrile (PPy-PAN) nanofibers mat, hydrazine modified polyacrylonitrile (HM-PAN) nanofibers mat and carboxyl modified polyacrylonitrile (COOH-PAN) nanofibers mat. The morphology of the nanofibers was observed by scanning electron microscopy (SEM), while the compositions of modified nanofibers mat were analyzed with an FT-IR spectrometer. The results of SEM images shown that the average diameters of PAN, PPy-PAN, HM-PAN and COOH-PAN nanofibers were 160nm,280nm,190nm and 180nm,respectively. The surface of PAN nanofibers was smooth, even thickness. However, PPy-PAN nanofibers became coarser with particles on the surface. While the surface of HM-PAN and COOH-PAN showed no significant change when compared with PAN nanofibers. The corresponding characteristic peaks of the functional groups in the FT-IR analysis results indicated that the PAN nanofibers have been successfully modified.2. The screening experiments and the optimal preparation experiment of the nanofibers matThe screening experiments consisted of two parts, static adsorption and dynamic adsorption experiments. The indexes including the time of absorption equilibrium, the adsorption capacity, the adsorption rate for the first 5 minutes, the adsorption capacity for the first 30minutes, the efflux rate of target compounds, were investigated in the screening experiments. There were no significant difference among the four materials for the indexes of the time of absorption equilibrium and the equilibrium adsorption capacity. While in the dynamic adsorption experiments, COOH-PAN nanofibers mat showed the best performance. Therefore, COOH-PAN nanofibers mat was chosen as the adsorbent for the SPE. The preparation conditions were investigated in the following optimization experiments. The mass ratio of PAN and NaOH, reaction temperature and reaction time were investigated based on the indexes of carboxyl content and target recovery. The optimum conditions were established as follows:Dissolve the appropriate amount of NaOH in 150.0mL distilled water with the ratio of 1:30, react for 30 minutes under 90?. Under the optimization conditions, the carboxyl content of COOH-PAN nanofibers mat was about 1mmol/g and the recoveries were all above 80%.3. The optimal experiment of the nanofibers mat based solid phase extractionA series of related parameters that may affect the efficiency, such as the kind of eluent and its volume, the amount of nanofibers mat, ionic strength, pH of the sample, volume of the activator, flow rate of the sample and volume of the sample, have been investigated systematically. Under the optimized conditions, the target compounds in 10 mL water samples can be completely extracted by a 4.0 mg COOH-PAN nanofibers mat and easily eluted by 400 ?L acetonitrile. Around 20 p.L elution was injected directly to HPLC-DAD for determination, without further concentration. Besides, the nanofibers mat could be repeatedly used up to six cycles.4. Establishment and assessment of COOH-PAN nanofibers mat based detection method for DIA, DEA and ATZ in water samplesUnder the optimized conditions, limit of detection (LOD), limit of quantity (LOQ), linearity, precision, recovery were reviewed. The method was applied to detect real water sample, to verify the feasibility. The results were as follow:Under optimized conditions, an excellent linear relationship was obtained in the range of 0.4ng/mL-40.0ng/mL for three target compounds. The LOD for DIA, DEA and ATZ were 0.12ng/mL,0.09ng/mL and 0.09ng/mL respectively. The recoveries ranged from 81.35% to 120.32%, with the intra-day and inter-day relative standard deviations (RSDs) of 4.0%-13.6%(n=5). The proposed method has been applied to the analysis of three target compounds in Taihu Lake water. The results indicated that the concentrations of ATZ were below the limiting value of GB 3838-2002. We also compared COOH-PAN nanofibers mat-based SPE method with National Standard Method of China (HJ 587-2010). Based on the similar recovery, the LOD and LOQ, the organic solvent volume and sample volume for new method were much less than the national standard method, which could shorten the experiment time, reduce the organic solvent volume and save the cost.