Preparation Of Monolithic Solid Phase Microextraction Phases For Sample Pretreatment Combined With Electrosorption Technology

Solid phase microextraction （SPME） is a novel sample preparation technique based on solidphase extraction （SPE）. SPME can be characterized as a simple, fast, solvent-free （or using a smallamount of solvent） and stabilized method. Commercial SPME devices and reported SPMEresearch works mainly use the coating type extraction medium, which is adverse to improveextraction capacity and sensitivity, due to the thinner extraction volume. Monolithic organicpolymer adsorption materials have thicker extraction volume and rich interconnected pores, widelyused as the stationary phase in the separation technique. In this research, monolithic adsorptionmaterials were used as extraction phase instead of the coating phase; electric field was introducedto shorten the extraction time and improve the extraction capacity.Chapter2established a novel method of SPME-HPLC for determing DES in food, by usingcommercial PA fiber extraction phase and homemade extraction-desorption device. Theexperimental conditions were optimized, including extraction time, desorption time, ionic strength,et al. Under the selected conditions, this method showed a good linear relationship in the range of0.02².0μg/mL. Detection limit and coefficient of variation were0.006μg/mL and3.82%,respectively. The recoveries of spiked DES in food samples were higher than80%.In Chapter3, epoxy resin based polymer monoliths were prepared and applied to extract Co²⁺in water as extraction medium of in-tube SPME, coupled with flow injection and ICP-AESdetermination. Under the optimized conditions （extraction flow, extraction time, solvent pH, etc.）,the method showed a good linear relationship in the range of0.1³.0μg/mL, with a correlationcoefficient of0.9993. The detection limit （S/N=3） and the coefficient of variation were0.03μg/mLand4.8%, respectively. Compared with direct injection, an enrichment factor was3. The recoverieswere more than85%.In order to enhance the extraction capacity and shorten the extraction time, a novel epoxy resinbased polymer monolithic micro-column extraction was successfully developed by imposingelectric field. The experimental conditions including electric potential, extraction and desorption time, ion strength and solvent pH were investigated and optimized. The extraction capacity andextraction rate of cresol red could be strongly enhanced by anodic polarization, while cathodalpolarization had less effect on the adsorption of cresol red. The equilibrium extraction capacity ofon the self-made system was four times higher at+300V, in comparison with the absence ofelectric field. The kinetic equilibria could be explained as Lagergren first-order. The electrosorptionisotherm of cresol red on nonconductive polymer micro-column was in good agreement withFreundlich and Linear equations.In chapter5, the epoxy resin-based polymer membrane was made as extraction phase forenriching nitrobenzene in water samples, increasing the contact area to improve extraction rate.Electric field was introduced to further improve the membrane extraction capacity and extractionrate. The main extraction conditions were investigated combined with HPLC, including electricpotential, extraction time, solution pH and ion strength, etc. The results showed that cathodalpolarization enhanced significantly extraction capacity. The method presented a good linearityrelationship in the range of0.05³.0μg/mL, with a correlation coefficient of0.9929. The lowdetection limit （S/N=3） was0.015μg/mL, and the coefficient of variation was4.3%. Therecoveries of nitrobenzene by the standard addition method ranged from79.8%¹08.2%.For further discussing the effect of electric field on extraction process, Chapter6mainlyconcerned the different models of the imposed electric field. Monolithic organic-inorganic hybridC-SiO₂porous material was prepared as extraction matix, and the Co²⁺in water was selected asmodel target analyte, the extraction recoceries were investigated by applying different electric fieldmodels. The results showed that: alternating current voltammetry and square wave voltammetrycould strongly enhance the adsorption capacity of Co²⁺by cathodal polarization, whilepotentiostatic method and normal pulse polarography had no significant enhancement effect onadsorption capacity. The solution pH5⁶enhanced electrosorption. Potentiostatic method, normalpulse polarography and controlled-current techniques are suitable for adsorbing Co²⁺in low saltsolution, while square wave voltammetry is suitable for removing Co²⁺in high salt solution. Thedesorption rate of five electric field models were more than60%.