Molecular Shape Selectivity for Polycyclic Aromatic Compoundson a Poly(4-vinylpyridine) Stationary Phase in Liquid Chromatography

Abstract

Poly(4-vinylpyridine) (P4VP) was introduced as a stationary phase in liquid chromatography (LC) and the retention behavior of polycyclic aromatic compounds (PACs) on the P4VP phase has been investigated by comparing with that observed on commercially-available octadecylsilica (ODS) and phenylbutylsilica (PBS) phases. On the P4VP phase, a good linear relationship between the logarithmic retention factor and the molecular size of planar PACs was obtained, however, a unique selectivity for some planar PACs was also observed. The P4VP phase demonstrated a specific retention trend, where planar PACs having "square-like" molecular shape were strongly retained. The above trend clearly suggested a unique selectivity of the P4VP phase for PACs. In addition, compared to the typical ODS and PBS phases, the P4VP phase showed a good molecular shape recognition capability for planar/non-planar PACs with a similar two-dimensional molecular size. The P4VP phase showed a very small retention for various alkylbenzenes, suggesting somewhat limited contribution of the hydrophobicity of the analytes to the retention. In the investigation for the selectivity to structural isomers, the P4VP phase exhibited a unique selectivity for isomers of dichlorobenzene and dibromobenzene when compared to the typical ODS and PBS phases. The trend can be interpreted as a dipole-dipole interaction between pyridyl groups in the P4VP ligands and the analyte.