Biomedical Engineering Reference
In-Depth Information
TABLE 14.2
Particulate CSPs Evaluated in CEC Enantiomer Separations
CSP
Ref.
Coated polysaccharide
CSPs (Figure 14.8a)
[20,54,55,63-65,111-119]
Including cellulose tris(3,5-dimethylphenylcarbamate)
(Chiralcel OD), amylose tris(3,5-dimethylphenylcarbamate)
(Chiralpak AD), cellulose tris(4-methylbenzoate)
(Chiralcel OJ), cellulose tris(3,5-dichlorophenylcarbamate),
cellulose tris(3-chloro-4-methylphenylcarbamate)
Immobilized polysaccharide
CSPs (Figure 14.8b)
[21,66,67]
Protein
CSPs
[107,108]
Macrocyclic antibiotics
CSPs
including vancomycin (Figure 14.9a)
[19,61,120-124]
teicoplanin (Figure 14.9b)
[60,62,125,126]
teicoplanin aglycone (Figure 14.9b)
[36,127]
Cyclodextrin
CSPs (e.g., Figure 14.10)
[31,32,39,110,128-132]
Donor-acceptor
(Pirkle-type) CSPs (e.g., Whelk O 1;
see Figure 14.4)
[35,133-137]
Chiral ion-exchangers
Chiral anion-exchangers (e.g., Figure 14.2a)
[17,22,102,138]
Chiral cation-exchangers (e.g., Figure 14.2b)
[23,24,139-141]
longer packed columns can be used (typical 25 cm) than in standard HPLC with 3
m
particles. (Note, UPLC was not available when CEC technology was developed;
hence this was a striking argument.) Together with less l ow maldistribution, i.e.,
a reduced
A
-term contribution to band broadening, as well as a relaxed-mass trans-
fer resistance (smaller
C
-term leading to l atter
H
-
u
curves) 3.5
μ
m particles lead
to greatly improved separation efi ciencies in CEC. 30-75,000 theoretical plates
per column of 25 cm length can readily be obtained as already mentioned before
[24,126,140]. Unfortunately, common CSPs like polysaccharide-based CSPs, mac-
rocyclic antibiotics CSPs were formerly commercially available only as 5
μ
μ
m beads
and only since recently as 3
m beads as well.
Enantiomeric separation deals with low molecular mass compounds and hence
virtually all CSP particles but the polysaccharide CSPs are based on silica beads
with about 100 Å pore diameter. This pore diameter is appropriate for most separa-
tions and has the advantage of a large surface area and high adsorption capacity
which may be required in analytical separations as well, e.g., when overloading is
necessary to detect trace enantiomeric impurities [140].
However, for the coating of polysaccharide-type biopolymers onto the support
surface wide pore silica (1000-4000 Å) appears to be advantageous because the risk
for clogging of intraparticulate pores in the course of the coating step is reduced. In
such wide pore materials, convective l ow in the mesopores may favorably contribute
to the l ow characteristics and dynamics in CEC and lead to an enhancement of rela-
tive EOF velocities and mass transfer through convection [54]. In fact, electroosmotic
μ
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