Interfaces for Coupling Capillary Electrophoresis with Mass Spectrometry

Interfaces for Coupling Capillary Electrophoresis with Mass Spectrometry 

Almost all operational modes of capillary electrophoresis have been combined with mass spectrometry via CF-FAB [68-70], MALDI [57,71], and ESI [72-76]. Of these three technologies, ESI has attained an enviable status as the interface of choice to couple CE with mass spectrometry. A CE/MS interface must address the problem of the low liquid flow rates of the CE process. Other considerations are buffer compositions and electrical contact between the separation buffer and the interface. As with LC/MS systems, only volatile buffers are tolerated in a CE/MS operation. Also, high salt concentrations must be avoided for stable operation of a mass spectrometry system. 

The coupling CE through the sheathless concept is optimally achieved via a nano-ESI source because both operate at uL/min flow rates. In one version, the CE column is connected to the sprayer tip via a microdialysis device [77,78]. In another simple version, a single piece of tapered CE column with a 20-p,m-i.d. tip has been used for separation as well as microspraying [78]. This combination results in high ionization efficiency and low detection limit. The detection limit of 0.1 to 5 finol for peptide standards has been reported. 

The sheathless design has the advantages of high detection sensitivity, low flow rates, long-term stability, and the absence of interference from the sheath liquids. A major concern of this design is to find an optimum buffer combination for CE separation and ESI operation. 

Some more interfaces are available that combine the versatiUty of the sheath-liquid design with the sensitivity of the sheathless format. In one design, two 

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