Retention mechanism in reversed-phase liquid chromatography: Specific effects of propiophenyl and multifunctional (cyanopropyl-octadecyl) bonded silicas

Accurate measurements of the retention of homologous series were made on a phenyl-3-propyl-bonded silica and on a multifunctional silica (simultaneously bonded with n-octadecyl and cyanopropyl groups). It is shown that the retention of these types of phases is governed by their hydrocarbonaceous part, as on pure n-alkyl-bonded silicas. Energetic considerations gained from plots of log k' vs. log k' allow one to characterize global effects of an organic modifier on the chromatographic equilibrium. In particular, the influence of pi-pi interactions on retention is shown. These types of curves enable one also to compare different columns in RPLC. In a general way it is shown that the specific effects are superimposed on the effect of hydrocarbonaceous parts, which is always predominant, The mechanism of insertion of the solute is always valid and multifunctional phases are intermediate between pure alkyl-bonded silica and functionalized phases.