HILIC and Mixed-Mode are terms originally used to describe a specific chemical interaction or set of interactions in liquid chromatography. Recently, however, these terms have been more frequently used to describe LC columns offering retention mechanisms that vary, or are orthogonal, to a C18. These columns generally consist of a bonded phase which contains a chemical moiety other than, or in addition to, alkyl carbon chains. By incorporating double bonds, oxygen, nitrogen, or other heteroatoms, alternate retention and selectivity can be accomplished. These chemical interactions are generally not well understood or easily demonstrated, which can leave users frustrated and not using the phase to its potential.

In this study we set out to explore the retention mechanisms of the Restek IBD stationary phase. This proprietary phase offers unique selectivity by embedding a polar group into an alkyl chain which takes a positive charge under selected conditions. In addition to the traditional reversed-phase dispersive interactions, this phase may exhibit hydrogen bonding and anion-exchange interactions which aid in selectivity of specific analytes. Our focus in this presentation is on specific method parameters including temperature, and mobile phase acid strength and concentration and how these changes affect the selectivity of target analytes. By demonstrating the influence of specific method changes on this phase we aim to gather a better understanding of the interactions demonstrated by the IBD phase and its use as a HILIC or mixed-mode phase.