Anion-binding polymers are described. The anion-binding polymers in some cases are low swelling anion-binding polymers. In some cases, the anion-binding polymers have a pore volume distribution such that a fraction of the polymer is not available for non-interacting solutes above a certain percentage of the MW of the target ion for the polymer. In some cases, the anion-binding polymers are characterized by low ion-binding interference, where the interference is measured in, for example, a gastrointestinal simulant, relative to non-interfering buffer. Pharmaceutical composition, methods of use, and kits are also described.