Experimental Determination of Ampicillin Adsorption to Nanometer-size Al2O3 in Water

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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 (alpha-alumina) at different pH conditions. Sorption to Al2O3 can be described by linear isotherms for 2.9 mu m-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, similar to 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.