Development of an L-lysine-derived stationary phase for both RP and HILIC separations of complex samples—proof-of-concept in both dimensions of LCxLC

An L-lysine-derived stationary phase comprising a 2C18 alkyl chain with embedded polar groups, including two urea and one amide functionalities (Sil-Lys-2C18), was synthesized for the application in 1D- and 2D-LC for the first time. The same stationary phase was packed into 150 × 2.1 mm and 30 × 3 mm for the first and second dimensions, respectively, and named the short column Sil-Lys-2C18-S. The material was characterized with total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), elemental analysis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and solid-state 13C cross-polarization magic angle spinning (CP/MAS) NMR spectroscopy. Initially, the chromatographic performance was evaluated under reversed-phase liquid chromatography (RPLC) conditions by the Tanaka and Neue test probes. Moreover, the Tanaka test protocol for hydrophilic interaction chromatography (HILIC) was used to observe the performance of the separation of polar analytes. Based on the chromatographic performance evaluation, the 150 × 2.1 mm column was employed to analyze the extracts of chili peppers (Capsicum spp.) containing capsaicinoids, vitamin E, and vitamin C. Outstanding separation of β-, ɣ-, and α-tocopherol isomers was achieved, alongside the separation of terphenyl and triphenylene isomers based on shape selectivity. Moreover, ascorbic acid was also separated on the same column. Therefore, the material was reapplied in both dimensions of comprehensive two-dimensional liquid chromatography (LC×LC) approach, achieving successful orthogonal separation of bioactive compounds in the complex liquor sample compared with commercial columns.

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