Analysis of protein fractions by micropreparative capillary isoelectric focusing and matrix-assisted laser desorption time-of-flight mass spectrometry.

In this study, the use of capillary isoelectric focusing (cIEF) as a micropreparative tool for protein analysis by matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS) is demonstrated. A newly designed, automated, collection interface equipped with a fiber-optic UV detector and a sheath flow connection was employed for collection of protein fractions. Multiple fractions were collected during a single cIEF run and further analyzed by MALDI-TOF-MS for mass assignment. The feasibility of the method was tested with a mixture of model proteins with different isoelectric points and molecular masses, and with variants of human hemoglobins differing in pI, but with negligible difference in M(r). Some practical considerations of the collection procedure and subsequent TOF analysis are presented.