A low-makeup beveled tip capillary electrophoresis/electrospray ionization mass spectrometry interface for micellar electrokinetic chromatography and nonvolatile buffer capillary electrophoresis

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 mum i.d. x 155 mum o.d.) and makeup (50 mum i.d. x 155 mum o.d.) housed within a larger capillary (530 pm i.d. x 690 mum 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 mum) than in a previous design from our laboratory (25 mum) that used a flat tip. While maintaining a similar optimum flow rate and consequently similar sample dilution, a 75-mum beveled emitter is more rugged than a 25-mum 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 alpha-cyclodextrin.