Synthesis and evaluation of polymer based zwitterionic stationary phases for separation of tonic species

Three different zwitterionic functional stationary phases for chromatograph y were synthesized on the basis of 2-hydroxyethyl methacrylate (HEMA) polym eric particles. Two synthesis routes? producing materials designated S300-E CH-DMA-PS or S300-TC-DMA-PS, involved activation of the hydroxyl groups of the HEMA material with epichlorohydrin or thionyl chloride, respectively, f ollowed by dimethylamination and quaternizing 3-sulfopropylation with 1,3-p ropane sultone, The third route was accomplished by attaching methacrylate moieties to the HEMA through a reaction with methacrylic anhydride, followe d by graft photopolymerization of the zwitterionic monomer 3-[N,N-dimethyl- N(methacryloyloxyethyl)ammonium] propanesulfonate, initiated by benzoin met hyl ether under 365-nm light. According to elemental analyses, both the S30 0-ECH-DMA-PS and S300-TC-DMA-PS materials appeared to have overall charge s toichometries close to unity, whereas the grafted material, S300-MAA-SPE, s eemed to carry an excess cf anion exchange sites in addition to the zwitter ionic groups. Yet all three zwitterionic stationary phases were capable of separating inorganic anions and cations simultaneously and independently us ing aqueous solutions of perchloric acid or perchlorate salts as eluent, al beit with markedly different selectivities. On the S300-TC-DMA-PS and S300- MAA-SPE materials, tire retention times increased for cations and decreased for anions with increasing eluent concentration, whereas with the S300-ECH -DMA-PS material, the retention times of both anions and cations decreased with increasing eluent concentration, These results demonstrate the importa nce of choosing appropriate synthesis conditions in order to prepare covale ntly bonded zwitterionic separation materials with an acceptable charge bal ance.