Thermally-treated clay as a stationary phase in liquid chromatography

Spray-dried, spherical synthetic hectorite particles have been thermally-treated at 500 °C for 16 h and used as adsorbent materials in reversed-phase liquid chromatography. The retention of a 22 mono and disubstituted aromatic compounds was evaluated to study the retention mechanisms on the clay mineral. The retention of solutes on the thermally-treated clays was markedly different than that measured on octadecylsilica (ODS) columns under identical conditions, but remarkably similar to retention characteristics of the same solutes on porous graphitic carbon columns. The clay columns exhibit an enhanced selectivity over the ODS column in separation of nitroaromatic positional isomers. Under identical mobile phase compositions, a selectivity, α, of 7.15 between ortho- and para-dinitrobenzene isomers was measured on the clay column compared to a α of 1.04 on the ODS column.