A Low-Makeup Beveled Tip Capillary Electrophoresis /Electrospray Ionization Mass Spectrometry Interface for Micellar Electrokinetic Chromatography and Nonvolatile Buffer Capillary Electrophoresis

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Abstract
A robust interface has been developed for interfacing micellar electrokinetic chromatography (MEKC) and nonvolatile buffer capillary electrophoresis (CE) to electrospray ionization mass spectrometry (ESI-MS). The interface consists of two parallel capillaries for separation (50 μm i.d. × 155 μm o.d.) and makeup (50 μm i.d. × 155 μm o.d.) housed within a larger capillary (530 μm i.d. × 690 μm o.d.). The capillaries terminate in a single tapered tip having a beveled edge. The use of a tapered beveled edge results in a greater tip orifice diameter (75 μm) than in a previous design from our laboratory (25 μm) that used a flat tip. While maintaining a similar optimum flow rate and consequently similar sample dilution, a 75-μm beveled emitter is more rugged than a 25-μm flat tip. Furthermore, the incorporation of a sheath liquid capillary allows the compositions of the final spray solution to be controlled. The application of this novel CE/ESI-MS interface was demonstrated for MEKC using mixtures of triazines (positive ion mode) and phenols (negative ion mode). The ability to perform CE/ESI-MS using a nonvolatile buffer was demonstrated by the analysis of gangliosides with a buffer consisting of 40 mM borate and 20 mM α-cyclodextrin.