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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).

The micellar liquid chromatographic (MLC) separations of polycyclic aromatic hydrocarbons (PAHs) were optimized for three micellar systems, cetyltrimethylammonium chloride (CTAC), dodecyltrimethylammonium chloride (DTAC), and sodium dodecylsulfate (SDS), with 1-pentanol as the only organic additive. A difference in the separation was observed between CTAC and SDS/DTAC. Under each optimized separation conditions, CTAC-modified mobile phase provides the least desirable separation, which is attributed to its longer carbon tail (C16 vs. C12). In addition to 1-pentanol, the main organic additive, a second organic additive (3% 1-propanol) in the micelle-modified mobile phase was found to enhance the resolution of PAH chromatographic peaks. However, the extent of the enhancement varies for the different micellar systems, with the greatest resolution improvement seen for CTAC, and little effect for shorter-tail SDS and DTAC. This study shows the potential use of second organic additive (1-propanol), to the main nonpolar additive (1-pentanol), in facilitating the MLC separation of larger nonpolar compounds.