Characterization of Fullerene-Modified Silica as a Complement to Graphite-like phases for Use in Two-Dimensional High Performance Liquid Chromatography

Abstract

Carbonaceous sorbents have a long and rich history of development and application in all areas of separation science. Interest in these materials has been fueled by observations that solute-sorbent interactions are mainly adsorptive in nature and thus selectivities are frequently quite different from what is observed with small organic ligands bonded to porous substrates. However, despite over four decades of intense study and development of these materials for use in reversed-phase liquid chromatography, wide adoption continues to be hindered by a few significant, negative attributes of these materials, most notably irreversible adsorption and poor peak shape and separation efficiency for some classes of compounds. In this work we describe the results of a study aimed at characterization of C60 fullerene-modified silica (FMS) materials that we believe nicely complement existing graphite-like carbonaceous phases for use in liquid chromatography. Since their first synthesis about 20 years ago, FMS materials have received surprisingly little attention, which has been focused mainly on the separation of highly aromatic compounds. Here, we use retention data for well-established sets of both nonionizable and ionizable low molecular weight probe solutes to demonstrate that FMS both exhibits graphite-like characteristics (i.e., selectivity for structural isomers and enhanced retention of polar compounds) and has selectivity characteristics that are largely unique in comparison to over 600 other materials used for reversed-phase liquid chromatography. In addition, FMS exhibits much improved peak shape and separation efficiency for compounds that are known to be problematic when separated by use of graphite-like phases. This combination of attributes makes FMS an excellent complement to graphite-like phases for use in two-dimensional liquid chromatography, where unique selectivity compared to conventional bonded reversed-phase materials, along with good peak shape and separation efficiency are of paramount importance for successful two-dimensional liquid chromatographic separations.