Sheath-flow capillary electrophoresis-mass spectrometry (CE-MS) has emerged as a new tool for comprehensive analysis of charged metabolites. However, it needs to be more sensitive. Here, we report a sheathless capillary electrophoresis-electrospray ionization-mass spectrometry method for cationic metabolome analysis. This system used a high-sensitivity porous sprayer interface and 10% (v/v) acetic acid as the background electrolyte (BGE). Under optimized conditions, 53 cationic metabolites, including amino acids and their derivatives, amines, nucleic acids and small peptides, were successfully separated and selectively detected with a time-of-flight mass spectrometer. At a signal-to-noise ratio of three, the concentration detection limits for these compounds were between 0.004 and 0.8 μmol L-1 (amount detection limit, 0.01 to 2 fmol) with pressure injection at 20.7 kPa for 5 s (2.6 nL). Compared with conventional sheath-flow CE-MS, the detection limit of the present method was increased more than 5-fold for 21 (40%) of the compounds detected. When the method was applied to the analysis of cationic metabolites obtained from human urine, there was a 10-fold increase in the number of detected peaks compared with conventional methods. More than 180 successive runs could be conducted without any problems, and only the BGE needed to be changed.
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