Inspection of the reversal of enantiomer migration order in ligand exchange micellar electrokinetic capillary chromatography

Abstract

Enantiometers of D,L-phenylalanine were separated by capillary electrophoresis based on the principle of ligand exchange. Copper (II) complex of 4-hydroxy-L-proline was used as chiral selector. The separation and the migration order of D- and L-phenylalanine were strongly affected by adding an anion surfactant sodium dodecylsulfate (SDS). Without SDS in the electrolyte, the separation was also carried out but the resolution was very small. With SDS added into the electrolyte, the resolution decreased with increasing concentration of SDS until 5.0 mM. When the concentration of SDS in the electrolyte was over 5.0 mM, inversion of the migration order of DL-phenylalanine was observed and the resolution was also increased with increasing concentration up to 20 mM. It was interesting to find that the inversion of the migration order took place not only in the enantioscparation but also in the positional isomers. A family of a fluorinated amino acid, o-, m- and p-fluoro-D,L-phenylalanine was separated and the inversion of the migration order is discussed.

Recent advances in amino acid analysis by capillary electrophoresis

“…Recently, LEE has been applied to the enantiomeric separation of dansyl amino acids and a-amino acid or dipeptides. The copper(II) complex of 4-hydroxy-L-proline was used as chiral selector for the enantioseparation of DL-phenylalanine [103]. By adding SDS into the BGE, the resolution decreased on increasing the SDS concentration up to 5 mM, but in a concentration range between 5 and 20 mM -even if an inversion in the migration order was observed -the resolution increased again and became better than the resolution obtained in measurements performed without SDS.…”

Recent progress in capillary electrophoretic analysis of amino acid enantiomers

“…When SDS is added to the metal-CS ligands complex system, both chiral selectivity by the LE principle and high resolution ability for closely resembled analytes by MEKC can be obtained; LE-MEKC mode [162][163][164][165][166][167][168]. Chen et al have clearly demonstrated the effect of SDS on the enantioresolution of DNS-Nva, -Asp and -Val [163].…”

Chiral separation with ligand‐exchange micellar electrokinetic chromatography using a D‐penicillamine‐copper(II) ternary complex as chiral selector

“…Interestingly, addition of SDS above its critical micellar concentration (CMC) in the running buffer greatly enhanced the resolution of the chiral separation. Recently, Chen and Lin et al [6][7][8] carefully studied chiral separation behaviors with and/or without SDS, and a method for the determination of CMC of anionic surfactants based on ligand-exchange mechanism was also proposed [9]. They called the method ligand-exchange micellar electrokinetic chromatography (LE-MEKC), which is a hybrid technique of the ligand-exchange mechanism and MEKC.…”