The comparison of tocopherol isomer separation achieved using different stationary-phase alkyl chain lengths (i.e., C18 vs C30) and modes of alkyl phase attachment to the silica-based supports (i.e., polymeric vs monomeric synthesis) using capillary electrochromatography (CEC) has been demonstrated. The smaller alkyl chain does not exhibit the shape selectivity needed to resolve all of the tocopherol isomers. Conversely, both polymeric and monomeric C30 phases show increased tocopherol isomer selectivity. Changing the elutropic strength of the mobile phase had dramatic effects on the selectivity, with small additions of water to a methanol mobile phase yielding the best selectivity. The complete baseline separation of the tocopherol isomers was achieved using the monomerically bound C30 stationary phase and a methanol/ water mobile phase. The differences in stationary-phase selectivity were examined using a NIST standard reference material for determining column selectivity in LC. The results indicated that the monomeric C30 actually had "intermediate" phase characteristics (i.e., high phase loading, end capping, etc). This new CEC-based separation was also used to separate the tocopherols in a vitamin E supplement sample.

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Separation of cholesterol and its ester derivatives using micellar electrokinetic chromatography is a challenge due to the extreme hydrophobicity of these compounds. In this work, an isocratic capillary electrochromatography (CEC) method has been developed to separate a complex mixture of cholesterol and its 12-ester derivatives. The proportions of mobile phase (tetrahydrofuran, acetonitrile, water), as well as the effects of acid modifiers, buffer concentrations, voltage, and temperature on the separation of cholesterol derivatives were investigated. Addition of a polymeric surfactant, poly(sodium N-undecanoyl-L-glycinate), to the mobile phase reduced migration time and improved resolution of the analytes. The CEC method developed allows baseline separation of a complex mixture of cholesterol and 12 ester derivatives in less than 40 min. Finally, the method is applied to the characterization of cholesterol, cholesterol linoleate, and cholesterol oleate extracted from atherosclerotic plaque deposits in the arterial walls of a human aorta.

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