Chiral ion‐exchange capillary electrochromatography of arylglycine amides with dextran sulfate as a pseudostationary phase

Abstract

A low-cost tunable chiral ion-exchange capillary electrochromatographic method has been developed for the separation of arylglycine amide racemic mixtures with dextran sulfate (DS) as an anionic and chiral pseudostationary phase and Tris-tartrate as a buffer system. The concentrations of DS and Tris had opposite influences on retention and resolution and could serve as ideal factors to finely tune the running speed and chiral resolution. Tartrate and pH largely impact the separation but pH should be confined within 3.0-5.5, only suitable for coarse tuning, while tartrate was preserved as the key buffering reagent, normally maintained at 40 mmol/L. With a working system composed of 0.1-1.0% DS, 20-60 mmol/L Tris, and 40 mmol/L tartrate at pH 3.50-4.50, the enantioresolution of arylglycine amides was shown to be dependent on their chemical structure: The chiral resolution increased when the hydrogen at the alpha-amino group or at the p-position of phenyl ring was replaced by other larger group(s) but the resolution decreased when the group at the o- or m-site on the phenyl ring was enlarged. Further, the electronegative substitute of -Cl had larger resolution increment than methyl or methoxy at the position p- of phenyl ring but much lower increment at position m-. It is possible to well explain the resolution variation phenomenon by considering the group resistance and the variation of hydrogen-bonds formed inside the amino amides and between the solutes and DS. The amido group was shown irreplaceable to have chiral resolution with DS alone as an ionic and chiral pseudostationary phase.

Chiral CE of aromatic amino acids by ligand‐exchange with zinc(II)–L‐lysine complex

“…Although ligands are important in performing CLE-CE due to the exchange mechanism [16], the frequently used central ion Cu(II) [17] is also replaceable, namely by Mn(II), Zn(II), Ni(II), and even B(III) or borate [18][19][20][21][22][23][24][25][26]. Kodama et al [23] have demonstrated that borate was effective in the separation of D,L-pantothenic acid because it is capable of forming complex with the cis-1,2-or 1,3-hydroxy.…”

Electrokinetic chromatography with polymeric pseudostationary phases

“…The separation of ten arylglycine amide enantiomers was reported using dextran sulfate as the chiral PSP [40]. Substituent effects indicated that ionic interactions, hydrogen bonding, and steric factors were responsible for the chiral selectivity.…”

Advances in chiral separation using capillary electromigration techniques

“…Chen et al [69] applied dextran sulfate as an anionic pseudostationary phase using Tris/tartrate as a buffer system for the chiral separation of arylglycine amides. The authors call this technique ion-exchange CEC; however, since dextran sulfate forms a pseudostationary phase, it would be rather classified as EKC.…”