Separation selectivity patterns in the capillary electrophoretic separation of anionic enantiomers by octakis-6-sulfato-gamma-cyclodextrin

The capillary electrophoretic separation of anionic enantiomers with multip ly-charged, single-isomer, anionic resolving agents was reexamined with the help of the charged resolving agent migration model. Three general model p arameters were identified that influence the shape of the separation select ivity and enantiomer mobility difference curves: parameter b, the binding s electivity (K-RCD/K-SCD). parameter s, the size selectivity (mu (0)(RCD)/mu (0)(SCD)), and parameter a, the complexation-induced alteration of the ana lyte's mobility (mu (0)(SCD)/mu (0)). Function analysis of the model indica tes that there are six unique separation selectivity vs. resolving agent co ncentration patterns: in two of the patterns, separation selectivity asympt otically increases to the limiting: value set by parameter b; in two other patterns, separation selectivity passes a local maximum and asymptotically decreases to the limiting value set by parameter B; and in the last two pat terns, separation selectivity passes a Local maximum, decreases to unity, t hen, after reversal of the intrinsic migration order, asymptotically increa ses to the limiting value set by parameter b. Though the patterns with asym ptotically increasing selectivities were observed in earlier work, this pap er reports the first experimental verification of the existence of the loca l selectivity maximum during the capillary electrophoretic separation of th e enantiomers of several weak acids in high pH background electrolytes with octakis-6-sulfato-gamma -cyclodextrin as the resolving agent.