| Ion-exchange stationary phases with functional groups covalently bonded have receivedmore and more attention because of their better stability. The stationary phases can beobtained through two methods. One is by direct co-polymerization of the monomers withzewitterionic ion-exchange functionality and crosslinker, and the other is by modification ofsilica monolith surface with zewitterionic functional groups. The latter method is not onlycomplicated, but also prepared monolithic columns are used only between pH2~8. Organicpolymeric monoliths can be prepared simply and is suitable for a wide range of pH values.However, organic polymeric monoliths suffer from swelling/shrinking in the mobile phases ofdifferent compositins, thus leading to many adverse effects on separation.In order to overcome the adverse effects of organic polymeric monoliths, a zwitterionicmonolith was prepared by in-situ polymerization of methacrylic acid and2-(dimethyl amino)ethyl methacrylate in a250μm i.d. fused silica capillary pre-packed with silicamicro-particles. The optimal conditions for preparation of the column were established byoptimizing the total concentration of the monomers, the composition of porogens and thetime of polymerization. The optimized concentration, composition of the porogens and thetime of polymerization are T=25%(C=30%),8:1:1and5h, respectively. The preparedcolumn was evaluated in terms of micro-pore structure, endurance of pressure, permeability,ability of anti-swelling, ion-exchange capacity and column efficiency. Finally, the conditionsfor separation were investigated and the effects of the pH value and composition of mobilephase were examined through the separation of a group of inorganic anions and organicamine cations. Under the optimal separation conditions, the4cm long monolithic columnwas successfully used to fast baseline separate4inorganic anions in6min and3organicamine caions in9min. |
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