ABSTRACT
B. Modified Polymer Capillaries Chemical treatments to form a hydrophilic layer on the inner wall of PP fibers were described. Compared to the procedures used for coating fused-silica capillaries, it is easier to achieve the in situ polymerization of a monomer inside the PP tubings: The monomer is directly copolymerized with the polymer of the capillary wall, in the presence of a free-radical initiator. Moreover, the problems of coatings stabilities are addressed, as the polymeric layer is attached to the capillary wall via C-C linkages. This approach was used by Lee's group [78, 79] to graft polyacrylamide coatings onto PP and PBT hollow fibers. Because of the large UV absorption with the PBT fibers, a connection with a piece of fused-silica tubing was needed for the on-line UV detection. Model proteins were separated with high efficiencies (3. 7 x 105 plates/m) using a polyacrylamide-modified PP hol-
With PP surfaces modified by reacting and cross-linking of allyldextrane [80], the same approach was not successful in eliminating protein adsorption, as the CZE peaks of proteins were broad and asymmetric. Instead, the physical adsorption of phenyldextran gives uniformly coated hydrophilic layers on the PP surface and protein separations with sharp peaks were achieved, even after washing with a O.lM NaOH solution.
