DETERMINATION OF LIPOPHILICITY BY MEANS OF REVERSED-PHASE THIN-LAYER CHROMATOGRAPHY .2. INFLUENCE OF THE ORGANIC MODIFIER ON THE SLOPE OF THE THIN-LAYER CHROMATOGRAPHIC EQUATION

The R(M) values measured for a series of steroids were very close to those determined more than 15 years ago using the same chemicals. This finding supports the reliability of R(M) values as a lipophilicity parameter. However, the point at issue in this work was the influence of the organic solvent in the mobile phase on the slopes of the TLC equations. In fact, the slopes of the TLC equations were shown to be related to the reciprocal of the solvent strength (1/E(0)). As a consequence, the ratio between the slopes of the TLC equations in different solvent systems are close to the ratio between the 1/E(0) values for the corresponding solvent pairs. A further interesting aspect seems to arise from the analysis of the equations correlating slopes and intercepts of the TLC equations. In particular, the ratios between the b values of such equations in different solvent systems are close to the ratios between the corresponding E(0) values.