RETENTION MECHANISMS OF POLYCYCLIC AROMATIC NITROGEN HETEROCYCLICS ONBONDED AMINO PHASES IN NORMAL-PHASE LIQUID-CHROMATOGRAPHY

Two aminoalkyl bonded phases, aminopropylsilica and dimenthylaminoprop ylsilica, operated in the normal-phase mode were investigated regardin g the retention mechanisms of polycyclic aromatic nitrogen heterocycli cs (PANHs). By blocking active interaction sites with methyl substitue nts, the retention mechanisms could be ascertained. The bonded functio nal groups of the aminoalkyl stationary phases were found to be the pr imary adsorption sites. Hydrogen bonding was found to be the dominant retention mechanism for carbazole-type PANHs on both stationary phases and for acridine-type PANHs on the aminopropyl phase. For acridine-ty pe PANHs on dimethylaminopropylsilica, retention was found to be mainl y due to electron donor-acceptor interaction. Residual silanols on the stationary phase support material on these non-end-capped bonded phas es were found to contribute only slightly to the retention of both acr idine- and carbazole-type PANHs. A strong dependence of retention on s teric hindrance of the n-electrons on the nitrogen of acridine-type so lutes was shown. Further, the necessity to consider not only the polar ity and solvent strength but also the selectivity of the mobile phase is demonstrated.