Overloading study of bases using polymeric RP-HPLC columns as an aid to rationalization of overloading on silica-ODS phases

The separation of ionized bases by reversed-phase liquid chromatography with alkyl silica columns often leads to severely tailed bands that are highly detrimental. Band shape and its dependence on sample mass are notably different when mobile-phase pH is changed, and this behavior has not been previously explained. Ionized silanols present in the stationary phase have been credited with a role in determining peak shape. In the present study, separations on two different polymer columns were compared with those previously obtained on alkyl silica phases. Because silanols are absent from polymer columns, this comparison enabled us to assess the role of silanols in separations on alkyl silica phases and to offer an explanation of why band shape changes with sample size and mobile-phase pH for both polymer and silica-based phases.