Optimization of separation and migration behavior of cephalosporins in capillary zone electrophoresis

The influences of buffer pH, buffer concentration and buffer electrolyte on the migration behavior and separation of 12 cephalosporin antibiotics in c apillary zone electrophoresis using three different types of buffer electro lyte, including phosphate, citrate, and 2-(N-morpholino)ethanesulfonate (ME S), were investigated. The results indicate that, although buffer pH is a c rucial parameter, buffer concentration also plays an important role in the separation of cephalosporins, particularly when cefuroxime and cefazolin, c ephalexin and cefaclor, or cefotaxime and cephapirin are present as analyte s at the same time. The electrophoretic mobility of cephalosporins and elec troosmotic mobility measured in citrate and MES buffers are remarkably diff erent from those measured in phosphate buffer. With citrate buffer, optimum buffer concentration is confined to a small range (35-40 mM), whereas buff er concentrations up to 300 mM can be used with MES buffer. Complete separa tions of 12 cephalosporins could be satisfactorily achieved with these thre e buffers under various optimum conditions. However, the separability of 12 cephalosporins with citrate or MES buffer is better than that with phospha te buffer. As a consequence of a greater electrophoretic mobility of cephal osporins than the electroosmotic mobility with citrate buffer at pH below a bout 5, some cephalosporins are not detectable. The cloudiness of the peak identification and of the magnitudes of the electrophoretic mobility of cef otaxime and cefuroxime reported previously are clarified. In addition, the pK(a) values of cephradine, cephalexin, cefaclor, and cephapirin attributed to the deprotonation of either an amino group or a pyridinium group an rep orted, and the migration behavior of these cephalosporins in the pH range s tudied is quantitatively described. (C) 2000 Elsevier Science B.V. All righ ts reserved.