Field-enhanced sample injection for high-sensitivity analysis of peptides and proteins in capillary electrophoresis–mass spectrometry

Field-enhanced sample injection (FESI) was used to improve the concentration sensitivity of a capillary electrophoresis (CE)–mass spectrometry (MS) system with sheath flow configuration. Using some bioactive peptides, more than 3000-fold improvement in signal was obtained, permitting analysis in the low nM (fmol/μl) levels. The system was further evaluated for analysis of complex peptide mixtures by using low concentration tryptic digests of standard proteins. Rapid identification of the original protein was obtained by database searching using the observed molecular masses of the peptides, and by comparison of actual MS–MS spectra of selected peptides with the predicted fragmentation patterns.