Determination of hydrophobicity of organic bases on poly(butadiene)-coated alumina and on octadecylsilica columns

Summary The performance of two chromatographic (HPLC) methods recommended for hydrophobicity evaluation of structurally diverse (noncongeneric) solutes was compared. Azole derivative drugs possessing properties of weak organic bases were used as the test solutes. One of the methods, recommended by Minick and co-workers, consists on suppressing specific interactions with the stationary phase (ODS) by adding modifiers to the eluent of neutral pH. The other method, developed previously in our laboratory, yields retention data for nonionized bases due to using poly(butadiene)-coated alumina (PBCA) columns which can be operated under alkaline conditions. It has been demonstrated that in the case of basic solutes, hydrophobicity parameters obtained by the method employing PBCA columns are more reliable. The noncontrolled specific interactions of organic bases with the ODS phase at pH 7.0 remain effective in spite of special precautions undertaken.