Application of reversed-phase ion-pair chromatography for universal estimation of octanol-water partition coefficients of acid, basic and amphoteric drugs

This paper is to establish a reversed-phase ion-pair chromatography (RP-IPC) method for universal estimation of the octanol/water partition coefficients (log P) of a wide range of structurally diverse compounds including acidic, basic, neutral and amphoteric species.  The retention factors corresponding to 100% water  (log k_w) were derived from the linear part of the log k′/ф relationship, using at least four isocratic log k′ values containing different organic compositions.  The log k_w parameters obtained were close to the corresponding log P values obtained with the standard “shake flask” methods.  The mean deviation for test drugs is 0.31.  RP-IPC with trifluoroacetic acid as non classic ion-pair agents can be applicable to determine the log P values for a variety of drug-like molecules with increased accuracy.