Zeitschrift für Chromatographieforschung

A Comparison of Silica C and Silica Gel in Hydrophilic Interaction Mode: The Effect of Stationary Phase Surface Area

Eman Santali

Hydrophilic interaction chromatography (HILIC) was first described in 1990 although several interesting reviews focusing on general aspects of HILIC have been published [2-4] and it is becoming increasingly popular, (HILIC) is far from being completely understood.

To assess the effect of silica gel structure on retention in HILIC, a test system was developed using the quaternary ammonium ions benzyltrimethylammonium (BTM), benzyltriethylammonium (BTE) and benzyldimethylhexylammonium (BDM) as probes with tetramethylammonium acetate (TMA) as the counter-ion competing against the interaction of the test probes with ionised silanols in the stationary phases. Five columns were examined: 300 Å and 100 Å ACE silica gel columns, 100 Å and 60 Å Kromasil silica gel columns and a Cogent Silica- C column. Retention time was obtained for the test probes at different acetonitrile concentrations with all the mobile phase mixtures containing 10 mm tetramethylammonium acetate (TMAA) buffer at pH [6.00]. In all cases BTE, which has the intermediate ionic radius, was the most retained probe at 20% acetonitrile suggesting that retention on silica gel at low % acetonitrile was due to a balance between lipophilic interaction with siloxane groups and ion exchange. All phases gave “U” shaped plots for log k against percentage of acetonitrile with the steepest rise in retention occurring between 80 and 90% acetonitrile. BTM was the most retained probe at 90% acetonitrile and was most retained on the 60 Å Kromasil column and least retained on the 300 Å ACE silica gel columns.