Researchers of the Kumamoto University and the Lanzhou Institute of Chemical Physics of the CAS have proposed a new strategy for the design of a new chromatographic stationary phase via simple modifications of the counter anions in poly(ionic liquid)-grafted silica phase based on ionic self assembly technology. The phase with methyl orangedye as counter anions exhibits ultra-high selectivity towards shape-constrained isomers.

They have demonstrated that poly(ionic liquid)(PIL)-grafted silica could be easily obtained by surface radical-chain transfer polymerization, and furthermore, counter anions could be simply modified by ionic self-assembly to tune the property of the phase; the phase with dye as counter anions exhibits ultra-high shape selectivity for polycyclic aromatic hydrocarbons (PAHs). However, buffer solvents could not be used as the eluent because the stationary phase was combined by anions and cations through ionic interactions. Nevertheless, such stationary phases still have sufficiently attractive advantages in the separation of hydrophobic shape constrained isomers. The enhanced selectivity may be a result of the highly ordered arrangement between the C18 chain and rigid azobenzene in Sil–PImC18–MO due to the molecular interactions. Multiple interactions including hydrophobic effect and aromatic interaction between the PAHs and the functionalized groups (azobenzene and imidazolium) in the stationary phase were observed.

The work has offered a new possibility for the design of complex functional materials for applications in chromatography and electrochemistry conducted using the ionic self-assembly (ISA), which are not otherwise easy to synthesize by traditional chemical approaches.

The findings have been published in Chem. Commun (Chem. Commun., 2010, 46, 8740–8742).