Capillary electrophoresis–electrospray ionization-mass spectrometry using fused-silica capillaries to profile anionic metabolites

A capillary electrophoresis–electrospray ionization-mass spectrometry (CE–ESI-MS) method is proposed to profile anionic metabolites. This application is based on the use of a bare fused-silica capillary in two different characteristic modes, high-speed and high-resolution. The high-speed mode aims to simultaneously analyze a number of major anionic metabolites including organic acids, sugar phosphates, nucleotides and coenzymes. Using ammonium formate (pH 8.0) as the electrolyte and applying pressure-assisted flow, a standard mixture including 38 compounds can be analyzed in this way in less than 16 min. The relative standard deviations were better than 0.7 for the migration times and between 1.2 and 7.0 for the peak areas. However, the peaks of several isomers overlapped. Thus, a high-resolution mode was developed for these isomers. In this mode, a mixture of ammonium acetate (pH 10.0) and methanol as electrolyte allowed such isomers to be separately analyzed. The relative standard deviations were better than 0.9 for migration times and between 1.5 and 6.3 for peak areas. This was particularly advantageous for hexose phosphate isomers, which are difficult to separate using existing CE–MS methods. To evaluate the effectiveness of our proposed method, we performed metabolite profiling of extracts from moss. In the high-speed mode, all target metabolites except isocitrate could be determined. In the high-resolution mode, five successive peaks were obtained corresponding to the hexose phosphate isomers mannose 6-phosphate, glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate and an unknown compound. These results indicate that our new method has great utility in the profiling of anionic metabolites.