Enantioseparation by Capillary Electrophoresis Using Ionic Liquids as Chiral Selectors

ABSTRACT

Capillary electrophoresis (CE) is one of the most widely employed analytical techniques to achieve enantiomeric separations. In spite of the fact that there are many chiral selectors commercially available to perform enantioseparations by CE, one of the most relevant topics in this field is the search for new selectors capable of providing high enantiomeric resolutions. Chiral ionic liquids (CILs) have interesting characteristics conferring them a high potential in chiral separations although only some of them are commercially available.

The aim of this article is to review all the works published on the use of CILs as chiral selectors in the development of enantioselective methodologies by CE, covering the period from 2006 (when the first research work on this topic was published) to 2017. The use of CILs as sole chiral selectors, as chiral selectors in dual systems or as chiral ligands will be considered. This review also provides detailed analytical information on the experimental conditions used to carry out enantioseparations in different fields as well as on the separation mechanism involved.

KEYWORDS:

• Capillary electrophoresis
• chiral analysis
• chiral ionic liquids
• chiral selector
• enantioseparation

Abbreviations

L-UCPB	=	undecenoxycarbonyl-L-pryrrolidinol bromide
L-UCLB	=	undecenoxycarbonyl-L-leucinol bromide
[EtChol][NTf2]	=	(R)-N,N,N-trimethyl-2-aminobutanol-bis(trifluoromethane-sulfon)imidate
[DMP][NTf2]	=	(+)-N,N-dimethylephedrinium-bis(trifluoromethanesulfon)imidate
[HPTMA-β-CD][BF4]	=	6-O-2-hydroxypropyltrimethylammonium-β-cyclodextrin tetrafluoroborate
L-AlaC1Lac	=	L-alanine methyl ester lactate
L-AlaC2Lac	=	L-alanine ethyl ester lactate
L-AlaC4Lac	=	L-alanine tert butyl ester lactate
D-AlaC4Lac	=	D-alanine tert butyl ester lactate
L-AlaC4NTf2	=	L-alanine tert butyl ester bis(trifluromethane)sulfonamide
[TMA]+[LA]−	=	tetramethylammonium-lactobionate
(S)-[CHTA][NTf2]	=	S-[3-(chloro-2-hydroxypropyl)trimethylammonium][bis((trifluoro-methyl)sulfonyl)amide
[L-ValC4][NTf2]	=	L-valine tert butyl ester bis(trifluoromethanesulfon)imidate
[D-AlaC4][NTf2]	=	D-alanine tert butyl ester bis(trifluoromethanesulfon)imidate
[EMIm][L-Lactate]	=	1-ethyl-3-methylimidazolium L-lactate
L-UCAB	=	N-undecenoxy-carbonyl-L-alaninol bromide
[BMIm][BLHvB]	=	(1-butyl-3-methylimidazolium(T-4)-bis[(2S)-2-(hydroxy-κO)-3-methyl-butanoato-κO]borate
[BMIm][BSMB]	=	1-butyl-3-methylimidazolium(T-4)-bis[(αS)-α-(hydroxy-κO)-4-methyl-benzeneacetato-κO]borate
[C6mim][L-Pro]	=	1-hexyl-3-methylimidazolium L-proline
[TMA][L-OH-Pro]	=	tetramethylammonium L-hydroxyproline
[L-Phn][CF3COO]	=	L-phenylalaninamide trifluoroacetate
[L-Prn][CF3COO]2	=	L-prolinamide trifluoroacetate
[L-Aln][CF3COO]2	=	L-alaninamide trifluoroacetate
[BMIm][L-Ala]	=	1-butyl-3-methylimidazolium L-alanine
[EMIm][L-Ala]	=	1-ethyl-3-methylimidazolium L-alanine
[HMIm][L-Ala]	=	1-hexyl-3-methylimidazolium L-alanine
[C6mim][L-Lys]	=	1-hexyl-3-methylimidazolium L-lysine
[Epy][L-Lys]	=	1-ethylpyridinium L-lysine
[Bpy][L-Lys]	=	1-butylpyridinium L-lysine
[Hpy][L-Lys]	=	1-hexylpyridinium L-lysine
[Opy][L-Lys]	=	1-octylpyridinium L-lysine
[EMIm][L-Tar]	=	1-ethyl-3-methylimidazolium L-tartrate

Additional information

Funding

The authors would like to thank the Spanish Ministry of Economy and Competitiveness (MINECO) (Project CTQ2016-76368-P) and the University of Alcalá (Project CCG2016/EXP-071) for financial support. M.C.P. also thanks MINECO for her “Ramón y Cajal” research contract RYC-2013-12688, and M.G. thanks the University of Alcalá for her pre-doctoral contract.