The potential uses of bonded liquid crystal materials in high-performance liquid chromatography and supercritical-fluid chromatography

Abstract

For almost 30 years highly ordered stationary phases made from liquid crystals have successfully separated structural isomers. This type of stationary phase has been employed in gas chromatography (GC) where the liquid crystal could be physically coated on the solid phase and retain long column life, instead of high-performance liquid chromatography (HPLC) where chemical bonding is required. Two methods to bond liquid crystal materials to silica have recently been used succesfully. Initially a standard organosilane reagent was used, but another method that directly bonds liquid crystal containing terminal olefins to hydride silica surfaces has been developed in which the Si C bond remains stable over a broad range of HPLC conditions. Characterizations by diffuse reflectance infrared Fourier transform spectroscopy and carbon-13 cross polarization magic angle spinning nuclear magnetic resonance spectroscopy indicate some degree of order remains in the liquid crystal molecules even after they are bound to the surface. Chromatographic studies indicate that the phase has a “slolt-like” configuration on the surface which leads to separation of molecules based on such molecular properties as length/breadth ratios and planitary. The use of liquid crystal stationary phases in HPLC cuold be useful in the separation of polyaromatic hyrocarbons (PAHs), chiral compounds, and biological materials, such as steroid isomers.