Development of a Robust Capillary Electrophoresis–Mass Spectrometer Interface with a Floating Sheath Liquid Feed

The on-line combination of capillary electrophoresis (CE) with electrospray ionisation mass spectrometry (ESI-MS) has attracted major attention for the in-depth analysis of complex samples. However, CE-MS coupling is not straightforward. We present a novel coaxial sheath liquid CE-MS interface, which is robust and can be used for both hyphenated techniques, liquid chromatography-mass spectrometry (LC-MS) and CE-MS, alternatively on the same mass spectrometer. The two separation techniques can be switched within minutes. To obtain a stable ion spray and avoid electrical problems, the CE-power supply is used to produce the potential for the CE separation and the ESI sprayer tip simultaneously. The necessary sheath liquid is delivered by a pump which floats on the ion sprayer potential of the mass spectrometer, avoiding any current flow towards ground. The sole parameter which has to be adjusted to adapt to different CE conditions is a variable resistor. Analytical applications such as peptide mixture analysis and drug screening are presented