EVALUATION OF A DUAL-CYCLODEXTRIN PHASE VARIANT OF CAPILLARY ELECTROKINETIC CHROMATOGRAPHY FOR SEPARATIONS OF NONIONIZABLE SOLUTES

A capillary electrokinetic chromatography technique is described that employs neutral cyclodextrins (CDs) as a primary phase, transported wi th electroosmotic flow, and charged CDs as an electrophoretically medi ated secondary phase. Neutral, hydrophobic solutes are separated on th e basis of their differential distribution between these CD phases. Th e technique resembles micellar electrokinetic capillary chromatography (MECC) with regard to instrumentation and the fundamental relationshi ps for resolution and capacity factor, which are influenced by the exi stence of a finite elution window. Conversely, the CD technique offers unique and beneficial characteristics when compared to MECC. Efficien cy, selectivity, and system retention are evaluated on the basis of se parations of polyaromatic hydrocarbons (PAHs). Efficiency is comparabl e to that of MECC (>10(5) plates/m). The specificity associated with s olute-CD inclusion complexation provides elution orders for PAHs that do not follow the hydrophobicity trends of MECC. Moreover, since the C D 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 tec hnique is rather robust with regard to the use of running buffers cont aining organic solvents; the effects. or organic modifier and pH on sy stem retention are demonstrated.