LIQUID SHEATH EFFECTS ON THE SEPARATION OF PROTEINS IN CAPILLARY ELECTROPHORESIS ELECTROSPRAY MASS-SPECTROMETRY

Ionic migration in capillary electrophoresis/electrospray mass spectro metry using a coaxial sheath liquid interface was investigated. Format ion of moving ionic boundaries inside the capillary was observed due t o migration of liquid sheath counterions into the separation capillary . Either sharp or diffuse ionic boundaries were created, leading to de lays or inversions in migration order and, at times, loss of resolutio n. The conditions of formation and minimization of ionic boundaries ha ve been studied both theoretically and experimentally. It has further been demonstrated that diffucult-to-spray electrolytes (such as phosph ate-containing buffers) can be used for capillary electrophoresis/mass spectrometry when liquid sheath counterions replace the background el ectrolyte counterions.