Enhancement of molecular shape selectivity by in situ anion-exchange in poly(octadecylimidazolium) silica column.

This paper demonstrates that in situ anion exchange could be successfully applied as a new method for modifying the surface properties of a poly(octadecylimidazolium)-grafted silica stationary phase to tune and enhance selectivity. Specifically, the original stationary phase was prepared by surface-initiated radical chain-transfer polymerization of 1-vinyl-3-octadecylimidazolium bromide as an ionic liquid monomer; the Br(-) counter anion was then exchanged for methyl orange via an in-column process. As evaluated via the separation of constrained isomers of polycyclic aromatic hydrocarbons (PAHs), the in situ exchange enhanced the molecular shape-selectivity performance. Enhanced selectivity was also confirmed using Standard Reference Material (SRM) 869b (column selectivity test mixture) and SRM 1647e (16 priority pollutant PAHs). The reproducibility of new column was tested via the separation of pyrene, triphenylene, benzo[a]anthracene and chrysene with methanol as eluent at 10 °C and the RSD values (n=12) of the retention factors of them are within 0.27-0.77%.