Assessment of the chromatographic lipophilicity of eight cephalosporins on different stationary phases
The retention behaviors were investigated for a series of eight cephalosporins in thin-layer chromatography (TLC) using stationary phases of RP-2, RP-8, RP-18, –NH2, –DIOL, and –CN chemically bonded silica gel. Additionally, various binary mobile phases (water/methanol and water/acetone) were used in different volume proportions. The retention behavior of the analyzed molecules was defined by RM0 constant. In addition, reversed phase high performance liquid chromatography (RP-HPLC) was performed in lipophilicity studies by using immobilized artificial membrane (IAM) stationary phase. Obtained chromatographic data (RM0 and logk'IAM) were correlated with the lipophilicity, expressed as values of the log calculated (logPcalc) and experimental (logPexp(shake-flask)) partition coefficient. Principal component analysis (PCA) was applied in order to obtain an overview of similarity or dissimilarity among the analyzed compounds. Hierarchical cluster analysis (HCA) was performed to compare the separation characteristics of the applied stationary phases. This study was undertaken to identify the best chromatographic system and chromatographic data processing method to enable the prediction of logP values. A comprehensive chromatographic investigation into the retention of the analyzed cephalosporins revealed a similar behavior on RP-18, RP-8 and –CN stationary phases. The weak correlations obtained between experimental and certain computed lipophilicity indices revealed that RM0 and PC1/RM are relevant lipophilicity parameters and the RP-8, –CN and RP-18 plates are appropriate stationary phases for lipophilicity investigation, whereas computational approaches still cannot fully replace experimentation.