The type of stationary phase has a significant impact on analyte selectivity in liquid chromatography. One can tune their chromatography to specific solute–stationary phase interactions such as hydrophobic, ionic, hydrogen-bond acidity and basicity, steric resistance, and π-π based on the stationary phase. In sample matrices that contain a diverse set of analytes, poor selectivity leads to decreased separation, lower efficiency, and increased work time. Phenyl stationary phases are often used to separate mixtures of analytes with unsaturated carbon – carbon skeletons with conjugated π-bonds because it is able to form strong π-π interactions compared to traditional C18 or C8 stationary phases. The phenyl stationary phase is a π-basic compound due to the alkyl side chain donating electron density into the ring. The π-basic nature of the phase leads to increased interactions with π-acidic compounds, thus increasing their retention on the column. A phenoxy stationary phase has an oxygen inserted into the alkyl chain which tethers the ring to the stationary phase support. The oxygen enhances the π-basic properties of the ring due to its ability to donate electron density into the ring, thus enhancing π-π interactions with π-acidic compounds which increases selectivity and retention. In the current study, a commercial phenyl and a custom phenoxy phase are compared to determine their relative retentions and selectivities for mono- and di-substituted benzene derivatives.

Comparison of phenyl and phenoxy stationary phase types based on Pi-Pi Interactions on chromatographic retention

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