Capillary electrophoresis using core-based hyperbranched polyethyleneimine (CHPEI) static-coated capillaries

With unique 3-D architecture, the application of core-based hyperbranched polyethyleneimine (CHPEI), as a capillary coating in capillary electrophoresis, is demonstrated by manipulation of the electroosmotic mobility (EOF). CHPEI coatings (CHPEI5, M(w) approximately 5000 and CHPEI25, M(w) approximately 25,000) were physically adsorbed onto the inner surface of bare fused-silica capillary (BFS) via electrostatic interaction of the oppositely charged molecules by rinsing the capillaries with different CHPEI aqueous solutions. The EOF values of the coated capillaries were measured over the pH range of 4.0-9.0. At higher pH (pH >6) the coated capillary surface possesses excess negative charges, which causes the reversal of the EOF. The magnitudes of the EOF obtained from the coated capillaries were three-fold lower than that of BFS capillary. Desirable reproducibility of the EOF with % RSD (n = 5) < or = 2 was obtained. Effect of ionic strength, stability of the coating (% RSD = 0.3) and the dependence of the EOF on pH (% RSD = 0.5) were also investigated. The CHPEI-coated capillaries were successfully utilized to separate phenolic compounds, B vitamins, as well as basic drugs and related compounds with reasonable analysis time (< 20 min) and acceptable migration-time repeatability (< 0.7% RSD for intra-capillary and < 2% RSD for inter-capillary).