A cationic β-cyclodextrin as a dynamic coating for the separation of proteins in capillary electrophoresis

A cationic cyclodextrin was used as dynamic coating for the capillary electrophoresis of a model mixture of proteins (i.e., ubiquitin, α-lactoglobulin, cytochrome-c, and myoglobin) as positively charged species in a fused silica capillary. An interesting feature of the coating is that by simple adjustment of the concentration of cyclodextrin added into the background electrolyte, a neutral or positively charged surface, which was beneficial in preventing protein adsorption at the inner capillary wall surface, was obtained. This is the first demonstration of a dynamic coating that yielded a neutral surface for protein separations in capillary electrophoresis. Based on electro-osmotic flow measurements, addition of 0.05 to 0.10 mg/mL quaternary β-cyclodextrin in a low pH electrolyte resulted in a neutral or positive surface (undetectable to very slow anodic electro-osmotic flow). The coating approach afforded the electrophoretic separation of the mixture of proteins at positive polarity with good repeatability and separation performance.