Construction And Application Of New Liquid Chromatography Stationary Phase Based On Dendritic Organic Molecular Gel Agents

As a separation technique,HPLC plays an irreplaceable role in separation science and is one of the most widely used techniques in the fields of environmental monitoring,food safety and pharmaceutical analysis.Significant progress has been made in the field of analytical science since the 1970s,and this progress has been largely dependent on the development of new stationary phases.The stationary phase,the heart of chromatography,is a prerequisite for the effective detection of the target analytes.The selectivity and efficiency of the separation depends to a large extent on the stationary phase used.Therefore,the innovative development of new stationary phase polymers with high separation efficiency,flexible selectivity and a wide range of applications has been one of the research priorities in the field of analytical science.In recent years,dendritic organic molecular gels have attracted a lot of interest due to their clear structure,structural tunability and ability to form a variety of non-covalent interactions.In order to further develop the potential applications of dendritic organic molecular gels,three different structures of dendritic organic molecular gel materials were prepared and applied to chromatographic stationary phases and solid phase extraction,and their separation and enrichment properties were investigated in this thesis.The study and main results are as follows:(1)Dendritic organic molecular gels are a promising class of three-dimensional network compounds.In this work,the third generation of organic molecular gel G3 was synthesized with benzyl alcohol as raw material and dimethyl 5-hydroxy-m-phthalate as growth unit.A novel dendritic modified stationary phase(SiO2-G3)of organic molecular gel was synthesized by grafting cyanogen chloride(CC)onto silica(5μm)surface.The developed stationary phase not only exhibits high molecular shape selectivity but also has RPLC/HILIC/IEC mixed-mode properties in HPLC due to its ordered structure,a variety of strong ππ stacking interactions and the introduction of a hydrophilic triazine fraction during the grafting process.The developed columns exhibit flexible selectivity,enhanced separation performance and better separation of monosubstituted benzene,polycyclic aromatic hydrocarbons(PAHs),positional isomers,nucleotides and nucleobases,benzoic acid and aniline compounds compared to commercial C18 columns.In addition,the new column can achieve baseline separation of PAH contaminants in Yellow River water,validating its potential for application in real sample analysis.(2)The SiO2-G3’ enrichment material was prepared as a solid phase extraction sorbent for PAHs by modifying SiO2(45μm)in the same way using the dendritic organic molecular gelant G3 from(1).The adsorption performance of SiO2-G3’ on PAHs(naphthalene,biphenyl,phenanthrene,fluoranthene and pyrene)and its adsorption mechanism were investigated.The results showed that SiO2-G3’ had good adsorption capacity for the five PAHs with maximum adsorption amounts of 4.20 μg mL-1,4.33 μg mL1,4.56 μg mL-1,4.79 μg mL-1 and 5.46 μg mL-1,respectively.The fitted sorption kinetics and sorption isotherm studies indicate that the SiO2-G3’ solid phase extraction sorbent is chemisorbed as a single molecular layer.In addition,SiO2-G3’ has good reusability,with adsorption rates still above 76%after 5 consecutive cycles,indicating that it is a promising adoretical for the separation and enrichment of PAHs.(3)Synthesis of a symmetrical discoidal dendritic organic molecular gel(GSDM)based on 4octyloxybenzoic acid and 1,3,5-tris(4-aminophenyl)benzene.The GSDM was bonded to the SiO2 surface to prepare a symmetrical discoidal dendrimer modified stationary phase(SiO2@GSDM).The material was characterized by SEM,elemental analysis,FT-IR and TGA.A variety of shape restricted isomers such as polycyclic aromatic hydrocarbons and tocopherols were separated in reversed phase high performance liquid chromatography mode.The separation capacity and molecular shape selectivity of the prepared stationary phase were evaluated by separating the PAHs isomers and the standard SRM 869b and compared with a commercial C18 column.The results showed that the stationary phase exhibited better separation of the shape isomers such as o-terphenyl,p-terphenyl,terphenyl and tocopherol isomers.Since symmetrical discoidal dendritic organic molecular gels are semi-flexible and rigid,the SiO2@GSDM stationary phase interacts with the solute several times to achieve an efficient separation of multiple compounds.In addition,the SiO2@GSDM stationary phase contains long alkyl chains and aromatic rings,which makes the stationary phase suitable for confining the analytes in their voids(cavities)to improve separation selectivity.Thus,the SiO2@GSDM stationary phase is highly molecularly shape-selective,allowing for the effective separation of shape isomers.(4)An o-phenylenediamine-derived dendrimer organic molecular gelant was synthesized and immobilized on silica to form an o-phenylenediamine-derived dendrimer organic molecular gelant grafted porous SiO2 stationary phase(SiO2@G1).Due to the introduction of the benzimidazole group and two long alkyl chains in the modifier,the modified stationary phase exhibits amphiphilic characteristics and the organic molecular gel contains several interaction sites inside the gel such as amide groups,hydrogen bonding,π-π stacking,electrostatic interactions and hydrophobic interactions,which provide good molecular recognition.The separation behaviour of SiO2@G1 as a chromatographic stationary phase was investigated by high performance liquid chromatography.The results show that this dendrimer organic molecular gelant-modified organic molecular gel phase not only exhibits strong shape selectivity for PAHs and β-carotene(shape-restricted isomers)in RPLC,but also separates polar nucleosides and nucleobases,anilines and benzoic acids in HILIC mode and achieves high separation efficiency.The enhanced recognition of PAHs and biomolecules by SiO2@G1 is achieved by its formation of multiple interaction sites with the highly ordered gel structure.The results show that the dendritic organic molecular gel system derived from o-phenylenediamine is assembled on the carrier particles,and the form-restricted isomers such as tocopherol,beta-carotene and PAHs can form hydrogen bonding,π-πpacking,electrostatic and hydrophobic interactions with the gel system.The comprehensive effect of these weak interaction centers allows the efficient separation of the shape isomers.