Latex-coated stationary phases for preconcentration and separation in capillary electrochromatography

This work presents a systematic study on the use of latex-coated stationary phases for on-column ion-exchange preconcentration of anions by capillary electrochromatography with elution by a transient isotachophoretic gradient. Fully functionalised quaternary ammonium latex particles were electrostatically bound to open tubular (OT) capillaries and porous monolithic capillary columns. These columns were characterised and provided a reproducible and simple means for creating ion-exchange stationary phases with reversed electroosmotic flow. Monolithic columns provide a chromatographic support of high surface area, high phase ratio and are highly permeable. Adsorption of latex-particles provides superior mass-transfer properties ideal for ion-exchange preconcentration and ion-exchange capillary electrochromatography (IE-CEC). The prepared columns were characterised by their retention in IE-CEC when the ion-exchange interaction was varied through manipulating the strength and nature of the competing ion. Porosimetry and scanning electron microscopy were used to characterise the monolithic surface and architecture. Up to 300,000 plates/column were achieved using latex-coated silica monolithic columns and 164,000 plates/column were achieved on methacrylate analogues. Both silica and methacrylate latex-coated monolithic columns were of similar capacity and around 20 times greater when compared to OT counterparts. A monolayer coverage of latex particles was not evident on the monolithic columns created and resulted in mixed mode interaction for the separation of organic anions on a polymer support. Multi-mode columns were created using zero-dead volume unions to attach a second capillary segment for the purpose of separation and detection and allowed individual optimisation of the discrete segments. Decoupling of the preconcentration column allowed in situ preconcentration of a river water sample, which was brought back to the laboratory for analysis. Novel discontinuous electrolyte combinations were used to increase the range of analytes which could be preconcentrated and detected. Alkylsulfonates were found to be ideal strong electrolytes of low electrophoretic mobility and were able to efficiently elute a large range of inorganic and organic anions. Further efforts to increase the range of anions which can be preconcentrated and detected included the use of a miniaturised capacitively coupled contactless conductivity detector and indirect UV detection. High capacity monolithic columns were suitable for sample-cleanup procedures and were applied to the preconcentration of iodide in Southern Ocean seawater. Detection limits of 11 pM were achieved for iodide when selective focusing occurred at the isotachophoretic boundary using IE-CEC.