Irregular retention properties of 21-aminosteroid antioxidants in octylsilane bonded-phase high-performance liquid...

The retention characteristics of two novel 21-aminosteroid antioxidants, 21-[4-(2,6-di-1-pyrrolidinyl-4-pyrimidinyl)-1-piperazinyl]-16 alpha-methylpregna-1,4,9(11)-triene-3,20-dione dimethanesulfonate (I) and 21-[4-(2,5-di-N-diethylamine-2-pyridinyl)-1-piperazinyl]-16 alpha-methylpregna-1,4,9(11)-triene-3,20-dione hydrochloride (II), in octylsilane bonded-phase high-performance liquid chromatography were examined in detail. Both I and II exhibited irregular retention behaviour which could be explained by the dual retention mechanism model proposed by A. Nahum and Cs. Horváth [J. Chromatogr., 203 (1981) 53]. Unless an amine modifier was added to competitively inhibit association with exposed silanol binding sites, the retention of both compounds in a 70% acetonitrile mobile phase was primarily due to silanophilic interactions. Addition of amine modifiers, lowering the pH, and increasing the sodium ion concentration of the mobile phase all decreased retention times, and modifiers capable of hydrogen bonding diminished peak tailing.