Stationary phases based on a reversed phase retention mechanism have long been the mainstay of HPLC. However, ion exchange materials have very gradually been increasing in prominence in HPLC. Currently, ion exchange is the second most commonly used retention mechanism after reversed phase in HPLC. More recently, high-performance mixed-mode ion exchange phases have been an area of focus in the development of ion exchange materials for HPLC. New bi-mode and tri-mode phases have been developed that allow independent retention control for analyte classes, affording unparalleled flexibility in method development for complex mixtures.
In addition, ion exchange materials have been the mainstay from the inception of ion chromatography. Here, mobile phases utilizing extremes in pH are the norm. As such, polymeric ion exchange materials with vastly superior pH stability play a dominant role when it comes to stationary phases utilized in ion chromatography. Stationary phases used in ion chromatography utilize a wide variety of different architectures including pellicular structures with nonporous substrates as well as fully porous substrates. Stationary phases are attached to such substrates utilizing a variety of different methods including electrostatic attachment, radical grafting and condensation polymerization.
In this work we will illustrate recent progress in the development of advanced polymeric as well as silica-based ion exchange materials useful for ion chromatography and HPLC. Included will be examples demonstrating the potential of such materials and their use specific application areas in both ion chromatography and HPLC. Examples will include stationary phases with “pure” ion exchange retention as well as mixed-mode ion exchange where ion exchange is combined with reversed phase, HILIC or a complementary ion exchange retention mechanism.