Temperature dependence of retention in reversed-phase liquid chromatography. 2. Mobile-phase considerations

The retention mechanism in reversed-phase liquid chromatography (RPLC) has been examined over a wide temperature range with emphasis on the role of the mobile phase. van't Hoff plot shapes were used to assess the retention mechanism, and the data showed evidence of the hydrophobic effect when water-rich and/or hydrogen-bonded mobile phases such as methanol/water were used. However, different van't Hoff plot shape was observed with acetonitrile/water mobile phases, indicating a change in the retention mechanism. These data showed that the hydrophobic effect, which had previously been proposed as the driving force for retention, is not a satisfactory explanation for the retention process in all RPLC systems.