Ionic Liquids Functionalized Graphene Quantum Dots-Bonded Silica as Multi-Mode HPLC Stationary Phase with Enhanced Selectivity for Acid compounds

Qi Wu, Yaming Sun, Jie Gao, Lixiao Chen, Shuqing Dong, Guoying Luo, Hui Li, Litao Wang, Liang Zhao

Index: 10.1039/C7NJ05200F

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Abstract

Graphene quantum dots (GQDs) which can form hydrophobic, π-π stacking, hydrogen bond and hydrophilic interaction with analytes, is a kind of multifunctional separation material. GQDs-based stationary phases have great prospect in HPLC. In this work, 1-aminoethyl-3-methylimidazolium bromide ionic liquids (ILs) were chosen as functional molecules to improve the chromatographic performance of GQDs-bonded silica stationary phase. This new phase could be applied in multiple separation modes including normal phase, reversed phase, ionic exchange and hydrophilic chromatography modes. Anilines, phenols and polycyclic aromatic hydrocarbons were efficiently separated on this ILs/GQDs/SiO2 column within 10 minutes in normal phase and reversed phase modes. Five inorganic anions were baseline separated in ionic exchange mode. Hydrophilic compounds including alkaloids, glycosides, amino acids and aromatic acids achieved satisfactory resolution on this stationary phase in hydrophilic chromatography mode. The separation performance of ILs/GQDs/SiO2 column was compared to that of GQDs/SiO2 column and ILs/SiO2 column, it was found that ILs/GQDs/SiO2 column showed better separation performance than the other two, which indicated ILs and GQDs had certain synergistic and complementary effects. Introduce of ILs enhanced the separation performance of GQDs-based phase especially for acid compounds. Through investigating the effects of buffer pH, buffer concentration and water content in mobile phase, it was found electrostatic adsorption retention mechanism played a main role in hydrophilic chromatography mode. This stationary phase which allows to choose appropriate separation modes on the basis of analytes, possesses practical prospect after further improvement.