Evaluation of a series of phenyl-type stationary phases in supercritical fluid chromatography with the linear solvation energy relationship model and its application to the separation of phenolic compounds.

In recent years, supercritical fluid chromatography (SFC) has become a powerful tool in modern analytical chemistry, and the diversity of stationary phases in SFC promotes phenyl-type phases to confront with a significant resurgence of interest. In this paper, a series of phenyl-type stationary phases with different substituted benzenes involving N-propylbenzamide (PB), 4-fluoro-N-propylbenzamide (PB-F), and 4-ethyl-N-propylbenzamide (PB-ET) were synthesized. Retention mechanism of these phases in SFC was investigated using a linear solvation energy relationship (LSER) model. The phenyl-type stationary phases with all positive parameters can provide all types of interaction, typically involving hydrogen bonding, dipole-dipole and dispersive interactions. The different benzene's substituents of the stationary phases mainly affected their hydrogen bonding and dipole-dipole interactions, which could be reflected by the angle between the solvation vectors to some extent. The k-k plot showed that the selectivity difference of phenyl-type stationary phases was closely related to the type of solute. Thus, based on twenty-five natural phenolic compounds, two systems with high orthogonality (63.49%) were constructed using three columns, namely phenyl column (PHE) × PB-F and PB × PB-F. Finally, after investigating the influence of chromatographic conditions, ten flavonoids could be separated by using PB, PB-F and PHE columns in SFC.