Tetra-proline-modified calix[4]arene-bonded silica stationary phase for simultaneous reversed-phase/hydrophilic interaction mixed-mode chromatography

A new water-soluble tetra-proline-modified calix[4]arene-bonded silica stationary phase was prepared straightforwardly by an indirect method and characterized by elemental analysis, energy dispersive Spectrometry, solid-state C-13 NMR spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Due to the simultaneous introduction of polar tetra-proline and nonpolar calix[4]arene, the developed column possessing a double retention mode of reverse-phase liquid chromatography and hydrophilic interaction liquid chromatography. A series of hydrophobic and hydrophilic test samples, including nucleosides and nucleotides, amines, monosubstituted benzenes, chiral compounds, and phenols, were used to evaluate the developed stationary phase. A rapid separation capability, high separation efficiency, and selectivity were achieved based on the multiple interactions between solutes and tetra-proline-modified calix[4]arene-bonded silica stationary phase. Moreover, the developed stationary phase was further used to detect and separate hexamethylenetetramine in rice flour. All the results indicated the potential merits of the developed stationary phase for simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.