Capillary Isoelectric Focusing Separation Combined with Mass Spectrometry Using Sonic Spray Ionization for Protein Analysis.

Capillary isoelectric focusing (CIEF) separation combined with mass spectrometry for protein analysis has been demonstrated by using a sonic spray ionization (SSI) interface, which has a buffer reservoir between the ion source and the separation capillary. Since the buffer reservoir was used as an outlet reservoir for CIEF, on-line and one-step CIEF/MS was possible. In SSI, since a sample solution is sprayed at any solution-flow rate from a sample-introduction capillary with a high-speed gas flow, high-polymer ampholytes for CIEF can be used without clogging up the spray nozzle of the interface. Also, additives such as ampholytes significantly decrease ion intensity of analyte molecules; however, the SSI interface whose reservoir is filled with an acetic acid solution minimizes the decrease in ion intensity of the analyte. We combined CIEF with an ion trap mass spectrometer and were able to detect 160 fmol of myoglobin and cytochrome-c.