Retention behavior of small polar compounds on polar stationary phases in hydrophilic interaction chromatography

Retention characteristics of four polar stationary phases (i.e., amide, amino, silica and sulfobetaine) were studied by using a group of small polar compounds in hydrophilic interaction chromatography (HILIC). Different polar stationary phases shared certain degrees of similarity, but also exhibited differences in retentivity and selectivity for the model compounds. Among the four columns studied, HILIC Silica column had the least retention for the model compounds, but also showed different selectivity from other three columns. Experimental data also provided some evidences that functional groups on the stationary phases might have certain degrees of influence on selectivity possibly through secondary interactions with the model compounds. The retention of the acids on the amino phase decreased with increasing salt concentration in the mobile phase due to the ion-exchange effect, and the retention process was endothermic as opposed to exothermic on other phases. This study also systematically investigated the effect of various experimental factors on the retention of the polar stationary phases, such as acetonitrile content, column temperature, buffer pH, salt type and concentration in the mobile phase.