Fused silica capillaries treated with dilute solutions of high molecular weight polyarginine (PA) provide capillary electrophoresis separation efficiencies of more than 2 million theoretical plates per meter and improved migration time reproducibility for the analysis of protein mixtures. The non-covalently bound PA coating was stable for several days and could be easily regenerated by exposing the capillary to a dilute solution of PA for several minutes. A comparison of PA and polybrene (PB) treated capillaries indicates that the PA capillary is capable of providing higher separation efficiencies, but that PB provides a more stable coating when used under acidic conditions and with high ionic strength buffers.