Octadecylimidazolium ionic liquids-functionalized carbon dots and their precursor co-immobilized silica as hydrophobic chromatographic stationary phase with enhanced shape selectivity

In this work, 1-vinyl-3-octadecylimidazolium bromide ionic liquids ([C18VIm]Br) and their derived carbon dots (ImC18CDs) were prepared, [C18VIm]Br and ImC18CDs were grafted on the silica to obtain Sil-ImC18 and Sil-ImC18CDs, respectively, and they were also co-grafted on silica which named Sil-ImC18/CDs. Compared with Sil-ImC18 and Sil-ImC18CDs columns, Sil-ImC18/CDs column exhibited enhanced selectivity for separation of tetracyclic/tricyclic polycyclic aromatic hydrocarbon (PAH) isomers, and butylbenzene isomers in reversed-phase liquid chromatography, which may be due to the synergistic effect between ImC18CDs and [C18VIm]Br, the π-π interaction between imidazolium and analytes, etc. Meanwhile, the retention behavior of Sil-ImC18/CDs was further evaluated and compared with the commercial C18 column using different classes of analytes, including standard test mixtures of Tanaka, Engelhardt, SRM869b, SRM870. The results demonstrated that co-grafted column exhibited superior separation performance. And this column was applied to determine the contents of calycosin-7-glucoside, ononin, calycosin and formononetin in the extract of Radix Astragali, which were found that the concentration was 0.25 mg mL−1, 0.15 mg mL−1, 0.13 mg mL−1 and 0.30 mg mL−1, respectively.