Synthesis Of Molecularly Imprinted Wax And Its Application On Environmental Sanitation Monitoring

Environmental sanitation monitoring is of great significance for reflecting the current situation of environmental health and carrying out prevention and control measures.Sample pretreatment is an important process in environmental sanitation monitoring,which is not only time-consuming,but also the main source of analysis error.Compared with traditional solid-phase extraction which was tedious and time-consuming,this study proposed an elution-free extraction method based on molecularly imprinted wax,which had the merits of simpler operation,less steps,as well as lower solvent consumptions,and realized the rapid analysis of pollutants in different samples.Part 1 Synthesis of wax-based molecular imprinting with controllable solid-liquid transition and establishment of elution-free solid phase extractionObjective:This chapter mainly focused on the combination of wax and molecular imprinting technology and the preparation of molecularly imprinted wax(MIW)microspheres.Based on MIW,an elution-free SPE process was established,which was used for the establishment of a rapid analysis method of propranolol by coupling MIW with different fluorescent detectors.The feasibility of wax-based molecular imprinting and elution-free SPE was then verified by a series of experiments.Methods:Wax as the matrix,octadecanoic acid as the functional monomer and propranolol as the template were used to synthesize the molecularly imprinted wax with selective adsorption capacity towards propranolol.Due to the reversible phase transition of wax at low temperature,the synthesis process was facile via emulsion method without the need of removing oxygen or purifying the crosslinkers.MIW was characterized by scanning electron microscope(SEM),Fourier transform infrared spectroscopy(FTIR),differential scanning calorimeter(DSC)and thermogravimetric analysis(TGA)for exploring the mechanisms of MIW synthesis.The optimal adsorption conditions of MIW towards the template were investigated simultaneously.Then,the selective adsorption capacity of MIW towards the template was analyzed by adsorption isotherms,adsorption kinetics and selective adsorption experiments.Finally,a rapid analysis of propranolol technology was established by coupling the elution-free SPE process based on MIW with different detectors.Result:SEM,FTIR,TGA and DSC analysis results showed that MIW microspheres were regular spherical structure containing carboxyl,which proved the successful preparation of MIW.The adsorption isotherms results showed that the adsorption of propranolol by MIW and NIW could be described well with the Langmuir adsorption isotherm model.The maximum adsorption capacity of MIW and were 1.44 mg/g and 0.23mg/g,respectively,and the imprint factor was 6.3.The adsorption kinetics showed that the adsorption behavior of MIW and NIW towards the template followed the pseudo-second-order kinetics model,and the initial adsorption rates of MIW and NIW were 0.18 and 0.03 mg/(g·min),respectively.Adsorption selectivity experiments showed that MIW had the highest adsorption capacity for propranolol compared to the other analogs,indicating the selective recognition sites in MIW.On the basis,the rapid propranolol analysis method was established by utilizing the merits of controllable phase transformation of wax.The results of propranolol detection by liquid phase fluorescence displayed a linear range of 0.2-10μg/m L with a linear correlation coefficient R~2 of 0.97and a detection limit of 0.05μg/m L.The results of propranolol detection by solid phase fluorescence displayed a linear range of 0.2-5μg/m L with a linear correlation coefficient R~2 of 0.99 and a detection limit of 0.03μg/m L.Moreover,the relative standard deviation of solid phase fluorescence detection was 1%.Compared with traditional SPE process using MIW spheres,only 1 m L of n-hexane was used to completely recovery the adsorbed PRO from MIW spheres in MIW-based elution-free SPE process,while 20 m L of methanol was consumed in traditional SPE process.Conclusions:In this chapter,MIW microspheres with specific adsorption capacity for PRO were successfully synthesized and applied on the development of elution-free SPE process,which not only greatly reduced the consumptions of organic solvents,but also made the analysis process more convenient.Part 2 Synthesis of porous molecularly imprinted wax and its application on analysis of biological samplesObjective:Based on chapter 1,porous molecularly imprinted wax(p MIW)microspheres with high adsorption capacity and adsorption rate were synthesized,and a method for PRO detection in small volumes of samples based on p MIW was developed.Methods:Based on chapter 1,porous MIW spheres were synthesized by using propranolol as template molecule,wax as the matrix,stearic acid as functional monomers and octadecanol(economical and easy to remove)as porogens.Porous structure in p MIW was characterized by scanning electron microscope,Fourier