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

The 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 mu m 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 C-13 and Si-29 cross-polarisation-magic-angle spinning and suspended-state H-1 NMR spectroscopy. The NMR spectroscopy results revealed that the alkyl chains of 3 mu m particle size phase are more ordered than those of 5 mu m 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.

Automated summary

This study aimed to enhance molecular-shape selectivity and grafted polymer characteristics by altering particle size, pore size, and polymer chains of polymer-silica hybrid materials. The hybrid materials were prepared with silica of different particle sizes using surface-initiated copolymerizations, characterized by various techniques, and evaluated for chromatographic performance.