The preferential adsorption of the protonated form of weak bases by
montmorillonite causes an increase in the pKeff of
atrazine. The effect on the acid-base equilibrium of
atrazine is related to the exchangeable
cation on the surface of
montmorillonite. The greatest effect was produced by the presence of 3-hydroxypropylammonium-saturated
montmorillonite, which caused the pKeff of
atrazine to increase 5.3 units to 6.9. This shift in pKeff causes the protonated form of
atrazine to be the predominate species in the pH range encountered in the GI tract and should result in a high degree of adsorption of
atrazine. Fraction-bound studies confirmed this hypothesis by demonstrating virtually complete absorption of
atrazine by 3-hydroxypropylammonium-saturated
montmorillonite up to pH 6. The fraction-bound studies also verified that protonated
atrazine is adsorbed more completely by 3-hydroxypropylammonium-saturated
montmorillonite than by
bentonite USP or
sodium-saturated
montmorillonite. It is believed that saturation of the
clay surface by an organic
cation alters the surface environment of the
clay, which results in enhanced adsorption of the protonated form of
atrazine. The potential utility of
montmorillonite saturated with an organic
cation as an adsorbent for the
emergency treatment of
poisoning by weak bases is suggested.