Mj. Sepaniak et al., EVALUATION OF A DUAL-CYCLODEXTRIN PHASE VARIANT OF CAPILLARY ELECTROKINETIC CHROMATOGRAPHY FOR SEPARATIONS OF NONIONIZABLE SOLUTES, Analytical chemistry, 67(13), 1995, pp. 2037-2041
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.