[Studies on the retention mechanism of N-methylaniline bonded silica for high performance liquid chromatography]

Three N-methylaniline bonded stationary phases containing different bonding amounts were prepared by modifying silica gel with N-methylanilinetriethoxysilane. Influences of the bonding amounts on the retentions and selectivity of polycyclic aromatic hydrocarbons(PAHs), polar-, acid- and basic-substituted aromatic compounds were investigated in reversed- and normal-phase high performance liquid chromatography. In the reversed-phase liquid chromatography, the plots of logk' against the carbon atom numbers for alkylbenzenes are linear, and the retentions and relative retentions of the solutes(including alkylbenzenes, PAHs and nitrobenzenes) increased with the increase of the bonding amounts and water volume fractions in mobile phase. The results indicated that the hydrophobic interaction played a major role in the retention process. In the normal-phase liquid chromatography, the retentions of PAHs increased and the retentions of nitrobenzenes decreased with the increase of bonding amounts. With the increase of bonding amounts, the retentions of acidic compounds increased and the retentions of basic solutes decreased considerably. It is indicated that the number of imino groups increased and the activity of residual silanols diminished with the increase of bonding amounts. The retentions of solutes on the stationary phases result from acid-basic, dipole-dipole, pi-pi and charge transfer interactions in the normal phase chromatography.