•Two ionic liquid-modified stationary phases with octadecyl chains are prepared.•The stationary phases differ from each other in distribution patterns of the polar groups.•Study of stationary phases via a linear solvation energy relationship mode.•Hydrophobic and aromatic selectivities of these phases are investigated.•Insertion of polar imidazolium moieties into octadecyl groups remarkably impacts the chromatographic behavior.Two new stationary phases modified by alkylimidazoliums were prepared for the first time and characterized. One of the new phases was obtained via monomeric immobilization of octadecylimidazole to γ-chloropropyltrimethoxysilane modified silica to form polar-embedded phase; the other one was prepared by co-immobilization of two silane coupling agents (γ-chloropropyltrichlorosilane and octadecyltrichlorosilane) to silica, followed by quaternization of methylimidazole to form polar-spaced phase. This study was intended to compare the retention characteristics of these two stationary phases using linear solvation energy relationships model, as well as to examine the difference in selectivity by eluting alkylbenzenes, alkylnaphthalenes, condensed-ring and phenylene polynuclear aromatic hydrocarbons on both phases. Different effects of distributions of polar functional group and octadecyl chain were found to impact the chromatographic properties.Novel octadecyl stationary phases differ in distribution of imidazolium group have been prepared for the first time and comparatively evaluated via linear solvation energy relationships (LSER) model.

•Two ionic liquid-modified stationary phases with octadecyl chains are prepared.•The stationary phases differ from each other in distribution patterns of the polar groups.•Study of stationary phases via a linear solvation energy relationship mode.•Hydrophobic and aromatic selectivities of these phases are investigated.•Insertion of polar imidazolium moieties into octadecyl groups remarkably impacts the chromatographic behavior.Two new stationary phases modified by alkylimidazoliums were prepared for the first time and characterized. One of the new phases was obtained via monomeric immobilization of octadecylimidazole to γ-chloropropyltrimethoxysilane modified silica to form polar-embedded phase; the other one was prepared by co-immobilization of two silane coupling agents (γ-chloropropyltrichlorosilane and octadecyltrichlorosilane) to silica, followed by quaternization of methylimidazole to form polar-spaced phase. This study was intended to compare the retention characteristics of these two stationary phases using linear solvation energy relationships model, as well as to examine the difference in selectivity by eluting alkylbenzenes, alkylnaphthalenes, condensed-ring and phenylene polynuclear aromatic hydrocarbons on both phases. Different effects of distributions of polar functional group and octadecyl chain were found to impact the chromatographic properties.Novel octadecyl stationary phases differ in distribution of imidazolium group have been prepared for the first time and comparatively evaluated via linear solvation energy relationships (LSER) model.