Enantioseparations by Capillary Electrochromatography - Chiral Separations by Capillary Electrophoresis - page 440

14.8.3.3 Hybrid Monoliths from Particles
A third kind of monoliths are made from particles. They represent a hybrid form of
the above discussed packed and monolithic columns. Such monoliths have been i rst
described for enantioselective CEC by Lin and coworkers in 1996 in the form of cap-
illaries packed with MIP particles that were i xed with a polyacrylamide matrix [208]
and later by Chirica and Remcho who embedded MIP particles in a silicate matrix
[206]. In another early paper, Schurig's group proposed the consolidation of the chro-
matographic bed packed with silica beads by sintering the particles in the capillary
over the entire length [205]; the subsequent coating with selectors like Chirasil-Dex,
a dimethylpolysiloxane derivative bearing permethylated -cyclodextrin, furnished

an enantioselective monolithic column in a second step. The complexity of fabrica-
tion of the latter type of column prevented its further consideration.
Two other concepts, however, attracted more interests. In one, the station-
ary phase particles are slurry packed into the capillary and the packing is then
stabilized in the capillary by a sol-gel or polymer matrix. If silica particles are
used, the particles may be i xed (glued together at their contact points) through
co-condensation of residual silanols with the sol-gel matrix (Figure 14.23a) or

β

(b)

(a) (c)

FIGURE 14.23 SEM images of hybrid monoliths: (a) Chira-Dex-silica particle-glued
monolith. Magnii cation, 800 × (top) and 10,000 × (bottom). (Reprinted from Wistuba, D.
et al., Electrophoresis , 26, 2019, 2005. With permission.) (b) Particle-loaded polyacrylamide-
based monolith. (Reprinted from Schmid, M.G. et al., Electrophoresis , 25, 3195, 2004. With
permission.) (c) ROMP-based monolithic stationary phase. (Reprinted from Gatschelhofer, C.
et al., J. Biochem. Biophys. Methods , 69, 67, 2006. With permission.)