Separation behavior of amino acid enantiomers in ligand exchange micellar electrokinetic chromatography

Chen, Zilin; Lin, Jin‐Ming; Uchiyama, Katsumi; Hobo, Toshiyuki

doi:10.1002/(sici)1520-667x(1999)11:7<534::aid-mcs5>3.3.co;2-1

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“…19 It has widely been used in the chromatographic separations in the modes of ligand exchangeliquid chromatography (LE-LC), 19,20 ligand exchange-capillary electrophoresis (LE-CE), [21][22][23] and ligand exchange-micellar electrokinetic chromatography (LE-MEKC). [24][25][26][27][28] Advances in chiral separations based on ligand exchange were reviewed in our recent paper. 29 Although ligand exchange has been used in chiral separations for 30 years, no paper using ligand exchange in CEC, except for the recent report, 17 was published.…”

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“…Ligand exchange, introduced in liquid chromatography by Davankov and Rogozhin in the 1970s, is based on a chiral discrimination principle with high enantioselectivity for the chiral resolution of chelate complex-forming compounds such as amino acids, hydroxy acids, and peptides . It has widely been used in the chromatographic separations in the modes of ligand exchange-liquid chromatography (LE-LC), , ligand exchange-capillary electrophoresis (LE-CE), − and ligand exchange-micellar electrokinetic chromatography (LE-MEKC). − Advances in chiral separations based on ligand exchange were reviewed in our recent paper . Although ligand exchange has been used in chiral separations for 30 years, no paper using ligand exchange in CEC, except for the recent report, was published.…”

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

2001

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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.

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

2001

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“…Micellar electrokinetic chromatography (MEKC), introduced by Terabe [12] in 1984, is a useful technique for the CE analysis of uncharged compounds. Chen and Lin [13][14][15][16] published on the simultaneous separation of positional and optical isomers of fluoro-DL-phenylalanine, tyrosine as well as tryptophan derivatives, and a mixture of underivated and dansylated amino acids using LE-MEKC. Interestingly, the addition of the achiral surfactant SDS not only significantly improved the resolution but led to the reversal of the enantiomer migration order (EMO) for phenylalanine and tryptophan enantiomers.…”

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Chiral separation based on ligand‐exchange capillary electrophoresis using a copper(II)‐L‐ornithine ternary complex as selector

2005

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Chiral separation based on ligand-exchange capillary electrophoresis using a copper(II)-L-ornithine ternary complex as selectorA ligand-exchange capillary electrophoresis was explored, with L-ornithine as the ligand and copper(II) as the central ion. Its applicability was demonstrated with underivatized and dansyl amino acids, a dipeptide, and drugs with amino alcohol structure. The enantioselectivity was found to be strongly dependent on pH and copper(II)-L-Orn complex concentration. Due to the adsorption of the positively charged species onto the capillary inner walls, the chiral separation selectivity is very high while the efficiency is relatively low. Permanent 1,3-propanediamine-coated capillaries show an improved separation efficiency and theoretical plate numbers increasing from 10 4 to 10 5 . Similar phenomena were observed when sodium dodecyl sulfate (SDS) micelles were added to the copper(II) complex solution. The poor separation efficiency of chiral compounds in uncoated capillaries may result from the low rate of the ligand-exchange reactions, and the high enantioselectivity may derive from the complexing process in the adsorbed phase.

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Separation behavior of amino acid enantiomers in ligand exchange micellar electrokinetic chromatography

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

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

Chiral separation based on ligand‐exchange capillary electrophoresis using a copper(II)‐L‐ornithine ternary complex as selector

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