Abstract
Partition coefficients (P) of pyrazine and its COOMe derivative (strong hydrogen bond acceptor), were measured for the octane/aqueous methanol partitioning system (PO/M-W) at different methanol (MeOH) concentrations and the dependence of log PO/M-W on the methanol concentration was compared to the corresponding change in log k' (k' : capacity factor) obtained by reversed-phase liquid chromatography with aqueous methanol. Next, in order to make the chromatographic system approximate more closely to the octanol/water partitioning system, a small quantity of octanol was added to the eluents and also to the octane/aqueous methanol partitioning system and further comparisons were made. It was found that the octanol effect was minimum at 50% MeOH, suggesting that the chromatographic system with eluents containing about 50% MeOH has properties more similar to the octanol/water partitioning system than with eluents of other compositions. This confirms our previous result that the log k' parameter obtained at 50% MeOH yields a better correlation with log Poct (Poct : octanol/water partition coefficient) than those obtained at other mobile phase compositions in the range from 5 to 70% MeOH.
