Packed‐column capillary electrochromatography and capillary electrochromatography‐mass spectrometry using a lithocholic acid stationary phase

Abstract

The preparation and characterization of a novel lithocholic acid (LCA)-based liquid crystalline (LC) stationary phase (SP) suitable for application in packed-column CEC and CEC coupled to MS is described. The extent of bonding reactions of LCA-SP was assessed using 1 H-NMR, 13 C-NMR and elemental analysis. This characterization is followed by application of the LCA-SP for separation of β-blockers, phenylethylamines (PEAs), polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Using the optimum mobile phase operating conditions (pH 3.0-4.5, 10 mM ammonium acetate, 85% v/v ACN), a comparison of the chromatographic ability of the aminopropyl silica phase vs. the LCA-bonded phase was conducted. The results showed improved selectivity for all test analytes using the latter phase. For example, the CEC-MS of β-blockers demonstrated that the LCA-bonded phase provides separation of six out of seven β-blockers, whereas the amino silica phase provides four peaks of several co-eluting β-blockers. For the CEC-MS analysis of PEAs, the LCA-bonded phase showed improved resolution and different selectivity as compared to the aminopropyl phase. An evaluation of the retention trends for PEAs on both phases suggested that the PEAs were retained based on varying degree of hydroxyl substitution on the aromatic ring. In addition, the MS characterization shows several PEAs fragment in the electrospray either by loss of an alkyl group and/or by loss of H 2 O. Finally, the LCA-bonded phase displayed significantly higher separation selectivity for PAHs and PCBs as compared to the amino silica phase.

Terminal‐vinyl liquid crystal crown ether‐modified, vinyl‐functionalized hybrid silica monolith for capillary electrochromatography

“…As illustrated in Fig. 7, six solutes could be separated within 30 min and the mixture was eluted in the order of increasing hydrophobicity on LCCE‐TMOS‐VTMS column with the same order on the liquid crystal stationary phase 35, while all components were co‐eluted with less retention on TMOS‐VTMS column, which indicated that the structure of liquid crystal crown ether played a key role. Compared with supramolecular calixcrown staionary phase 12, more analytes would be separated on LCCE‐TMOS‐VTMS column.…”