The hydrophilicity vs. ion interaction selectivity plot revisited: The effect of mobile phase pH and buffer concentration on hydrophilic interaction liquid chromatography selectivity behavior

• HILIC selectivity investigated at different pH and buffer concentrations.
• Hydrophilicity vs. ion interaction selectivity plots for 18 columns.
• Selectivity changes dominated by silanol activity.
• Hydrophilic selectivity generally unaffected by mobile phase change.

This work systematically investigates the selectivity changes on many HILIC phases from wwpH 3.7–6.8, at 5 and 25 mM buffer concentrations. Hydrophilicity (kcytosine/kuracil) vs. ion interaction (kBTMA/kuracil) selectivity plots developed by Ibrahim et al. (J. Chromatogr. A 1260 (2012) 126–131) are used to investigate the effect of mobile phase changes on the selectivity of 18 HILIC columns from various classes. “Selectivity change plots” focus on the change in hydrophilicity and ion interaction that the columns exhibit upon changing mobile phase conditions. In general, the selectivity behavior of most HILIC columns is dominated by silanol activity. Minimal changes in selectivity are observed upon changing pH between wwpH 5 and 6.8. However, a reduction in ionic interaction is observed when the buffer concentration is increased at wwpH ≥ 5.0 due to ionic shielding. Reduction of the wwpH to < 5.0 results in decreasing cation exchange activity due to silanol protonation. Under all eluent conditions, the majority of phases show little change in their hydrophilicity.