Investigation on the Impact of Using Different Mobile Phase Ratios of Acetonitrile to Methanol on Reversed Phase Phenyl Selectivity

For the greatest π-π interaction with phenyl phases, methanol is the preferred solvent over acetonitrile as the π electrons associated with the nitrile (C≡N) bond in acetonitrile compete for the π-π interaction between the phenyl phase and the analyte. However, because of the higher viscosity of methanol/water mobile phases, the addition of acetonitrile with methanol when using phenyl phases is often recommended to reduce the mobile phase viscosity and thus reduce the backpressure associated with methanol/water mixtures. In this study, we show that the addition of acetonitrile to methanol does not significantly disrupt the π-π interaction of phenyl phases, but does suppress, to some degree, the interaction as a function of the relative amount versus methanol.