Functionalized substrates with ion-exchange properties

Abstract

The current invention provides compositions, which are useful as stationary phases for a variety of chromatographic applications, such as high performance liquid chromatography (HPLC) and solid-phase extraction (SPE). The compositions include a porous solid support (e.g., silica gels, silica monoliths or synthetic organic resins) having an exterior surface and pore openings defined by 'interior walls'. To the solid support are covalently bound organic ion-exchange ligands (e.g., silyl ligands), which incorporate at least one ion-exchange group (e.g., ionic or ionizable group). The compositions further include micro-particles (e.g., latex particles) incorporating ion-exchange groups having a charge that is opposite to the charge found on the support. The micro-particles are bound to the exterior surface of the support (e.g., via electrostatic forces). The micro-particles have a size that is sufficient to minimize the number of particles that can enter the pores of the support thereby reducing or essentially preventing binding of the micro-particles to the interior walls of the pores. While the pores are essentially too small for the micro-particles, they can still be accessed by the analytes present in a chromatographic sample. The physical separation of ion-exchange groups located within the pores and the surface of the micro-particles, respectively, prevents reactions (e.g., formation of salt-bridges) between the oppositely charged groups and provides compositions with both anion-exchange and cation-exchange capabilities within the same stationary phase. The ligands bound to the solid support can optionally include additional (e.g., reverse-phase) functionalities creating multi-modal (e.g., trimodal) stationary phases.