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 efficiency of the adsorbed coating was studied as a function of polymer molecular weight and coating ionic strength. By monitoring the electroosmotic flow on PDADMAC-coated capillaries, we found that optimal surface coverage is achieved using high molecular weight polycations at high ionic strength. Such capillaries can be used to elute positively charged proteins. In this study, true protein mobilities were obtained by (1) extrapolation of effective mobility to desired conditions and (2) theoretical calculation from the Henry function. By comparing apparent protein mobility with true protein mobility, we demonstrated that the protein-polycationic capillary surface interaction could enhance the selectivity of the silica capillary for separation of BSA and beta-lactoglobulin.