The investigation of ion-exchange properties of novel zwitterionic and amphoteric stationary phases and their application to the separation of inorganic and organic ions
Nesterenko, Ekaterina Pavlovna (2008) The investigation of ion-exchange properties of novel zwitterionic and amphoteric stationary phases and their application to the separation of inorganic and organic ions. PhD thesis, Dublin City University.
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Over recent years development of ion chromatography (IC) has focused on new phase technologies to s~multaneously increase efficlency and vary selectivity. To increase selectlvlty it IS necessary to develop new selective ]on-exchangers by varying the nature of functional groups and the matrix of the statlonary phase. Zwittenonic ioncxchangcrs, where positlve and negatlve charges are located in close proxlmlty, exhibit potentla1 for selectivity optlm~sationin IC due to vanation of the ratio of electrostatic attract~onlrepulsion forces between analyte ions and ion-exchange groups. The main advantage of zwitterionic ion-exchangers is the possibility of their use for the simultaneous separation of catlons and anlons and the use of diluted elucnts, which significantly increases the sensltlvlty of detection and can contribute to the increased efficlency.
Here various reversed-phase sorbents dynamically coated wlth N-(dodecyl-N,Nd~methylammonio)alcanoates were produced and charactensed. The ion-exchange properties of these new phases were investigated and the retention mechanism of Ions on these stationary phases elucidated. From investigations into the effect of pH, concentration, nature and charge of the eluent catlon on the retention of anions, it was shown that separation of anions occurs due to chaotropic interactions with quaternary ammonium groups, shlelded by external weak carboxylic acld groups, which themselves interact with eluent catlons according to increasing charge. These effects were exploited to demonstrate a previously unreported cation charge gradlent approach to anlon separations, resulting in considerable reductions in retention times whilst maintaining resolution. In addition, the new phases were used wlth a novel combined triple eluent concentration, pH and flow gradient technique for the simultaneous separation of 18 nucleotides, nucleosides and nucleobases and the method developed as applied to the separation of nucleic acids precursors in yeastolate samples. An nvestigation into the retention of transltlon metal cations was also made and it was hown that cations could be simultaneously separated with inorganic anions, as anlonlc complexes with the eluent anion, on the new zwitterionlc phase. This simultaneous separation of inorganic anions and cations was shown and optimised conditions were applied to the separation of anions and cations in a natural water sample. Finally, the application of short monolithic zwittenonlc columns for anion separations was investigated, w~ t hth e separation of 6 anions obtalned under flow gradlent conditions on a 4 mm - long column coated with N-(dodccyl-N,N-dimethylarnmonio)undecanoate and an application to the analysis of a sallne sample is shown.
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