Effect of Alkylammonium Salts

In these separations, use of a moderately high concentration of an alkylammonium salt in the electrolyte again adds a chromatographic component to CE. Sample anions migrating electrophoretically toward the detector are slowed by transient association with alkylammonium cations moving in the opposite direction. 

This association is considered to result from a combination of ion-ion and dispersive interactions. The following equilibrium is established  

This can be viewed as a dynamic equilibrium in which the anion spends a certain time fraction migrating as the free anion and another time fraction as the association complex, during which migration is much slower. The magnitude of this effect is a function of the type and concentration of the electrolyte cation, the counter-anion and of the properties of the analyte anion. 

5 = 2-naphthalenesulfonate. (A) tetraethylam-monium chloride (B) tetrapropylammonium chloride (C) tetrabutylammonium chloride (from Ref[17]with permission). 

2-naphthoquinone-4-sulfonate, salicylate, 2-naphthalenesulfonate, 1 -naphthalenesulfo-nate (from Ref. [18]). 

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