Database of free solution mobilities for 276 metabolites

Although databases are available that provide mass spectra and chromatographic retention information for small-molecule metabolites, no publicly available database provides electrophoretic mobility for common metabolites. As a result, most compounds found in electrophoretic-based metabolic studies are unidentified and simply annotated as "features". To begin to address this issue, we analyzed 460 metabolites from a commercial library using capillary zone electrophoresis coupled with electrospray mass spectrometry. To speed analysis, a sequential injection method was used wherein six compounds were analyzed per run. An uncoated fused silica capillary was used for the analysis at 20 °C with a 0.5% (v/v) formic acid and 5% (v/v) methanol background electrolyte. A Prince autosampler was used for sample injection and the capillary was coupled to an ion trap mass spectrometer using an electrokinetically-pumped nanospray interface. We generated mobility values for 276 metabolites from the library (60% success rate) with an average standard deviation of 0.01 × 10^-8 m²V^-1s^-1. As expected, cationic and anionic compounds were well resolved from neutral compounds. Neutral compounds co-migrated with electro-osmotic flow. Most of the compounds that were not detected were neutral and presumably suffered from adsorption to the capillary wall or poor ionization efficiency.