Micropreparation of peptides by capillary electrophoresis for matrix assisted laser desorption mass spectrometry

In the separation of peptides by capillary electrophoresis and analysis by matrix assisted laser desorption mass spectrometry, strong suppression of the mass spectrometric signals is a problem with many common electrolytes used in the separation step such as sodium phosphate. We describe an approach employing individual electrolytes selected for highest performance in each process. Suppression with samples collected into phosphate buffers is avoided when citrate, trifluoroacetic acid or hydrochloric acid is used for collection, while phosphate still provides excellent resolution in the capillary. Low concentrations of hydrochloric acid added to the sample/matrix mixture generate essentially adduct-free mass spectra with better signal-to-noise ratios and detection limits (fmol range) than those obtained with citrate or trifluoroacetic acid. Addition of 0.25% ethylene glycol to both the phosphate electrolyte and the sample improves peak shape and resolution, and is crucial for preparative separations in large diameter capillaries.