DETERMINATION OF THE HYDROPHOBICITY PARAMETER R(MW) BY REVERSED-PHASETHIN-LAYER CHROMATOGRAPHY

Experimental conditions were established that permit the determination of chromatographic lipophilicity parameters on the basis of thermodyn amically true R(M) values. The superiority of methanol as compared wit h other modifiers (e.g., acetonitrile) is substantiated; physico-chemi cal reasons are discussed. Solvent pH influences only the silanophilic effect; hence, with highly ionized structures, determination at neutr al pH is to be preferred. Extrapolation to modifier-free conditions (R (Mw) value) is essential to diminish the contribution of polar interac tions. Advantages and disadvantages of non-linear extrapolation proced ures are compared with linear regression. Correctly estimated R(Mw) va lues coincide numerically not only with log k(w), values, as theoretic ally expected, but also with partitioning data from the octanol-water system.