Biomedical Engineering Reference
In-Depth Information
2
Eutomer (R)
1.5
Distomer (S)
1
0.5
0
10
10.5
11
Time (min)
11.5
12
FIGURE 4.5
Quantii cation of the enantiomeric impurity at the 0.1% level. Conditions:
fused-silica capillary, 50 cm total length (41.5 cm effective length) × 50 μm, i.d.; electrolyte,
100 mM H
3
PO
4
/triethanolamine (pH 3) + 7.5 mM DM-β-CD + 3 mM CM-β-CD; voltage,
+25 kV; temperature, 25°C; detection, 214 nm; hydrodynamic injection 20 s at 50 mbar pre-
ceded by a water-plug preinjection for 5 s at 30 mbar; [
R
]: 200 μg/L; [
S
]: 0.2 μg/L. (Reprinted
from Lorin, M. et al.,
Anal. Chim. Acta
, 592, 139, 2007. With permission.)
to strongly increase the enantioselectivity. The careful optimization of the nature
and concentration of both CDs, as well as the applied voltage and the injection time,
allowed the authors to separate (
R
s
= 7.2) in short analysis time and quantify success-
fully 0.05% of enantiomeric impurity, even if the impurity was migrating after the
major enantiomer (cf. Figure 4.5).
Since many parameters may inl uence the enantioselectivity, Danel et al. used
a chemometric approach to i nd optimal conditions for the enantioselective analy-
sis of an antipsychotic and its main metabolite [24]. They used a central composite
design through the response surface methodology to maximize enantioresolution,
i nding optimal CDs (sulfated-
-CD) and phosphate buf-
fer concentrations. The linear and quadratic coefi cients for the three factors were
all signii cant but no interactions were found. This methodology was successfully
applied and the method was validated according to the acceptance criteria of ICH.
The perspectives would be to undertake the metabolism study of this antipsychotic
in biological media.
Recently Chu et al. validated successfully the assay of a chiral antiparkinso-
nian drug (rotigotine) and its chiral impurities [38]. They i rst tried single CD sys-
tems (
α
-CD and hydroxypropyl-
β
-CD), but they could not separate rotigonine and
related impurities simultaneously. However, they observed a synergistic effect
and complete separation using a dual CD system made of S-
β
-CD, S-
β
-CD or methyl-
β
β
-CD and methyl-
β
-CD in an acidic BGE (pH = 2.5). The optimal concentration for both S-
β
-CD
and methyl-
-CD was found to be 2% (w/v), taking enantioresolution and migration
times into consideration (total analysis time: 15 min). They also observed that the
increase in the BGE ionic strength is favorable to enantioresolution due to the
reduction of the EOF and the increase in buffer viscosity. Then method validation
was performed evaluating specii city, precision, linearity, sensitivity, and accu-
racy. Finally, they applied the method to estimate the impurities of i ve batches
of rotigotine.
β
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