Preparation of two regional isomers self-crosslinked ionic liquid modified silica stationary phase for mixed-mode chromatography and its application for additive detection.

In this study, two self-crosslinked polymeric ionic liquids (SPILs) with varying chain lengths were immobilized onto silica surfaces via thiol-ene click reaction, and the synthesized stationary phases were subsequently applied to mixed-mode chromatographic separations. Comprehensive characterization using Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and elemental analysis (EA) confirmed the successful synthesis of two mixed-mode chromatographic stationary phases. The separation performance was systematically investigated by evaluating diverse analytes in reversed-phase liquid chromatography (RPLC), hydrophilic interaction liquid chromatography (HILIC), and ion exchange chromatography (IEC). The results demonstrated their promising potential for mixed-mode separations, with Sil-C9Im-NTf exhibiting superior separation selectivity. Both columns demonstrated satisfactory retention reproducibility. Under certain conditions, Sil-C3Im-NTf achieved the maximum theoretical plates number of 101,640 plates/m in the separation of m-nitrobenzoic acid. The retention mechanisms were elucidated through thermodynamic analysis and the linear solvation energy relationships (LSER) model, while the effects of mobile phase conditions on chromatographic retention behavior were investigated. Finally, Sil-C9Im-NTf was applied in practical applications for the separation and determination of sulfamethoxazole and sulfamethazine in fresh milk, bromate ions in wheat flour, and iodide ions in powdered milk. These results demonstrate the potential application of the prepared stationary phase in the detection of food additives.