Application Of Supported Liquid Membrane Extraction Techniques In Rapid Detection,Separation And Purification Of Environmental Pollutants

With the development of industrial technology and the improvement of social productivity,the issue of environmental pollution in China is becoming more and more serious,which showed great risk to the human health.Among different environmental pollutants,heavy metal pollutants and drug pollutants aroused the worldwide concern since they were difficult to degrade and easy to bioaccumulate.Currently,the distribution of environmental pollutants has developed from simple trace level distribution to complex multi-levels distribution.Therefore,the implement of efficient separation of pollutants at different levels was of great significance in the fields of environmental monitoring,environmental pollution control as well as resource recycling.Among various separation technologies,liquid-membrane extraction(LME)and electrically assisted liquidmembrane extraction(EME)evolved from supported liquid membrane(SLM)have been widely used in the field of environmental separation and analysis because of their high separation efficiency,excellent purification ability and good stability.However,the current mass transfer study of LME and EME was limited to the investigation of single membrane-based extraction technique at trace or low level,and the mass transfer study and comparison of LME and EME at different levels has not been reported,which greatly limited the further development of aforementioned liquid-membrane based extraction techniques as well as their application in environmental field.Therefore,the current study would conduct a systematic investigation on the mass transfer performances of both LME and EME to improve the mass transfer theories of proposed techniques at different levels.Moreover,based on the analysis of foregoing mass transfer theory,the proposed LME and EME techniques would be applied to rapidly detect the trace level heavy metal ions in biological samples as well as separate and purify high level drug pollutants in complex water samples,respectively.Part 1 Mass transfer study of liquid-membrane extraction and electrically assisted liquid-membrane extractionObjective: LME and EME have become the widespread membrane-based extraction techniques in the separation of environmental pollutants.However,the development and application of LME and EME are limited due to the lack of mass transfer study,especially for the separation of high level compounds.Therefore,the current study would investigate the mass transfer performances of LME and EME with common pollutants to achieve efficient separation of drug contaminants at different levels.Meanwhile,similarities and differences of mass transfer between LME and EME at different levels were also compared,thus providing theory basis for selecting an appropriate membrane-based extraction technique in practical applications(analysis of trace level pollutants or separation and purification of high level pollutants).Methods: In this study,the common drug pollutants including haloperidol(HAL),amitriptyline(AMI),fluoxetine(FLU)and sertraline(SER)were selected as the research objects.By optimizing the extraction conditions,the mass transfer performances of both LME and EME at different levels were systematically investigated,and the similarities and differences of mass transfer performance between them were further compared.Results: The recoveries of LME and EME could reach more than 90% at trace or low level.With the increasing analyte concentration,the recoveries of LME and EME decreased rapidly.At high level,by re-optimizing the extraction conditions,such as extending the extraction time of LME to 180 min and increasing the extraction voltage of EME to 250 V,the sharply decreased recoveries of LME and EME were effectively improved,but the improvement of LME recovery was more obvious.Meanwhile,the average mass transfer rates of each concentration at equilibrium were compared.At trace or low level,the average mass transfer rate of EME was slightly higher than that of LME.For example,when the concentration was 0.5 mg L-1,the difference of mass transfer rate was only 0.069.With the increase of the target analyte concentration,the average mass transfer rate of EME elevated rapidly,while that of LME increased slowly.Moreover,the gap of mass transfer rate between LME and EME was gradually enlarged with the increasing concentration.However,the average mass transfer rate of EME was much higher than that of LME at high level.For example,when the concentration was 200 mg L-1,the difference of mass transfer rate was 9.1.Conclusion: At trace or low level,both LME and EME could achieve high recoveries,and their mass transfer rates were slightly different.However,LME was more convenient and safer than EME since there was no need to introduce the external electric field.Therefore,LME could be used as the preferred technique for the separation of target analytes at trace or low level;At high level,the recoveries of both LME and EME were decreased.Nevertheless,the decreased recoveries could be improved by adjusting the extraction conditions.Meanwhile,the mass transfer rate of EME was much higher than that of LME at high level and EME possessed great advantage of saving time.Consequently,EME could be used as the preferred technique for the separation of high level target analytes from the perspective of separation rate.Part 2 Application of liquid-membrane extraction in rapid detection of trace level heavy metal ions in biological samplesObjective: Development of a rapid and convenient method for the detection of trace level heavy metals in biological samples could effectively rid the dependence of environmental pollution and health research on large-scale analytical instruments in the field of public health,and further improve the level of health assessment and environmental heavy metal pollution monitoring.Fluorescent aptamer beacon(FAB)possessed the advantages of simple operation,fast detection and high sensitivity.Consequently,it has been used to recognize and determine a variety of heavy metal ions in water systems.However,due to its low biostability in biofluids,it was difficult for FAB to be directly applied in analysis of heavy metal ions in complex sample matrices.Therefore,the