ABSTRACT
Grafting with an Intermediate Polymeric Layer An original strategy was introduced by Karger's group [74] to attach two polymeric layers to the surface. In this method, the prior treatment of the capillary surface with NaOH and/or HCl is omitted. A cross-linked poly(methylvinylsiloxane) layer is formed by statically coating the inner wall of the fused-silica tubing with the diol polymer [poly(methylvinylsiloxanediol)] mixed with a silane cross-linker (Fig. 7). The vinyl groups bonded to the surface are then used for the in situ polymerization of acrylamide. The linear polyacrylamide layer was further cross-linked with formaldehyde. With the cross-linked coating, the EOF was 150 times less than that of an uncoated fused-silica capillary. High efficiencies ("' 1 x 106 plates/m) were achieved for the separation of basic proteins at pH 4.4 and acidic proteins at pH 8. The stability of the coating at basic pH was excellent, as the reproducibility of migration times was less than 1% after 600 consecutive injections at pH 8.8.
