Modelling and optimization of the electrokinetic chromatographic separation of mixtures of organic anions and cations using poly(diallydimethyl- ammonium chloride) and hexanesulfonate as mixed pseudostationary phases

Abstract

The separation of a series of aromatic carboxylic acids, sulfonates and opiates using electrokinetic chromatography employing a mixture of the soluble cationic polymer poly(diallydimethylammonium chloride) (PDDAC) and the amphiphilic anion hexanesulfonate as pseudostationary phases is described. In this system, the PDDAC pseudostationary phase interacts with the anionic analytes, whereas the hexanesulfonate pseudostationary phase interacts with the cationic analytes. A migration model has been derived which takes into account the ion-exchange (IE) interactions between the anions and the cationic PDDAC as well as the ion-pair (IP) interactions between the opiates and the hexanesulfonate. A further interaction between the combined PDDAC-hexanesulfonate complex and the more hydrophobic analytes is also evident and is accounted for in the model. Constants obtained by applying the model agreed well with the expected trends in IE affinities of the anions for PDDAC and also corresponded with the hydrophobic natures of the analytes. Optimization of the PDDAC and hexanesulfonate concentrations was performed using the normalized resolution product and minimum resolution product criteria. The minimum resolution product criterion proved to be most successful. An advantage of the described system is the improvement in peak shapes obtained after addition of hexanesulfonate to the electrolyte, resulting in increased plate numbers and better resolution. The system was very robust with mobilities varying by less than 2% over a period of days and on using different capillaries.

The importance of capillary electrophoresis, capillary electrochromatography, and ion chromatography in separations of inorganic ions

“…A soluble cationic polymer, e.g., poly(diallyldimethylammonium chloride), has been tested for the separation of inorganic and organic anions and cations [23]. The selectivity can be manipulated by the introduction of another mode of interaction -ion exchange.…”

“…Terabe and Isemura [22] introduced additions of soluble ionic polymers to the running buffer, providing a pseudostationary phase. A soluble cationic polymer, e.g., poly(diallyldimethylammonium chloride), has been tested for the separation of inorganic and organic anions and cations [23]. The selectivity can be manipulated by the introduction of another mode of interaction -ion exchange.…”

Separation of inorganic and small organic anions by CE using phosphonium‐based mono‐ and dicationic reagents

“…Double chained surfactants, namely didodecyldimethylammonium bromide, were studied and proved to provide more uniform planar dynamic coating of the capillary wall 28, 29. Also noteworthy is the use of cationic polymers 30–32. Zwitterionic surfactant additives possess interesting properties 33, 34 as they adsorb on fused silica surface and suppress EOF without its reversal.…”

Micellar electrokinetic chromatography with polyelectrolyte complexes as micellar pseudo-stationary phases

“…Zakaria et al [19] reported on the use of a mixture of a soluble cationic polymer poly(diallydimethylammonium chloride) (PDADMA) and a amphiphilic anion (hexanesulfonate) as a pseudo-stationary phase. A migration model was derived that takes into account the ion-exchange interactions between the anions and PDADMA as well as ion-pair interactions between the samples (opiates) and the hexanesulfonate.…”