Capillary Electrophoresis–Mass Spectrometry for Metabolomics Using New Interfacing Designs
In metabolomics, capillary electrophoresis–mass spectrometry (CE-MS) using electrospray ionization (ESI) has become a useful analytical technique for the profiling of highly polar and charged metabolites. In general, a co-axial sheath-liquid interface is employed for coupling CE to MS. In this approach, the ESI process is mainly dictated by the sheath-liquid and not the CE effluent. A wide range of sheath-liquid compositions with or without additives can be explored in order to improve the ESI process, and as such, this interfacing approach provides a high degree of flexibility. Though CE-MS using a sheath-liquid interface can be used in a rather robust way for metabolic profiling studies, the significant dilution of the CE effluent (10–100 nL min−1) by the sheath-liquid, which is generally provided at a flow-rate between 2 and 10 µL min−1, can be considered as a major drawback for global metabolic profiling. Recent advances in interfacing designs allow CE-MS to be used under low flow-rate conditions. In this context, the sheathless porous tip interface, the flow-through microvial interface and the electrokinetic-driven sheath-liquid interface have emerged as important recent developments. In this chapter, the utility of CE-MS using these new interfacing designs is demonstrated by representative examples in the fields of biomedical and clinical metabolomics.