A capillary electrokinetic chromatography technique is described that employs neutral cyclodextrins (CDs) as a primary phase, transported with electroosmotic flow, and charged CDs as an electrophoretically mediated secondary phase. Neutral, hydrophobic solutes are separated on the basis of their differential distribution between these CD phases. The technique resembles micellar electrokinetic capillary chromatography (MECC) with regard to instrumentation and the fundamental relationships for resolution and capacity factor, which are influenced by the existence of a finite elution window. Conversely, the CD technique offers unique and beneficial characteristics when compared to MECC. Efficiency, selectivity, and system retention are evaluated on the basis of separations of polyaromatic hydrocarbons (PAHs). mciency is comparable to that of MECC (> lo5 platedm). The specificity associated with solute-CD inclusion complexation provides elution orders for PAHs that do not follow the hydrophobicity trends of MECC. Moreover, since the CD phases are largely noninteractive, complex CD systems can be used to enhance selectivity. Capacity factors can be altered in a convenient and predictable fashion simply by changing the CD phase ratio. The technique is rather robust with regard to the use of running buffers containing organic solvents; the effects or organic modifier and pH on system retention are demonstrated.

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Studies of pyrene complexes with /8-cyclodextrln, using reversed-phase (C1t) liquid chromatography require a relatively more nonpolar mobile phase than water (mixtures of methanol-water >55 % methanol) In order to achieve a reasonable retention time. Although methanol has a very low association constant with 8-cyclodextrin, It becomes strongly competitive at high concentrations, resulting In very weak Interaction between pyrene and cyclodextrin. The presence of /erf-butyl alcohol or cyclopentanol hi the medium Increases the strength of the /8-cyclodextrin-pyrene complex by various orders of magnitude due to the formation of a ternary complex. In the presence of these alcohols as mobile-phase comodifiers, the Interaction between 8-cyclodextrln and pyrene becomes evident at methanol concentrations In the range of practical use for HPLC.

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