Capillary modification by noncovalent polycation adsorption: Effects of polymer molecular weight and adsorption ionic strength

The strong polycation poly(dimethyldiallylammonium chloride) (PDADMAC) was noncovalently immobilized on fused-silica capillaries. The stability and ef ficiency of the adsorbed coating was studied as a function of polymer molec ular weight and coating ionic strength. By monitoring the electroosmotic fl ow on PDADMAC-coated capillaries, we found that optimal surface coverage is achieved using high molecular weight polycations at high ionic strength. S uch capillaries can be used to elute positively charged proteins. In this s tudy, true protein mobilities were obtained by (1) extrapolation of effecti ve mobility to desired conditions and (2) theoretical calculation from the Henry function. By comparing apparent protein mobility with true protein mo bility, we demonstrated that the protein-polycationic capillary surface int eraction could enhance the selectivity of the silica capillary for separati on of BSA and beta-lactoglobulin.