Chemically l-Phenylalaninamide-Modified Monolithic Silica Column Prepared by a Sol−Gel Process for Enantioseparation of Dansyl Amino Acids by Ligand Exchange-Capillary Electrochromatography

Abstract

A new type of chiral monolithic column was successfully developed for the enantioseparation of dansyl amino acids by ligand exchange-capillary electrochromatography (LE-CEC) in this work. The monolithic column matrix was prepared by a sol-gel process and then chemically modified with the spacer (3-glycidoxypropyl)trimethoxysilane and the chiral selector L-phenylalaninamide. After being conditioned with Cu(II) aqueous solution, the ligand exchange-chiral stationary phase (LE-CSP) possesses positive charges. When the external electric field was applied in CEC, electroosmotic flow (EOF) was generated on the surface of LE-CSP in the direction from the cathode to the anode. The EOF was found to be dependent on the applied electric field strength and the composition of the mobile phase. With the increase of pH of the mobile phase, the EOF showed a tendency to decrease. Scanning electron microscopy showed that the chiral monolithic column has a continuous skeleton and large through-pore structure. The separation efficiency (theoretic plate numbers) for the separation of Dns-DL-Leu reached up to 9.0 x 10(4) plates m(-1) for the D-enantiomer and 6.6 x 10(4) plates m(-1) for the L-enantiomer, by using pH 5.5, acetonitrile/0.50 mM Cu(Ac)2-50 mM NH4Ac (7:3) as mobile phase. The reproducibility and lifetime were satisfactory. CEC was carried out with conventional capillary electrophoresis equipment without pressurizing the ends of the capillary. No bubble was formed during the operation, after degassing the mobile phase and conditioning the column.

Preparation of monolithic silica column with strong cation‐exchange stationary phase for capillary electrochromatography

“…Furthermore, chiral stationary phases benefiting from the favorable hydrodynamic properties of silica monoliths have also been reported. Chen et al [13,14] developed ligand exchange chiral stationary phases based on monolithic silica for electrochromatographic separations of dansyl amino acid enantiomers. Modification of chiral selectors, such as polysaccharide, quinine, and proteins bonded onto monolithic silica has been investigated [15 -17].…”

Enantioseparation of Dansylated Amino Acids by Ligand-exchange Capillary Electrophoresis Using L-phenylalaninamide, L-lysine or L-threonine as Chiral Selector

“…L-phenyalaninamide was already used for the resolution of Dns-AAs by Chen 34 with Cu(II) and by Qi 28 with Zn(II) as central metal ion. For the following experiments a similar background electrolyte was chosen to guarantee adequate current.…”

Dynamically coated silica monolith with ionic liquids for capillary electrochromatography

“…However, as the potential applications of unmodified silica monoliths are generally limited, it is necessary to introduce chromatographic functionality onto the silica matrix to exert selectivities. Thus far, two methods, namely post-modification and hybrid organic-inorganic functionalization, are the most commonly used ones [9][10][11][12][13][14]; nevertheless, they need additional surface modification steps or reoptimization for each sol-gel precursor [15]. A much simpler and more convenient method, called dynamic coating, has also captured researcher's attentions, in which a running buffer containing the coating agent is used [16].…”