Zone formation in ion-pair RPLC I. Effects of adsorption of organic ions on established column equilibria

Summary Adsorption of organic ions to Bondapak Phenyl from a water-based mobile phase was studied by the breakthrough technique. The adsorption of decanesulfonate as sodium ion pair as well as of an organic cation, dimethylprotriptyline, as phosphate ion pair was best fitted to a two-site ion-pair adsorption model of the Langmuir type indicating a heterogenous solid phase surface. Introducing an organic ion into a column in equilibrium with an organic ion of opposite charge created negative zones due to increased adsorption of the second ion. The positions of the beginning and the end of the zone were dependent of the concentrations of the two organic ions in the system.