Influence of capacity on the retention characteristics in Zwitter Ion Chromatography (ZIC) and ZICHydrophilic Interaction Chromatography (HILIC) onfour different sulfobetaine stationary phases

A number of covalently bonded zwitterionic stationary phases with inner quaternary amines and outer sulfonic acids in varying capacities was synthesized based on poly (styrene-DVB) particles by graft polymerization. The different spacer lengths and capacities are used as an investigative tool, fo...

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Bibliographic Details
Main Author: Rasheed, Ashraf Saad
Contributors: Seubert, Andreas (Prof. Dr.) (Thesis advisor)
Format: Dissertation
Language:English
Published: Philipps-Universität Marburg 2014
Chemie
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Summary:A number of covalently bonded zwitterionic stationary phases with inner quaternary amines and outer sulfonic acids in varying capacities was synthesized based on poly (styrene-DVB) particles by graft polymerization. The different spacer lengths and capacities are used as an investigative tool, for the retention behavior of the inorganic anions in ZIC and ZIC-HILIC modes. The separation mechanism is explored by varying eluent ionic strength, eluent pH and the volume fraction of organic modifier. Remarkably, the increasing capacity exhibits different characteristics of anions retention for all exchangers in two modes. Hence, this leads to increased, decreased or no significant change in the retention times of inorganic anions. Moreover, no change in the separation mechanism and selectivity of anions occurred when investigating the influence of eluent concentration, pH of eluent and acetonitrile content for various capacities of zwitterionic columns. It should be noted that high values of the capacity of the SB2-exchanger exhibit a different separation mechanism for inorganic anions in comparison to a previous study made for the ZIC-mode. Furthermore, a new correlation between spacer length and the capacity and their impact on the retention time of anions in ZIC and ZIC-HILIC modes were found. The results of variations of acetonitrile content, buffer concentration and mobile phase pH show that pharmaceuticals can be separated based on hydrophilic, hydrophobic and anion/cation-exchange interactions between the stationary phase and analyte. For a differentiation between the separation mechanism for the first time a set of cation and anion exchangers based on the same core material has been used as investigative tool. In addition, we have proven the suitability of ZIC-HILIC stationary phases for the determination of the chromatographic hydrophobicity parameter. The pharmaceutical deferoxamine mesylate (DFOM) is a chelating agent which forms complexes with multiple charged metal ions of biological importance (Fe3+, Al3+) and other metals. We could demonstrate that the sulfobetaine exchangers are able to separate the Fe(III)- DFOM and Al(III)-DFOM complexes by IC-ICP-AES. The results of the eluent ionic strength and pH variations show that metal-DFOM complexes were separated based on a cation exchange mechanism. Excess adsorption isotherms of water from acetonitrile were measured for ten zwitterionic stationary phases (eight sulfobetaine exchangers have been prepared and two commercially available stationary phases) using the minor disturbance method. The retention factors of the eight pharmaceutical compounds (Deferoxamine mesylate, Thiamine.HCl, Diclofenac sodium, Cyclopentolate.HCl, Dexamethasone sodium phosphate, Tetracaine.HCl, Pilocarpine .HCl and Chloramphenicol) can be correlated with the maximum excess of water adsorption.
DOI:https://doi.org/10.17192/z2014.0498