Characterization of adsorbents by high-performance liquid chromatography using aromatic hydrocarbons Porous graphite and its comparison with silica gel, alumina, octadecylsilica and phenylsilica

Abstract

The retention characteristics of 52 aromatic hydrocarbons, mostly alkylbenzenes, were measured on porous graphite using methanol as the mobile phase. There is a linear dependence of log k′ on the number of carbon atoms, (i) for polymethylbenzenes whose methyl groups are all in ortho positions and (ii) for n-alkylbenzenes above butylbenzene. As with alumina and silica gel, the ortho effect for graphite was also observed, but graphite shows much higher α values (the increase in log k′ for addition of a carbon atom) than any of the other packing materials studied. The superior selectivity of graphite is in line with its crystalline structure, consisting of a flat, crystalline array of hexagonally arranged carbon atoms. In terms of optimum eluent and retention graphite behaves like a reversed-phase material, but in terms of selectivity towards isomeric compounds it behaves like the oxide adsorbents silica gel and alumina.