Development of novel polymer monoliths for fast ion chromatography

This thesis focuses on the development of latex agglomerated ion-exchange materials for applications in capillary ion chromatography (IC). The continuous rod, monolithic polymer columns were predominantly synthesised in-situ in micro-format – within capillaries of 1 mm internal diameter and below - useable in traditional as well as current high-end capillary IC instruments. Recent developments in monolithic stationary phases for the fast analysis of inorganic ions and other small molecules in IC and capillary electrochromatography (CEC) concentrate in particular on the properties of organic (polymer) monolithic materials and inorganic (silica-based) monoliths and specific applications. The project path has encompassed fabrication, characterisation and chromatographic investigation of monolayer AS18 latex-coated, sulfonated poly(chloromethylstyrene-co-divinylbenzene) (poly(CMS-co-DVB)) monoliths and their commercial counterpart – the Dionex Ionswift\(^{TM}\) Max Series. Subsequent to the synthesis work, the non-destructive morphology and capacity assessment by capacitively-coupled contactless conductivity detection (C\(^4\)D) and the comprehensive study of this technique in relation to methacrylate based, strong anion-exchanger (SAX) polymer monoliths in capillary format revealed the potential and shortfalls of the detection technique to predict monolithic column performance. Monolayer latex-coated, functionalised poly(CMS-co-DVB) monolithic porous polymer scaffolds were measured with capacities of 34 μequiv/g and plate heights of 26,000 plates/m. The direct surface functionalised (non-coated) SAX version exhibited values in both capacity and plate number more than double in magnitude, which is ascribed to the actual surface and pore morphology of the polymer materials with different levels of hydrophobicity. C\(^4\)D was used to non-invasively evaluate the internal make-up of the capillary columns, consisting of a combination of morphology and surface chemistry. Measurements were made by scanning the conductance of the mobile phase filling the pores of the substrate, with and without the surface functional conductivity of the scaffold, over the length of the capillary section using an automated, motorized stage. The findings were well matched with scanning electron microscopy (SEM) images of the capillary cross-sections at discrete locations and further confirmed with chromatographic testing, such that higher conducting, smooth profile yielding columns were predictably exhibiting better separation performance over versions that yielded more irregular conductivity profiles. The extension of this work on latex-coated, functionalised poly(CMS-co-DVB) monoliths in capillary format to coatings with differently sized AS11 latex particles showed that the extent and type of coating are of lower influence on the chromatographic performance in comparison to well defined, uniformly porous morphology of the polymer substrate. Other material surface effects, such as gel porosity and the level of hydrophobicity in relation to the eluents and solvents used, appear to have significant effects on both the synthesis process and the final column chromatographic performance