UBC Theses and Dissertations
Design and applications of an improved capillary electrophoresis - electrospray ionization - mass spectrometry interface Zhong, Xuefei
A novel capillary electrophoresis – electrospray ionization – mass spectrometry (CE-ESI-MS) interface has been developed to provide a robust, user-friendly and more sensitive alternative interface strategy. The new interface uses a flow-through microvial design and a bevelled sprayer tip geometry. The capillary column terminus is surrounded by a tapered stainless steel hollow needle, and the interior of the needle tip acts as the CE outlet while its exterior tip surface provides the electrode surface for electrospray ionization. A chemical modifier is supplied to the open-ended microvial at the CE outlet through a standard tee union, serving the purpose of maintaining electrical continuity, and supporting a stable electrospray. The chemical modifier supplied through the flow-through microvial can also be used to improve the compatibility of CE effluent with electrospray ionization. The bevelled sprayer tip design extends the optimal flow rate range for ESI and requires lower flow rate compared to conventional blunt tips or symmetrically tapered sprayer tips. This feature leads to reduced dilution effect caused by the chemical modifier solution and improves the detection sensitivity. The mass transport process in the flow-through microvial was investigated by numerical simulation and experimental comparison of on-column and post-column detection. Both approaches demonstrated that the laminar flow profile inside the microvial does not significantly distort the peak shape and the major characteristics of the eluted peaks are maintained when the modifier flow rate is properly adjusted. The chemical modifier solution in the flow-through microvial enables CE separation without electroosmotic flow (EOF). One useful application of this feature is interfacing online capillary isoelectric focusing (cIEF) with ESI-MS detection, which could be a potential replacement in many applications of two-dimensional gel electrophoresis (2DE) for protein analysis in the future. The final part of the thesis elucidates the electric field distribution in the ESI source with an atmospheric ion lens, which could be incorporated in the CE-ESI-MS interface to improve the ionization and sampling efficiency in the future.
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