Capillary Electrophoresis-Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for the Identification of Cationic Metabolites via a pH-Mediated Stacking-Transient Isotachophoretic Method

Capillary electrophoresis−mass spectrometry (CE−MS) is still widely regarded as an emerging tool in the field of metabolomics and metabolite profiling. A major reason for this is a reported lack of sensitivity of CE−MS when compared to gas chromatography−mass spectrometry GC/MS and liquid chromatography−mass spectrometry. The problems caused by the lack of sensitivity are exacerbated when CE is coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), due to the relatively low data acquisition rate of FT-ICR MS. Here, we demonstrate the use of an online CE sample preconcentration method that uses a combination of pH-mediated stacking and transient isotachophoresis, coupled with FT-ICR MS to improve the overall detection of cationic metabolites in the bacterium Desulfovibrio vulgaris Hildenborough. This method showed a significant increase in signal-to-noise ratio when compared to CE normal sample stacking, while providing good separation efficiency, reproducibility, and linearity. Detection limits for selected amino acids were between 0.1 and 2 μM. Furthermore, FT-ICR MS detection consistently demonstrated good mass resolution and sub-ppm mass accuracy.