A new easy-to-prepare homogeneous continuous electrochromatographic bed for enantiomer recognition

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"?).