COLLOIDS AND A Colloidsand Surfaces SURFACES ELSEVIER A: Physicochemical and Engineering Aspects 127 (1997) 25-37 The adsorption of certain semi-synthetic cephalosporins on activated carbon M. Dutta, R. Baruah, N.N. Dutta *, A.C. Ghosh Chemical Engineering Division, Regional Research Laboratory, Jorhat, 785 006, India Received 15 May 1996; accepted 22 January 1997 Abstract The adsorption of semi-synthetic cephalosporins such as 7-aminocephalosporanic acid (7-ACA), cephalexin and cefadroxyl from aqueous solution has been studied using activated carbon as the adsorbent. The pH dependence of the adsorption intensity could be interpreted from a model for neutral-species adsorption. 7-ACA exhibited relatively low adsorption intensity compared to cephalexin and cefadroxyl, whose adsorption intensities were nearly equal. The adsorption isotherm for all the three could be interpreted from the Langmuir model with a reasonable degree of accuracy. The adsorption-rate curves for the cephalosporins exhibited identical patterns at pH 7-8. The concen- tration-time profiles generated for cephalexin in an agitated slurry system indicate that external film diffusion controls the solute uptake initially, and particle diffusion controls solute uptake in the later stages. © 1997 Elsevier Science B.V. Keywords." Activated carbon; Adsorption; Cefadroxy; Cephelexin; 7-aminocephalosporanic acid 1. Introduction In our recent review [1 ], various methods of the extraction and purification of cephalosporin anti- biotics were discussed. We have been studying liquid-membrane and adsorptive separation pro- cesses for the recovery of beta-lactam antibiotics from culture broth. Although reactive extraction using liquid membranes can provide attractive separation selectivity for beta-lactam antibiotics [2], their commercial potential is yet to be established. Adsorption chromatography, recom- mended for the extraction and purification of various hydrophilic bioproducts [3], can be competitive for beta-lactams, particularly the cephalosporin group of antibiotics [1]. Non-ionic polymeric resins, ion-exchange resins, activated * Correspondingauthor. 0927-7757/97/$17.00 © 1997ElsevierScienceB.V. All rights reserved. PII S0927-7757 (97)00062-9 carbon, molecular sieves, etc. have been suggested as adsorbents for the isolation of hydrophilic products [1,3]. Though ion-exchange recovery processes are well developed, a significant amount of commercially produced cephalosporin is iso- lated using neutral polymeric adsorbents compris- ing copolymers of styrene (or ethyl benzene) and divinylbenzene. Various polymeric resins have therefore been studied for the preparative and analytical-scale isolation of cephalosporins [4-8]. The first adsorbent used was activated carbon, but regeneration problems make its use inappropriate in several cases. However, because of its low cost and easy availability, it does have prospects for use in the purification of cephalosporins, particu- larly at low pH conditions, under which cephalo- sporins are markedly hydrophobic [9]. Activated carbon has also been used for the efficient recovery of a semi-synthetic cephalosporin (i.e. cephalexin)