implement of FABs application in the rapid detection of trace level heavy metal ions in biological samples would greatly promote the improvement of environmental health level in the field of public health.Methods: From the perspective of biological sample preparation,separating trace level metal ion targets into the matrix-free aqueous solution prior to FABs recognition and detection with liquid-membrane based extraction techniques could solve the problem of FABs towards bioanalysis.Based on the conclusion in the first chapter,the current study firstly selected LME to separate the trace level heavy metal targets in biological samples,and then applied FAB to identify and detect the target after separation.Specifically,the previously developed FAB of mercury ion which served as the model beacon was placed into the acceptor phase of LME to build the LME-FAB integrated system.The feasibility of LME-FAB strategy was investigated by exploring the synergistic effect of LME-FAB in addition to compare analytical performances between FAB and LME-FAB.Meanwhile,the practicability of LME-FAB for rapid analysis of trace level heavy metal ions in biological samples was evaluated by urine samples.Results: When the selected model FAB was directly applied to the detection of mercury ion in urine,the low biostability of FAB resulted in the failure detection.Whereas,the LME-FAB could effectively avoid the effect of matrix interference components such as nuclease on the FAB recognition and detection capabilities.In the synergistic effect study,LME protected FAB from the matrix interference,and provided high enriched mercury ions for FAB identification and detection.Meanwhile,FAB could also promoted the extraction of mercury ions based on the principle of extraction kinetics in addition to recognize the target mercury ions.The established LME-FAB method could realize highly sensitive detection of trace level mercury ions in urine samples with a low detection limit of 27 n M.Moreover,the relative recoveries were 96-106% and the relative standard deviations were less than 7% in recovery experiment of real urine samples.Conclusion: In the LME-FAB system,LME and FAB exhibited a synergistic effect in the separation and detection of target compounds.Based on the cooperation of FAB and LME,LME-FAB overcame the challenge of developed FAB towards bioanalysis,and successfully achieved the rapid and convenient detection of trace level mercury ion in urine samples.In addition to the selected model beacon,the success of current LME-FAB integration strategy would greatly utilize the fast and convenient detection advantages of other FABs,thus promoting their application in the detection of trace level heavy metal ions in biological samples,as well as further improving the level of human health assessment and environmental heavy metal pollution monitoring.Part 3 Application of electrically assisted liquid-membrane extraction in the separation and purification of environmental drug pollutantsObjective: The existence of high level drug pollutants in water system not only affected the normal growth of aquatic organisms,but also caused potential harm to human health through biological bioaccumulation.Traditional separation techniques such as liquid-liquid extraction have been widely used in the separation of high content compounds.However,there were some problems such as low separation rate,wasting time and insufficient selectivity.Therefore,it is urgent to develop a separation method with high mass transfer rate and excellent selectivity to achieve the rapid and efficient separation and purification of high level drug pollutants.Methods: EME with high mass transfer rate was chosen to conduct the current study of separation and purification of high level drug pollutants based on the conclusion in chapter one.Firstly,the common drug molecule of propranolol was selected as the research object,and the possibility of efficient separation of high level target compound(propranolol)by EME was investigated by optimizing extraction conditions and developing different flat membrane-based extraction devices.On this basis,the eluents containing high level drug template molecules produced in the synthesis of molecular imprinting was used as a pollutant model to evaluate the practicability of proposed EME technique.Meanwhile,the selectivity of EME separation was investigated by UV-Vis spectra,liquid chromatography and mass spectra.Results: With conventional single-well EME(sEME),the recovery of propranolol at low level was 86%,while it was only 5% at high level.By optimizing the extraction conditions at high level,the recovery just showed a slight improvement.To further improve the extraction efficiency,the high level target was extracted by multi-well EME(m EME)instead of s EME,and recovery was increased to 46%.On the basis of m EME,the current study continued to develop a more convenient and stable larget-volume EME(l EME)and recovery was further increased to 53% with l EME.Therefore,the newly developed l EME was used to separate high level template(propranolol)pollutants produced by different molecular imprinting synthesis methods,and the corresponding separation efficiencies were 57% and 45%,respectively.In addition,with the assistance of UV-Vis spectra,liquid chromatography and mass spectra,it could be observed that there were coexisting interference components in the sample solutions apart from the target substance,while only extractd target analyte existed in corresponding acceptor solutions after EME.Conclusion: In conventional s EME,the recovery of high level target substance was low due to the limited membrane area and the volume of acceptor solution.On the basis of s EME,a convenient and stable l EME device which was constructed by increasing the membrane area and the volume of the acceptor solution could realize the efficient separation of high level targets.On this basis,the practicability of l EME was effectively verified by separating high level drug pollutants in different template eluents.The selectivity of l EME was also confirmed by UV-Vis spectra,liquid chromatography and mass spectra.Overall,the proposed l EME technique achieved the fast,efficient separation and purification of high level drug pollutants in complex water samples based on its excellent separation characteristics.