Experimental and theoretical investigation of high- concentration elution bands in ion-pair chromatography

The effective separation of many solutes, including pharmaceuticals, can be performed using an ion-pair reagent (IPR) in the mobile phase. However, chromatographic and mathematical modelling are a challenge ionpair chromatography (IPC), especially preparative mode, due to complicated process. In this study, we present retention mechanism model that predict overloaded concentration profiles IPC system with X-Bridge C18 as stationary phase tetrabutylammonium bromide 0 - 15 mM range IPR. Two different phases were used: (i) 15/85 [v/v] acetonitrile/water, (ii) 25/75 methanol/water. compounds sodium salts organic sulfonic acid functions. analytical elution obtained for specified conditions. data utilized calculate difference electrical potential between surface bulk solution firm electrostatic theory. mode certain IPR concentrations, U-shaped observed. other considered cases, Langmuir recorded. A multilayer adsorption was derived, which is consistent dynamic ion exchange models. assumes lipophilic adsorbs on phase, creating charged active sites serve solutes. molecules solute adsorb already formed layer. It also assumed subsequent layer form complexes interactions molecules. takes into account attraction repulsion molecules, depending situation. proposed allowed prediction very good agreement followed progression from Langmuirian, through U-shaped, again Langmuirian profiles.