Additional investigations into the retention mechanism of hydrophilic interaction liquid chromatography by linear solvation energy relationships

• 23 HILIC stationary phases were compared by linear solvation energy relationships.
• PH and buffer change may elevate the H-bond basicity of the HILIC systems.
• Acids seem to be more affected by the hydro-organic environment than bases.
• Intramolecular H-bonding in acids reduces the number of interaction sites.

In analogy to our previous publication, the hydrophilic interaction liquid chromatography mechanism was examined in terms of hydrogen bonding, coulombic interactions and phase ratio using linear solvation energy relationships. At first, 23 commercially available and in-house synthesized chromatographic supports are discussed in order to obtain system constants at pH 5.0 with ammonium acetate as buffer salt. Subsequently we compared these outcomes with our former results obtained at pH 3.0 with ammonium formate as buffer additive. Goodness of fit in terms of the adjusted multiple correlation coefficient was found to be reduced under the new conditions. No universal model which simultaneously comprised acidic, basic and neutral analytes could be performed. A significant enhancement of the HILIC systems hydrogen bond basicity was found when changing the pH and buffer counter ions. Even though packing materials showed similar selectivity profiles during the collection of the experimental retention data, different forces were found to account for the overall retention (e.g. Shiseido PC HILIC and Nucleodur HILIC). This indicates that HILIC type selectivity is rather based on a sum of additive or multiplicative phenomena.