transform infrared spectroscopy,nuclear magnetic resonance,and specific surface area analysis to explore the corresponding synthesis mechanism and clarify the pore-forming principle of octanol.The synthesis conditions of p MIW spheres were also optimized.Then,selective adsorption capacity of p MIW towards propranolol was investigated by adsorption isotherms,kinetics,and selective adsorption experiments.Finally,a method for the rapid analysis of propranolol in small volumes of samples was established.Result:SEM,FTIR and NMR showed that large numbers of pores were generated in both surface and inner of p MIW spheres after washing with methanol.Specific surface area of p MIW was measured to be 2.4 folds compared to MIW spheres.The adsorption behaviors of p MIW and p NIW towards PRO followed Langmuir isotherms model.According to the Langmuir model,the maximum adsorption amount of p MIW and p NIW towards PRO was 2.44 mg/g and 0.67 mg/g,respectively.Imprinting factor was calculated as 3.6.The adsorption kinetics showed that the adsorption behaviors of p MIW and p NIW towards PRO followed the pseudo-second-order kinetics model.According to the pseudo-second-order kinetics,the initial adsorption rates of p MIW and p NIW were 5.83mg/(g·min)and 2.79 mg/(g·min),respectively.The initial adsorption rates of p MIW were32 times of those of MIW microspheres in chapter 1.The adsorption selectivity experiments showed that p MIW had selective adsorption capacity for propranolol.On this basis,the rapid analysis method of propranolol was established by using p MIW with high adsorption capacity and adsorption rates.The linear range was 0.1-2μg/m L with a LOD(S/N=3)of 0.02μg/m L and a LOQ(S/N=10)of 0.07μg/m L.In the detection of blood and urine samples spiked with PRO,the relative standard deviation of p MIW coupled with fluorescence detection was lower than 10%,and the recovery was higher than 85%,and only 0.1 m L of sample was required for the detection.Conclusions:In this chapter,p MIW microspheres with greatly improved specific surface area and adsorption capacity were synthesized.which were then applied to the rapid detection of PRO in small volumes of blood and urine samples,Part 3 Synthesis of molecularly imprinted wax-based monolithic column and its application on analysis of environmental water samplesObjective:In this chapter,MIW-based monolithic column(MIW-MC)with communicating pores was prepared.In addition,based on MIW-MC,a SPE device was designed to realize the enrichment and analysis of low concentration propranolol in environmental water samples.Methods:By utilizing the affinity of water and Na Cl particles,water was added to enhanced the adhesion of Na Cl particles,resulting in a monolithic salt particle column.The monolithic salt column was then immersed into the precursor solution of molecularly imprinted wax,and vacancy in the monolithic salt column was filled with the wax.After cooling and removing the salt column with water,the molecularly imprinted wax-based monolithic column(MIW-MC)with communicating pores was obtained.MIW-MC was characterized by scanning electron microscopy to observe the porous structure.The adsorption isotherms,kinetics and selectivity were studied to analyze the selective adsorption capacity of MIW-MC towards PRO.The influence of different ions on extraction recovery of MIW-MC was also studied.Coupled with fluorescence detection,MIW-MC was applied on low-concentration PRO detection in environmental water samples.Result:SEM images and other characterization results showed that MIW-MC possessed communicating pores with micro diameters.The results of adsorption isotherms showed that,like the results of MIW and NIW spheres,the adsorption of propranolol on MIW-MC and NIW-MC followed the Langmuir isotherms model.The maximum adsorption of MIW-MC and NIW-MC was 1.49 mg/g and 0.31 mg/g,respectively.Imprinting factor was calculated as 4.8.The adsorption kinetics showed that adsorption of PRO on MIW-MC and NIW-MC followed the pseudo-second-order kinetics model,and the initial adsorption rates of MIW-MC and NIW-MC were 0.72 and 0.22 mg/(g·min),respectively.The results of adsorption selectivity showed that MIW-MC had the most adsorption amounts towards PRO compared with the analogs of PRO.Different ions had no effect on the extraction recovery of PRO by MIW-MC in solution.By coupling with fluorescence detection,MIW-MC was used for the extraction and detection of PRO in sample solutions.the calibration curve of MIW-MC was obtained by detecting the spiked solutions with PRO.The linear correlation coefficient R~2 of the calibration curve was 0.99with a LOD(S/N=3)of 0.03 ng/m L and a LOQ(S/N=10)of 0.1 ng/m L.The relative standard deviation of MIW-MC based fluorescent detection was lower than 10%and the recovery was higher than 90%in different sample solutions.Conclusions:In this chapter,MIW-MC with communicating pores was synthesized,which was then successfully applied on the rapid detection of low-concentration PRO in environmental water samples.