A. Vegvari et al., A new easy-to-prepare homogeneous continuous electrochromatographic bed for enantiomer recognition, ELECTROPHOR, 21(15), 2000, pp. 3116-3125
Completely homogeneous polyacrylamide-based gels were used for capillary el
ectrochromatography (CEC) of drug enantiomers. Like continuous beds (also c
alled continuous polymer rods, silica rods, monoliths) they do not require
frits to support the bed because it is covalently linked to the capillary w
all. A long lifetime is an important feature of the beds. The gel matrices
can be prepared in any laboratory and for specific interactions they can be
derivatized with appropriate ligands. The application range is, therefore,
broad. For chiral electrochromatography, negatively and positively charged
polyacrylamide gels copolymerized with 2-hydroxy-3-allyloxy-propyl-beta-cy
clodextrin (allyl-beta-CD) were prepared. The latter monomer was synthesize
d from beta-CD and allyl-glycidyl ether by a very simple one-step procedure
. Eight acidic, neutral and basic drug compounds were resolved into their e
nantiomers, most of them with baseline separation. Interestingly, the resol
ution is independent of the electroendosmotic velocity, i.e., rapid analyse
s will not give low resolution. Upon increasing this velocity, the plate he
ight for the fast enantiomer did not change (or decreased slightly), wherea
s that for the slow enantiomer increased. Only the last term in the van Dee
mter equation contributed significantly to the total plate height. The comp
osition of the gel was chosen such that the "pores" became large enough to
guarantee a satisfactory electroendosmotic flow (EOF). This open gel struct
ure explains why acetone diffused as in free solution, Le., independently o
f the presence of the gel matrix. This finding also indicates that the sepa
ration of small molecules in polyacrylamide gels cannot be explained by "mo
lecular-sieving", but rather by some type of adsorption ("aromatic adsorpti
on"?).