With their unique separation behaviors and tolerance for relatively high salt concentrations, mixed-mode resins have become important tools in the process developer’s toolbox. Here we provide an introduction to the modes of action of mixed-mode resins and a discussion of their general applications. We also provide guidelines on when to use mixed-mode resins and discuss important considerations for resin screening. Lastly, we describe two of Bio-Rad’s popular mixed-mode resins, Ceramic Hydroxyapatite (CHT™) and Nuvia™ cPrime™.
How Mixed-Mode Works
Mixed-mode — or multimodal — chromatography, as the name implies, utilizes two or more interaction principles for purification (see table below). These interactions may occur naturally, or the media supports may be functionalized with appropriate ligands. Strictly speaking, most of the common resins on the market today exhibit some degree of mixed-mode interactions. For example, in ion-exchange resins where the functional group is coupled via a spacer to the base bead, the spacer and/or the base bead can each contribute some hydrophobic interaction in addition to the ion exchange functionality of the pendant group. Such mixed-mode effects are responsible for the different behaviors of otherwise identical supports.