Application Of Liquid Phase Microextraction In Pesticides And Pollutant Residues Analysis

With the continuous development of modern society and the continuous improvement of people’s living standard, the pollutions of agricultural products and environment caused by various factors has received considerable attentions. Pesticide residue detection and pollutant residue detection is an essential step in the safety regulation of agricultural products and environment. It is particularly important to establish reliable, effective, and sensitive residue detection methods to comply with the new situation and requirements, which lead to a fast development of sample preparation techniques. In recent years, liquid-phase microextraction (LPME) becomes one of the most popular and attractive sample preparation methods because of its simplicity, effectiveness, and environmental friendly. Although LPME have been established and developed for approximately twenty years, some deficiencies still exist in different processes. Based on the deficiencies of some LPME approaches in existence, this dissertation introduces and implements some novel or improved methods, which are presented as follows:Combining directly suspended droplet microextraction (DSDME) and solidification of the floating organic solvent technique (SFO), a directly suspended-solidified floating organic droplet microextraction (DS-SFO) method was developed. DS-SFO combined with HPLC-DAD was applied for the preconcentration and determination of four fungicides (i.e., chlorothalonil, triadimefon, cyprodinil, and trifloxystrobin) from water and honey samples. In this method, no special devices or supporting materials are required. The extraction phase can be easily collected by means of solidification of the droplet after the extraction step. The experimental parameters affecting the extraction efficiency were investigated and optimized. Under the optimized conditions, this method performed extraction recoveries of80%to93%and limits of detection (LOD) of0.20to1.95μg L-1for water samples, and extraction recoveries of70%to83%and LOD of1.14to11.06μg kg-1for honey samples.A type of ultrasound-assisted emulsification microextraction (USAEME), named slow-injection USAEME (SI-USAEME) was developed. In the technique, the extraction solvent was injected into the aqueous sample which being ultrasonicated. The simultaneous injection of extractant and ultrasonication of sample results in an good emulsification and efficient extraction,(i) SI-USAEME based on organic extraction solvent combined with HPLC-VWD analysis was applied for the analysis of four phthalate esters (i.e., dimethyl phthalate, diethyl phthalate, dibutyl phthalate and benzyl butyl phthalate) in water samples. The experimental parameters were analyzed and optimized through a central composite face-centered design. Under the optimized conditions, this method performed extraction recoveries of75%to87%and LOD of0.26to1.46μg L-1for water samples,(ii) SI-USAEME based on aqueous extraction solvent combined with UPLC-MS/MS analysis was applied for the determination of deoxynivalenol (DON) and its metabolite, de-epoxy-deoxynivalenol (DOM-1), in maize and pork samples. A comparative study between the SI-USAEME, the immunoaffinity column (IAC) cleanup method, and the solid-phase extraction (SPE) cleanup method was presented. Results showed that the method recoveries ranged from73to85%, and LODs ranged between4.2and6.2μg kg-1for DON and DOM-1, respectively. No significant differences were obtained between the results of studied three methods for the analysis of real samples.An ionic liquid-based in situ dispersive liquid-liquid microextraction (IL-based in situ DLLME) was developed. The analytes were extracted into IL extractant which was formed through the reaction between water-soluble IL and lithium bis[(trifluoromethane)sulfonyl]imide (LiNTf2).(i) IL-based in situ DLLME combined HPLC-VWD analysis was applied for the analysis of four insecticides (i.e., methoxyfenozide, tetrachlorvinphos, thiamethoxam, and diafenthiuron) in environmental water samples. Under the optimized conditions, the method performed extraction recoveries of82%to102%and LOD of0.98to2.54μg L-1.(ii) Combining IL-based in situ DLLME with ultrasound-assisted DLLME into one extraction procedure, a novel sequential DLLME was developed for the determination of four aryloxyphenoxy-propionate herbicides (i.e., haloxyfop-R-methyl, cyhalofop-butyl, fenoxaprop-P-ethyl, and fluazifop-P-butyl) in environmental aqueous samples. Under the optimized conditions, the proposed method performed extraction recoveries of78%to91%and LOD of1.50to6.12μg L-1,which was better than widely used DLLME procedures.A novel concept about automated DLLME is put forward. Automation of the IL-based in situ DLLME is realized using a fully automatic SPE workstation, SPE columns packed with nonwoven polypropylene (NWPP) fiber, and a modified operation program. DLLME procedures including the collection of water sample, injection of the ion exchange solvent, phase separation, elution of the retained extraction phase, and transfer of the eluent into vials, can be performed automatically. Automated IL-based in situ DLLME combined HPLC-DAD analysis was applied for the analysis of benzoylurea insecticides (i.e., diflubenzuron, teflubenzuron, flufenoxuron, and chlorfluazuron) in water samples. Under the optimized conditions, the method achieved extraction recoveries of80%to89%and LOD of0.16to0.45μgL-1.