Design,preparation And Application Of Novel Polymer-based Ion Exchangers For Ion Chromatography

Ion exchangers are particulate materials which are superficially functionalized with single or multiple ion exchange groups by means of covalent bonding,non-covalent adsorption or grafting.They are normally used for the enrichment and separation of ionic compounds.Ion exchangers are playing a very critical role in the chromatographic performance when they are utilized as the packing material of ion exchange columns,the core unit of ion chromatography(IC).With the development of food,pharmaceutical and environmental industries,IC has become increasingly needed for the past few years.Hence,the design and invention of new ion exchangers with higher efficiency and better selectivity is practically significant for meeting the growing complexity of the analytes.In this paper,we have developed new techniques of coating of graphene materials and thiol-ene click modification,to fabricate a series of novel ion exchangers.The proposed ion exchangers were used for the separation of a number of ionic compounds.Their chromatographic performance for IC was thus systematically investigated.In Chapter 1,different types of ion exchangers,to refer in particular to stationary phases for IC,were introduced in terms of constructional principles,fabrication technics and chromatographic properties.Additionally,several newly developed ion exchangers were specifically elaborated according to the current trends of IC technology.In Chapter 2,a facile evaporation-reduction method was introduced for the hydrophilic coating of graphene sheets onto 6.0 μm PolyStyrene/Divinylbenzene particles.These particles with graphene coating were proven appropriate substrates for further step-growth hyperbranching modification to make pellicular anion exchangers.By means of varied characterizations,the successful coatings of graphene and hyperbranched condensation polymers were analyzed and verified.The chromatographic performance was also demonstrated with IC.In Chapter 3,cysteamine and cysteine moieties were covalently immobilized onto 5.8 μm Allylmethacrylate/Divinylbenzene and 7.0 μm Ethylvinylbenzene/Divinylbenzene particles via neat thiol-ene modification.The obtained aminated polymer-based microspheres were converted into polymer grafted anion exchangers via further step-growth hyperbranching modification.The anion exchangers demonstrated good separation and dependable durability for suppressed anion exchange chromatography.In the case of a 3-layered anion exchanger,simultaneous separation of nine model anions was achieved by isocratic elution in 17 min with efficiencies up to 16,100 N/m.In Chapter 4,a one-step method to fabricate linear polyquaternary ammonium anion exchangers was developed on the basis of thiol-click modification.The anion exchangers were prepared from aminated 4.6 μm Ethylvinylbenzene/Divinylbenzene particles via facile epoxy-amine polymerization.In separation of various anionic compounds,the newly developed anion exchangers showed high efficiency(e.g.,>30,000 N/m for chloride)and peculiar chromatographic behavior as compared to previously reported hyperbranched phases.Experimental results showed that the choice of the amine reagent had a significant impact on the selectivity,which in our opinion is associated with charge density,hydrophilicity and low cross-linking of the functionalities.In Chapter 5,on the basis of thiol-click modification,novel cation exchangers were fabricated from 4.6μm Ethylvinylbenzene/Divinylbenzene particles via thiol-radical-mediated polymerization using acrylic acid and maleic anhydride as the monomers and sodium 2-mercaptoethanesulfonate as the modifier.The cation exchangers were bifunctional with both carboxylic and sulfonic groups,and were able to achieve the baseline-resolved separation of typical cations with simple strong acid eluents.The retention behavior of metal cations and organic amines was investigated by different chromatographic models.The good performance of the cation exchangers was demonstrated by the separation of ten cations within 24 min in gradient mode.