Sorption mechanisms of cephapirin, a veterinary antibiotic, onto quartz and feldspar minerals as detected by Raman spectroscopy

Raman spectroscopy was used to investigate sorption mechanisms of cephapirin (CHP), a veterinary antibiotic, onto quartz (SiO(2)) and feldspar (KAISi(3)O(8)) at different pH. Sorption occurs by electrostatic attraction, monodentate and bidentate complexation. The zwitterion (CHP(o)) adsorbs to a quartz((+)) surface by electrostatic attraction of the carboxylate anion group (-COO(-)) at low pH, but adsorbs to a quartz((-)) surface through electrostatic attraction of the pyridinium cation, and possibly COO(-) bridge complexes, at higher pH. CHP(-) bonds to quartz((-)) surfaces by bidentate complexation between one oxygen of -COO(-) and oxygen from carbonyl of an acetoxymethyl group. On a feldspar((+/-)) surface, CHP(o) forms monodentate complexes between C=O, and possible -COO(-) bridges and/or electrostatic attachments to localized edge (hydr)oxy-Al surfaces. CHP(-) adsorbs to feldspar((-)) through monodentate C=O complexation. Similar mechanisms may operate for other cephalosporins. Results demonstrate, for the first time, that Raman techniques can be effective for evaluating sorption mechanisms of antibiotics. (C) 2009 Elsevier Ltd. All rights reserved.