Simultaneous iso-electric focusing of proteins in a micro-fabricated capillary coated with hydrophobic and hydrophilic plasma polymerized films

The ability to modify and reduce the electroosmotic flow (EOF) is one of the most influential parameters which affects iso-electric focusing (IEF) of proteins. Therefore capillaries are usually coated with polymers or gels to prevent non-specific adsorption and suppress the EOF in capillary iso-electric focusing (cIEF) of proteins. In this research hexamethyldisiloxane (HMDS) and 2,3-epoxy-1-propanol (glycidol) plasma polymerized films were deposited onto both surfaces of the capillary separation channel. Cathode solution pH 3, anode solution pH 10 and a carrier ampholyte, pharmalyte provided the necessary stable pH gradient. Simultaneous IEF of proteins in capillaries coated with hydrophobic and hydrophilic plasma polymerized films occurred within minutes. The electroosmotic force of uncoated glass capillaries was suppressed by 50% after deposition of 200 nm 2,3-epoxy-1-propanol compared with a 30% reduction of EOF when the capillary was coated with 200 nm HMDS. The hydrophilic 2,3-epoxy-1-propanol plasma polymerized film was more resistant with a stronger attachment to the glass surface than previously prepared acetonitrile plasma polymerized films.