Factors Influencing Cyclodextrin-Mediated Chiral Separations - Chiral Separations by Capillary Electrophoresis - page 93

6
5

6

4

3

5

2

1

4

0 0

1 2 3 4 5

HP-β-CD concentration (mM)

3

2

1

0 0

10 20 30 40 50 60

HP-β-CD concentration (mM)

Ketoconazole Terconazole Miconazole Sulconazole Econazole

FIGURE 4.2 Inl uence of the HP-β-CD concentration on the mobility differences
between the enantiomers of ketoconazole, terconazole, miconazole, sulconazole, and
econazole. (Reproduced from Castro-Puyana, M. et al., Electrophoresis , 28, 2667, 2007.
With permission.)

by Castro-Puyana et al., in a paper dealing with the chiral separation of six azole
compounds using a neutral CD ( β -CD, HP- β -CD, or heptakis-(2,3,6-tri- O -methyl)-

β -CD) [7]. A reversal of the migration order of ketoconazole and terconazole

enantiomers with HP- -CD concentration was observed compared to the other

CDs. As can be seen in Figure 4.2, the mobility difference of both compounds
enantiomers reached a maximum at low HP-

β

-CD concentrations, decreased down
to zero at 5 mM CD concentration, and then increased again at concentrations
higher than 5 mM for ketoconazole and 30 mM for terconazole. Apparent bind-
ing constants for the azole enantiomers with the three investigated CDs were also
determined.

β

4.3 BGE pH AND IONIC STRENGTH
In the case of ionizable CD derivatives, such as carboxymethyl- and carboxyethyl- -

CDs, it is obvious that the buffer pH inl uences the binding strength and the complex
mobility. As the pH determines the effective net charge and the effective mobility of
the complexes, it will affect the migration times, the shape, and the efi ciency of the
analytes' peaks, like in achiral CE systems [5].
Kirschner et al. developed a CE method with laser-induced l uorescence detec-
tion to resolve and determine the enantiomers of cyanobenz[ f ]isoindole (CBI)

β