Variation in thickness of a layered silicate on spherical silica particles affected HPLC chiral chromatographic resolution

Abstract The proposed study aims to prepare clay-coated spherical silica particles to be applied as a column packing material for chiral high performance liquid chromatography (HPLC). These particles were prepared by directly growing a hectorite-like layered silicate on porous and non-porous amorphous silica. The direct crystallization of the layered silicate was performed using the reactions of lithium fluoride, magnesium chloride, and silica in the presence of urea under hydrothermal conditions (373 K for 2 d) and led to a homogeneous coverage on the silica surfaces within a 0.4 μm thickness of the aggregates. The resulting layered silicate involved full ion-exchange reactions with an enantiomeric Δ-tris(1,10-phenanthroline)ruthenium(II). The organically modified particles packed into a stainless steel tube optically resolved a racemic mixture of tris(acetylacetonato)ruthenium(II) in a flow of methanol. The resolution efficiency determined by the retention time and full width at half maximum was influenced by the crystalline size and could be adjusted using different porosities of the initial silica and by varying the quantities of added Li and Mg ions to the starting mixtures. Fine platy crystals and their thin layer aggregates on the porous silica contributed toward the good resolution efficiency and a reduction in the elution volume owing to the rapid diffusion of the racemic mixture into the layered silicate.