The effect of the aqueous solution pH and ligand type (H2PO4-, HPO42-, H2CO3, HCO3 (-), Cl-, and ClO4-) on acridine adsorption to silica was studied in a series of continuous-flow column experiments. The extent of acridine adsorption at solution pH’s above its pK(a) was enhanced when H2CO3/HCO3- was used as a buffer rather than H2PO4-/HPO42-, due to more exothermic hydration enthalpy of the H2CO3/HCO3- buffer. The greater polarity of the acridinium cation and/or acridinium cation/ligand complexes at solution pH’s below the pK(a) of acridine minimized the effect of differences in ligand hydration enthalpies on acridine adsorption. These results suggest that acridine mobility in groundwater would be buffer dependent.