Chiral Microemulsion Electrokinetic Chromatography - Chiral Separations by Capillary Electrophoresis - page 246

O

H

O N

OH

H

CH(CH 3 ) 2

O

R -Dodecoxycarbonylvaline ( R -DDCV)

O

H

O N

OH

CH(CH 3 ) 2

O H

S -Dodecoxycarbonylvaline ( S -DDCV)

FIGURE 9.4 Structures of the chiral surfactant dodecoxycarbonylvaline (DDCV).

electrokinetic chromatography (MEKC) using the same chiral surfactant. Importantly,
the elution range with MEEKC was found to be approximately 2.5-fold greater than that
in MEKC. MEEKC enantioselectivities were slightly larger than those with MEKC
while efi ciencies were lower, resolution remained essentially unchanged, and reten-
tion factors were more optimal in the MEEKC mode. Subsequent to this publication,
it was determined that the lower efi ciencies resulted from the buffer identity [23].
A dramatic decrease in analysis time with a microemulsion PSP instead of micelles
was demonstrated for ephedrine and methylpseudoephedrine enantiomers (4 min
runtime, three times shorter than MEKC, see Figure 9.5). Elution order reversal was
easily accomplished by simply switching the stereochemical coni guration of the
surfactant as both forms are commercially available.

mAU

A1

40

A2

B1

35

30

25

B2

20

15

10

t 0

5

0

0.5 1 1.5 2 2.5 3 3.5 4 4.5min

FIGURE 9.5 Separation of enantiomers of methylpseudoephedrine and ephedrine. (A1)
R , R -methylpseudoephedrine, (A2) S , S -met hylpseudoephed r i ne, ( B1) R , S -ephedrine, (B2)
S , R -ephedrine. Microemulsion system—1.0% (w/v) ( S )-DDCV, 0.5% (v/v) ethyl acetate,
1.2% (v/v) 1-butanol, 50 mM ACES buffer, pH 7.0, and a separation voltage of 18 kV. (From
Pascoe, R. and Foley, J.P., Analyst , 127, 710, 2002. With permission.)