Experimental determination of ampicillin adsorption to nanometer-size Al2O3 in water

Transport of antibiotics in soil–water systems is controlled in part by adsorption to nanometer-size (10−9 m) particles. Batch adsorption experiments were performed with ampicillin, a common amphoteric antibiotic, and 50 nm-Al2O3 (α-alumina) at different pH conditions. Sorption to Al2O3 can be described by linear isotherms for 2.9 μM–2.9 mM ampicillin concentrations. Distribution coefficients (Kd) are 11.1 (±0.32) L kg−1 at pH 2, 0.55 (±.04) L kg−1 at pH 4, 21.9 (±0.9) L kg−1 at pH 6, and 39.5 (±2.2) L kg−1 at pH 8. At pH 2, ∼47% of the initially adsorbed drug was removable by rinsing, at pH 4–56% was removed. Only 7% of the drug could be removed by rinsing at pH 6, and 3% at pH 8. Weak electrostatic forces dominate at pH < 4, and stronger attachment mechanisms at higher pH. Low yields in rinsing (desorption) experiments at pH ⩾ 6 indicate strong attachment mechanisms, either electrostatic or possibly surface complexation.