Imidazolium ionic liquid-enhanced poly(quinine)-modified silica as a new multi-mode chromatographic stationary phase for separation of achiral and chiral compounds.

In this work, a novel imidazolium ionic liquid-functionalized poly(quinine)-modified silica stationary phase (Sil-PQn-MIm) was successfully synthesized via surface radical chain transfer and nucleophilic substitution reaction. The modified silica was confirmed by series of characterizations including Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The multi-mode chromatographic performances of the Sil-PQn-MIm column were investigated by anion-exchange mode for separation of aromatic acid samples, hydrophilic interaction mode for separation of nucleosides/nucleobases and sulfanilamides, and reversed-phase mode for separation of alkylbenzenes, benzene and polycyclic aromatic hydrocarbons (PAHs), and the Tanaka test mixtures, respectively. As expected, compared to the Sil-PQn column only with quinine as functional group, the Sil-PQn-MIm column further modified by imidazolium ionic liquid possessed higher separation performance, especially for the separation of nucleosides/nucleobases. The effects including buffer concentration, pH, organic solvent content and column temperature on chromatographic performance were studied, which proved that multiple interactions including electrostatic, hydrophobic and hydrophilic interactions can be simultaneously existed between the stationary phase and the analytes. In addition, reproducibility and efficiency of the Sil-PQn-MIm column were also investigated, the results illustrated that the stationary phase have good enough reproducibility (RSDs 0.15%-0.72%, n = 7) and high efficiency (plates per meter, ~90000 plates/m). In conclusion, the prepared stationary phase with multiple-mode retention capabilities could realize separation for various types of samples by optimizing chromatographic conditions, even for some chiral compounds.