Discrimination and direct determination of cephalosporins by circular dichroism.

The circular dichroism and ultraviolet spectra of 15 commercial cephalosporins in common clinical use are analyzed. Distinguishing between the beta-lactam antibiotics (penicillins, cephalosporins, and cephamycins) on the basis of their CD spectral data has been found to be straightforward. Furthermore, sufficient CD spectral dissimilarities are observed to discriminate among the cephalosporin homologues and to classify these antibiotics in five spectroscopic groups, on the basis of the wavelengths of their Cotton effects. In addition, some chemical structural characteristics for these spectroscopic groups are discussed. Besides molar absorptivity and CD data, the slopes and the intercepts of the equations of the regression line are calculated for each of these antibiotics, the correlation coefficients being higher than 0.9993. The validity of the proposed model is confirmed by analysis of the variance. The results demonstrated that the proposed method is accurate and precise. The method was successfully applied to the direct determination of these drugs in commercial oral suspensions, injections, and capsules. The principal advantages of this method are quickness and simplicity no derivatization or chromatographic separation steps being needed.