Lipophilicity determination of non-homologous series of nonionic surfactants by means of reversed-phase thin-layer chromatography.

The lipophilicity and specific hydrophobic surface area of 22 nonionic surfactants having different hydrophobic moieties have been determined by reversed-phase thin-layer chromatography using methanol as an organic modifier. RM values decreased linearly with increasing concentration of methanol. Both the lipophilicity and specific hydrophobic surface area of the surfactants decreased with increasing numbers of ethylene oxide groups per molecule. The significant correlation between the RM0 value and the specific hydrophobic surface area indicates that these surfactants can be considered as a homologous series of solutes independently of their structural inhomogeneity. Stepwise regression analysis suggested that the hydrophobic moieties are not entirely solvated and they are in a folded state in the eluents.