The fabrication and modification of capillary polymer monoliths for the separation of small ions

Abstract

The fabrication and modification of polymer monoliths, in capillary formats, for the separation of small ions is presented. The separation of small ions using polymer monoliths has limitations and this work aims to investigate increasing the ion exchange capacity using photo-grafting techniques. Chapter 1.0 includes a comprehensive review on the use of capillary ion chromatography including advancements made in capillary instrumentation, stationary phases and detection devices. This chapter also includes the various methods of modifying stationary phase with ionogenic functionalities suitable for use in capillary ion chromatography. Chapter 2.0 shows the modification of polymer monoliths with quaternary ammonium ions, namely poly([2(methacryloyloxy)ethyl] trimethylammonium chloride) with immobilisation of the ion exchange functionalities taking place using photo-grafting techniques. In this work, the method of functionalisation of the polymer monolith was compared to a previously published polymer monolith bearing the same ion exchange functionalities. Chapter 2.0 also includes the separation of anions using a portable inhouse assembled capillary ion chromatography system. In Chapter 3.0, the photo-grafting of poly(3-sulfopropyl methacrylate) on a polymer monolith for the separation of cations is presented. The effect of temperature on the retention of Mg(II), Ca(II) and Ba(II) was carried out using an in-house constructed capillary column heater which was easily incorporated into the ion chromatography system. This chapter also introduces post-column reaction chemistry which involves the reaction of the eluted metals with a suitable reagent in a post-column mixer and detection of the coloured complex formed. In this work, the use of polymer monoliths as post-column mixers was investigated. Monoliths prepared with increasing pore size were incorporated into a flow injection analysis system and their suitability as postcolumn mixers was determined and compared to a commercially available postcolumn mixer. Chapters 4.0 and 5.0 deal with the immobilisation of chelating ligands on a polymer monolith to produce a capillary chelating ion exchanger. Two methods of immobilisation of the chelating ligand were identified and compared. Scanning capacitively coupled contactless conductivity detection was used to characterise the chelating stationary phases. Chapter 5.0 includes the use of a novel bimodal detector set-up i.e. on-column C4D was used in conjugation with UV-Vis detection following the reaction of the eluted metals with a post-column reagent. Chapter 4.0 shows applications of the capillary chelating ion exchangers including the determination of Ca(II) and Mg(II) in bottled water samples and also the separation of metal cations in a spiked sea-water samples