RAMAN SPECTROSCOPIC INVESTIGATION OF CEPHALOSPORIN ANTIBIOTIC SORPTION ONTO SiO2, Al2O3, AND PLAGIOCLASE FELDSPAR

The widespread use of antibiotics and other drugs in animal agriculture, has resulted in the contamination of soils and natural waters, and generated an interest in the fate and transport of these pharmaceuticals in natural soil-water systems. The distribution and transport of these contaminants are a function of many factors, and can vary depending on mineralogy and related pH-dependent attachment mechanisms.

In this study, sorption mechanisms of two amphoteric cephalosporin antibiotics, cephapirin (CHP) and cefotaxime (CFT), onto SiO₂ (quartz), Al₂O₃ (corundum) and mixed SiO₂-Al₂O₃ plagioclase feldspar (oligoclase) were investigated by Raman spectroscopy. Vibrational mode assignments were based on ATR-FTIR analogues and Raman-FTIR comparisons. Results indicate that CHP^(-) attaches to a SiO₂^(-) surface via complexation of C=O carbonyl and –COO^- carboxyl groups. CHP^(-) and zwitterionic CHP^(o) are electrostatically attached, via the carboxylate anion (COO^-), to an Al₂O₃⁽⁺⁾ surface. Electrostatic attraction of COO^- also occurs to a positively-charged oligoclase surface at low pH, and to the positively-charged Al₂O₃⁽⁺⁾ and aluminol sites of a mixed +/- feldspar surface at near-neutral pH. CFT^(-) binds to SiO₂^(-) by –COO^- surface complexation, but CFT^(-) binds to Al₂O₃⁽⁺⁾ by surface complexation of the C=O of the acetyloxymethyl group.

Raman spectroscopy is proven to be useful for investigating antibiotic sorption to soil/aquifer materials. Data from this study indicate the key roles of the carboxyl and the carbonyl groups in cephalosporin adsorption. This mechanistic information is consistent, and somewhat comparable, with spectroscopic data obtained in previous studies of other antibiotics sorbing to SiO₂, Al₂O₃, and mixed SiO₂-Al₂O₃ materials.