Control of migration time window and selectivity in electrokinetic chromatography with mixed polymeric pseudostationary phases

Control of migration time windows and the improvement of separation were achieved by utilizing mixed polymeric pseudostationary phases in electrokinetic chromatography (EKC) in water-organic solvent mixtures. Polyallylamine (PAA)-supported pseudostationary phases, one with hexadecyl groups (PAA-C-16) with the shorter migration times and the other with decyl groups (PAA-C-10) with the longer migration times, enabled the control of migration time windows when used as a mixture. PAA-C-16 provided better separation for a region with relatively small k' values as in typical micellar EKC, while PAA-C-10 gave better separation for a region with relatively large k' values as in reversed-phase liquid chromatography, the mixture of the two PAA derivatives resulting in better overall separations for a wide range of hydrophobic compounds. The migration time of a solute is determined by the relative contribution of each pseudostationary phase to the partition of the solute in a mixed carrier system. A theoretical explanation was provided by assuming the contribution of the two polymeric pseudostationary phases working independently. The migration time of the effective (imaginary) pseudostationary phase was shown to be in between the actual migration times of the two carriers, and can be different for each solute depending upon the relative contribution of the two pseudostationary phases to the solute partition. (C) 1998 Elsevier Science B.V.