Abstract The unique selectivity of mixed mode chromatography resins is increasing utilization of these novel selectivities into bioprocess applications. Developers of biopharmaceutical products need improved fundamental understanding of protein binding to these stationary phases to create efficient and robust purification processes. Four monoclonal antibodies and two model proteins were employed to characterize protein interaction with a mixed-mode chromatographic resin comprising a hydrophobic ligand with cation-exchange functionality. Binding of these proteins was studied as a function of salt concentration and pH in the presence of various mobile phase modulators. The resulting data was applied towards screening mobile phase modulators that could selectively decrease host cell protein levels during monoclonal antibody purification.