Ionic liquid and octadecylamine co-derived carbon dots for multi-mode high performance liquid chromatography

• Novel carbon dots with applicability in multi-mode chromatography. • A simple method to control the hydrophobicity/hydrophilicity of carbon dots. • Good separation performance for various kinds of compounds. • Retention mechanism explanation by linear solvation energy relationship. In this work, a novel kind of carbon dots (CDs) are synthesized by citric acid, 1-aminoethyl-3-methylimidazolium bromide ionic liquid and octadecylamine. Due to the variety of precursors, the synthesized CDs possess multiple functional groups including carboxyl, amino, hydroxyl and imidazole groups. One CDs functionalized silica gels (Si-CDs) chromatographic column can be applied in three separation modes including reversed-phase liquid chromatography, hydrophilic interaction liquid chromatography and ion exchange chromatography, suitable for separating compounds with different properties. Polycyclic aromatic hydrocarbons, alkylbenzenes, alkaloids, pesticides, antibiotics, sulfonamides, glycosides, inorganic anions, aromatic acids, nucleosides and bases as test compounds can be separated well on this Si-CDs column. For four adjacent analytes of triadimefon, tebuconazole, diniconazole and diclofop, the resolution reaches 3.77, 2.34 and 5.17 with an average column efficiency of 9500 plates/m. Retention mechanism contains hydrophobic, π-π stacking and electrostatic interactions according to linear solvation energy relationship. This Si-CDs column is used for real sample analysis of residual thiamphenicol and chloramphenicol in milk. With simplified sample pretreatment process, spiked recoveries between 89.3%-112% indicates the developed detection method based on this Si-CDs column is not only rapid but also reliable. Using CDs with multiple functional ligands as modifiers for multi-mode stationary phases avoids multi-step modification process of various small molecules on silica gels, which is helpful to the evolution of multi-mode chromatography and nanomaterials-based separation science.