Aqueous phase adsorption of certain beta-lactam antibiotics onto polymeric resins and activated carbon

The adsorption of certain beta-lactam antibiotics such as 7-aminocephalosporanic acid, cephalexin, cefadroxyl and 6-aminopenillanic acid in aqueous solution has been studied using polymeric resins of four different types as well as activated carbon. The adsorption intensity was found to be strongly dependent on the aqueous phase pH and this dependence could be interpreted from a model for neutral species adsorption in all cases. Adsorption equilibrium data were correlated with the Langmuir, Freundlich and Redlich-Peterson isotherm, the Langmuir model being found to provide the best fit of the experimental data. The differences in adsorption affinities of the solute obtained for the different adsorbents were interpreted from sorbent surface chemistry and morphological structure. From the correlation obtained between adsorption affinity and estimated enthalpy, it may be predicted that the adsorption is determined by a specific solute-sorbent interaction which is predominantly of enthalpic type. The adsorption rate curves for almost all the solutes appear to be typical of the first order kinetics. However, more precise kinetics will require inclusion of the external mass transfer effect initially and particle diffusion effect at a later stage. (C) 1999 Elsevier Science B.V. All rights reserved.