Sheathless capillary electrophoresis-electrospray ionization mass spectrometry using 10 mu m I.D. capillaries: analyses of tryptic digests of cytochrome c.

The analyses of tryptic digest of proteins present a difficult challenge to the analytical chemist due to the wide range of molecular masses and hydrophobicities of the peptides produced. In this study, we demonstrate the separation of tryptic digests of bovine, Candida krusei and equine cytochrome c using a new electrospray ionization (ESI) interface for CE-MS that does not require additional sheath make-up fluid or mechanical assistance to aid the ESI process. The utility of this new CE-ESI-MS interface is demonstrated using a 10 microm I.D. CE capillary where the injected sample amounts are in the 30 femtomole (of protein) region. The CE electroosmotic flow rates when aminopropylamine treated capillaries are utilized are in the 10 nl/min region for a relatively conductive buffer system (0.01 M ammonium acetate-acetic acid buffer system, pH 4.4 and a 300 V/cm field strength).