Phosphatidic acid-functionalized monolithic stationary phase for reversed-phase/cation-exchange mixed mode chromatography

A novel phosphatidic acid functionalized polymeric monolithic column was prepared through the thermally initiated co-polymerization of 12-methacryloyl dodecylphosphatidic acid (MDPA) and ethylene glycol dimethacrylate (EDMA) in the presence of 1,4-butanediol and isopropanol as porogens within 100 mm I.D. capillaries. The polymerization conditions of monolithic columns were systematically optimized in order to obtain good permeability, stability and column efficiency. The reproducibility of the optimized monolithic column was also satisfactory. The physicochemical properties of the monolithic column were evaluated by use of instrumental techniques including scanning electron microscopy, Fourier transform infrared spectra, zeta-potential analysis and micro-HPLC. A series of test compounds such as small peptides, alkylphenones, etc., were employed to investigate the retention mechanism on the poly(MDPA-co-EDMA) monolithic column. The results demonstrate that both hydrophobic and cation-exchange interactions could contribute to the overall retention of analytes. Furthermore, the novel reversed-phase/cation-exchange mixed mode monolithic column was applied to the separations of small peptides, phenols, water-soluble vitamins B, and pharmaceutical compounds. The successful applications indicate the potential of the poly(MDPA-co-EDMA) monolithic column in complex sample analysis.