Revisiting thin-layer chromatography as a lipophilicity determination tool. Part II — Is silica gel a reliable adsorbent for lipophilicity estimation?
Ewelina Gowin, Łukasz Komsta · Journal of Planar Chromatography – Modern TLC · 2012
Lipophilicity is often estimated by thin-layer chromatography (TLC) as a fundamental property related to biological and pharmaceutical activity. In a recent study, we contributed some standardization to the subject by performing a comparative analysis of the different approaches in the field. This part presents an analogous study on silica, the use of which in normal-phase systems seems to be a new trend of recent times. We have compared several approaches of TLC lipophilicity determination: a single TLC run, Soczewiński-Wachtmeister equation coefficients, principal component analysis (PCA) of the retention matrix, and PARAFAC on a three-way array. All techniques were applied to 35 model solutes with simple molecules, using nine concentrations of six modifiers: acetone, dioxane, ethyl acetate, methylethylketone, propan-2-ol, and tetrahydrofuran. Comparative analysis points to several general recommendations. Ethyl acetate seems to give the best correlations with lipophilicity, and the correlations of single retention values, extrapolated values (intercepts), or C0 are satisfactory (around 0.8) to use in normal-phase method in lipophilicity estimation. However, the correlation is quite worse and the normal-phase method should be treated as a method supplementary to the reversed-phase method. Neither PCA nor PARAFAC carried out on the retention matrix improved the correlations.