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-Al(2)O(3) (alpha-alumina) at different pH conditions. Sorption to Al(2)O(3) can be described by linear isotherms for 2.9 microM-2.9 mM ampicillin concentrations. Distribution coefficients (K(d)) 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, approximately 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 pH6 indicate strong attachment mechanisms, either electrostatic or possibly surface complexation.