Capillary electroseparations of some di-, tri-, and tetrapeptides and enkephalin-related peptides

Electrophoretic mobilities and capacity factors for short peptides were determined in micellar electrokinetic systems (MEKC) using UV detection at 210 nm. On the basis of determined capacity ratios, taurodeoxycholic acid was found to be a selective micellar agent for peptides. Structural features other than hydrophobicity were found to be decisive for the distribution of the peptides to the micellar phase. Basic peptides of enkephalin-type containing arginine were more highly distributed to the micelles than others, indicating the importance of electrostatic forces in the distribution mechanism. In systems with polyacrylamide-coated capillaries, the micellar velocity toward the anode is larger than the electroosmosis, and conditions permitting splitting of a series of related peptides, i.e., some peptides migrating with the micelles and others toward the cathode resulting in infinite selectivities, were developed. Separation by micellar electrokinetic chromatography is demonstrated to be a suitable alternative for peptides that are difficult to separate by capillary zone electrophoresis.