Selectivity enhancement for the separation of shape‐constrained isomers by particle size‐derived molecular ordering and density in reversed‐phase liquid chromatography

Abstract

AbstractThe purpose of this study is to describe the enhancement of molecular‐shape selectivity and grafted polymer characteristics by altering the particle size, pore size, and polymer chains of polymer‐silica hybrid materials used in reversed‐phase liquid chromatography. The poly(octadecyl acrylate‐alt‐N‐octadecylmaleimide)‐grafted silica hybrid materials were prepared with 3 and 5 μm particle size silica, respectively. The alternating copolymerisations were conducted with 3‐mercaptopropyltrimethoxysilane‐modified silica via surface‐initiated radical chain transfer reactions. The polymer‐silica hybrid materials were characterised by elemental analyses, diffuse reflectance FTIR spectroscopy, solid‐state 13C and 29Si cross‐polarisation–magic‐angle spinning and suspended‐state 1H NMR spectroscopy. The NMR spectroscopy results revealed that the alkyl chains of 3 μm particle size phase are more ordered than those of 5 μm particle size phase at lower temperatures and vice versa at higher temperatures. After detailed characterisation, the hybrid materials were packed into a stainless‐steel column, and their chromatographic performance with polycyclic aromatic hydrocarbons was compared. Regardless of the grafting‐density, ordering of the alkyl chains, and column temperature, differences in molecular‐planarity selectivity molecular‐linearity were observed. Aspects of molecular‐shape selectivity were also evaluated using the standard reference material for priority pollutant polycyclic aromatic hydrocarbons.