Lipophilicity measurement of nicotinates by reversed-phase high-performance liquid chromatography : Differences in retention behaviour, but similarities of log kw values, in methanol-water and acetonitrile-water eluents

Abstract

The lipophilicity of 22 nicotinate esters was examined by reversed-phase high-performance liquid chromatography using methanol-water and acetonitrile-water as eluents. In the former system, a linear relationship exists between the log of the capacity factor (log k) and the fraction of modifier in the eluent. In contrast, the relationship is parabolic in the acetonitrile-water system. This behaviour is interpreted in terms of parabolic in the acetonitrile-water system. This behaviour is interpreted in terms of a dual retention mechanism, namely hydrophobic expulsion and polar (presumably silanophilic) interactions. Linear (methanol-water) and parabolic (acetonitrile-water) extrapolations to 0% modifier yielded practically identical log k w values ( r 2 = 0.980), indicating that for a given stationary phase, log k w is an index of hydrophobic effects independent of specific solute-modifier interactions. The log k w values correlate well with calculated log P oct values ( r 2 = 0.962 and 0.948).