A Low-Flow CE/Electrospray Ionization MS Interface for Capillary Zone Electrophoresis, Large-Volume Sample Stacking, and Micellar Electrokinetic Chromatography

Abstract

A simple and versatile low-flow interface has been developed for interfacing capillary electrophoresis (CE) with electrospray ionization (ESI) mass spectrometry. This low-flow interface showed better sensitivity than a conventional sheath liquid interface, primarily attributed to a low dilution factor and a reduction in the sprayer orifice size. The interface was also found to be more tolerant to the presence of nonvolatile salts. Because of tolerance to the surfactant SDS, this interface can be used to couple micellar electrokinetic chromatography (MEKC) with ESI-MS. The performance of the interface in an MEKC-MS application, as demonstrated in the analysis of triazines, was significantly better than that obtained with a conventional sheath liquid interface. Moreover, this interface can be easily used for large-volume sample-stacking (LVSS) applications. Using a series of phenols as a test case, an approximate 500-fold enrichment was achieved by LVSS in conjunction with the low-flow CE/MS interface described.

MEKC: An update focusing on practical aspects

“…One of the major drawbacks, however, is that the high flow rate of the sheath liquid dilutes the analyte band and decreases the sensitivity. Her and co-workers [184,185] have developed two interesting approaches to increasing the sensitivity of the sheath liquid interface. Their original design consisted of a low-flow interface with a nanospray flat tip [184] that increased the sensitivity by effect of its high salt tolerance, and superior ionization and sample efficiency.…”

Quantitation in capillary electrophoresis-mass spectrometry

“…However, if the ultimate in sensitivity is required the sheathless design is preferred due to its higher ionization efficiency in this nanospray design [15]. Attempts have been made to optimize all interfaces: By reducing the sheath liquid flow the ionization efficiency has been tried to increase [16][17][18], however, "nonstandard" capillaries (OD 180 mm) are required. On the other hand the lifespan of the capillary can be increased by using capillary tip coatings based on conductive polymers [19].…”

Coupling CE with atmospheric pressure photoionization MS for pharmaceutical basic compounds: Optimization of operating parameters

“…This interface is the critical part in the connection of both instruments and the main reason that CE-ESI/MS is not considered a routine technique. Currently, the commercial sheath liquid configuration, where an additional liquid is mixed to the CE effluent, is the most rugged and easy tool to implement CE-ESI/MS [5][6][7][8][9][10]. Sheath liquid provides (i) electrical contact with the outlet end of the separation capillary, (ii) appropriate flow rate adapted to source configuration, and (iii) suitable solvent conditions for ionization and evaporation, independent on the nature of the BGE.…”