In which type of chromatography are proteins separated based on their charge?

Ion exchange chromatography is specifically designed to separate proteins based on their charge. This technique relies on the interaction between charged groups on the proteins and charged groups on the resin used in the chromatography column. Proteins will bind to the column based on their net charge at a given pH, allowing for their separation when a gradient of salt (or pH) is applied.

The specific interactions in this process make it highly effective for separating proteins with differing isoelectric points, as some proteins will have a stronger affinity for the resin and will elute at different salt concentrations, based on their charge characteristics.

Other chromatography methods serve different purposes: size exclusion chromatography separates molecules based on size, affinity chromatography relies on specific binding interactions, and reverse-phase HPLC focuses on hydrophobic interactions. Thus, the unique mechanism of ion exchange chromatography is what makes it the appropriate choice for separating proteins based on their charge.