Multidimensional separation approaches for complex sample analysis : two-dimensional ion chromatography ‚Äöv¿vØ capillary electrophoresis

The work presented in this thesis describes development, evaluation and implementation of an online interfacing/modulation technique for comprehensive two-dimensional ion chromatography ‚Äöv¿vØ capillary electrophoresis (IC ‚Äöv¿vØ CE) separation of low-molecular-mass ionic or ionogenic compounds. Chapter 1 provides an insight into the evolution of multidimensional liquid-phase separations combining both chromatography and electrophoresis from inception in 1948 to present. As noted in this chapter, column-based multidimensional electrophoretic and chromatographic separations have shown to be powerful complementary techniques to the traditional two-dimensional gel-electrophoresis approaches; especially for the analysis of lower molecular-mass-molecules in addition to proteins and peptides. However, complexities in instrumentation and online interfacing technologies are known to have hindered development of such techniques. Chapter 2 introduces a non-focusing interfacing technology for online hyphenation of ion chromatography with capillary electrophoresis. The system compromised of an in-house sequential-injection capillary instrument which, through the use of a two-position six-port injection valve, allowed comprehensive sampling of the IC effluent for quantitative analysis of inorganic anions and haloacetic acids in water. In addition to instrumental developments, the second section of this thesis focuses on alternative method development approaches for screening/optimisation of IC ‚Äöv¿vØ CE separations. Chapter 3 demonstrates the impact of background electrolyte pH on sample dimensionality and peak capacity for IC ‚Äöv¿vØ CE separation of multi-valent lowmolecular-mass organic acids. In this chapter, a simplified screening approach based on calculation and maximising of Euclidean distance between the two-dimensional peaks was used to predict the optimal background electrolyte pH in CE as well as the eluent profile in IC. However, due to lack of overall two-dimensional selectivity, further investigations were necessary to make full resolution of the analytes possible. In Chapter 4, based on a ground set by the findings presented in Chapter 3, a universal framework is proposed for simultaneous screening of separation selectivity in both dimensions as a preceding step in method development/optimisation of twodimensional separations. In this chapter, through the introduction of the concept of two-dimensional selectivity mapping, effect of stationary phase in IC and background electrolyte pH in CE on the overall two-dimensional separation selectivity was studied to enable full resolution of the organic acids. Finally, Chapter 5 of this thesis discusses the limitations of IC ‚Äöv¿vØ CE and provides further insight and direction for future research.