Study on the reactive extraction and stripping kinetics of certain β-lactam antibiotics

The extraction equilibrium and stripping of certain β-lactam antibiotics such as 7-aminocephalosporanic acid (7-ACA), 7-aminodeacetoxy cephalosporanic acid (7-ADCA), 6-aminopenicillanic acid (6-APA), cephalosporin-C (CPC) and cephalexin from aqueous solution of phosphate and carbonate buffers were studied with Aliquat-336 (tricaprylylmethylammonium chloride) dissolved in n-butylacetate as the solvent over an aqueous phase pH range of 5–10. The extraction equilibrium constant Kp was found to increase with aqueous phase pH, which is attributed to the increase in ionisation of the β-lactam. A systematic study on kinetic of stripping or re-extraction of 7-ADCA and cephalexin from the extracted phase was carried out using an aqueous solution of citrate buffer at different pH values and was found to be pH dependent which is also attributable to ionisation behaviour of the β-lactams. Such observation is considered important, as re-extraction at an appropriate pH value is possible. The rate of stripping was found to be weakly dependent on Cl− concentration of the aqueous phase and the same was analysed with a simple mass transfer model based on film theory.