Fig. 1. Hydrophobic ion pairing schematic. (A) Possible charged groups (left) and hydrophobic moieties (right) for a counterion. (B) Stoichiometric ion pairing between a cationic API (blue) and anionic counterion. (C) Non-stoichiometric ion pairing. (D) Reversible ion pairing due to inadequate binding or hydrophobicity.