advantages of CZE and CEKC is easy changes of separation media in the method
development, that is, the separation solution can easily be altered to find the
optimum separation media, and one can also use an expensive chiral selector because
of the small amounts of media required. Electrically neutral chiral selectors are
employed for the enantiomer separation of ionic solutes in CZE. Cyclodextrins
have been found to be most effective in CZE for a wide range of ionic drugs. On
the other hand, charged pseudo-stationary phases are added to the running buffer
solution in CEKC. Therefore, CEKC can be applied to both ionic and non-ionic
solutes. Cyclodextrins are also as effective in micellar CEKC as in CZE. In his
review article, Nishi focuses on the enantiomer separation of drugs by different
CEKC modes, mainly micellar CEKC (M-CEKC) and affinity CEKC (A-CEKC)
(Kirschner and Green 2009; Michalska et al. 2017). In the latter mode, biological
components such as proteins or mucopolysaccharides are employed as novel chiral
selectors. CEKC, in which charged cyclodextrins were applied as chiral pseudostationary phases, has been successfully used for enantiomer separations of both
ionic and non-ionic solutes. Diastereomeric analytes have been separated by CEKC
as in reversed-phase HPLC. The same chiral derivatisation reagent as used for HPLC
analysis and typically M-CEKC with SDS have been employed.
During earlier studies, Schurig and co-workers suggested an interesting variation
of CEKC: Dual enantiomer discrimination involving β-cyclodextrin derivatives in
the mobile and the stationary phase. The application of anionic and cationic cyclodextrins, employed as chiral mobile-phase additives, showed an opposite
enantioselectivity compared to CHIRASIL-DEX. Thus, the chiral separation factor
α > 1.5 could be decreased or increased by the addition of these additives (Jakubetz
et al. 1998; Schurig and Wistuba 1999; Wistuba and Schurig 2000).
Examples for successful applications of CE with regard to enantiomer separation
of chiral environmental pollutants can be found in several recent publications and
illustrated impressively the application range of this separation technique (Polcaro
et al. 1999; Bordajandi et al. 2005; Jarman et al. 2005; Asami and Imura 2006; Yi
et al. 2007; Garrison et al. 2008).
Electrophoresis is mainly used for the separation and characterisation of charged
large molecules such as protein and peptides. Thus, with the introduction of large
molecules as pharmaceuticals, food amendments and active ingrediencies in personal care products, electrophoresis has been introduced as analytical key tool in
new research branches such as proteomics, onconomics, toxicogenomics, lipidomics
and genomics (Gomase and Tagore 2008; Gomase et al. 2008; Mann 2008;
Ikonomou et al. 2009; Sheehan and Tyther 2009; Wu and Mohan 2009; Iadarola
et al. 2016; Di Venere et al. 2017).
During the past decade, electrophoresis and related separation techniques also
developed into a versatile and complementary analytical tool for the enantiomerselective separation of chiral organic substances both for industrial applications
including the development of new pharmaceuticals and other medical aids (El Deeb
et al. 2016; Zhu and Scriba 2018). Due to challenges in hyphenation with
ultrasensitive detection systems, electrochromatography and electrophoresis are
4.1 Enantiomer-Selective Capillary Electrophoresis
65
development, that is, the separation solution can easily be altered to find the
optimum separation media, and one can also use an expensive chiral selector because
of the small amounts of media required. Electrically neutral chiral selectors are
employed for the enantiomer separation of ionic solutes in CZE. Cyclodextrins
have been found to be most effective in CZE for a wide range of ionic drugs. On
the other hand, charged pseudo-stationary phases are added to the running buffer
solution in CEKC. Therefore, CEKC can be applied to both ionic and non-ionic
solutes. Cyclodextrins are also as effective in micellar CEKC as in CZE. In his
review article, Nishi focuses on the enantiomer separation of drugs by different
CEKC modes, mainly micellar CEKC (M-CEKC) and affinity CEKC (A-CEKC)
(Kirschner and Green 2009; Michalska et al. 2017). In the latter mode, biological
components such as proteins or mucopolysaccharides are employed as novel chiral
selectors. CEKC, in which charged cyclodextrins were applied as chiral pseudostationary phases, has been successfully used for enantiomer separations of both
ionic and non-ionic solutes. Diastereomeric analytes have been separated by CEKC
as in reversed-phase HPLC. The same chiral derivatisation reagent as used for HPLC
analysis and typically M-CEKC with SDS have been employed.
During earlier studies, Schurig and co-workers suggested an interesting variation
of CEKC: Dual enantiomer discrimination involving β-cyclodextrin derivatives in
the mobile and the stationary phase. The application of anionic and cationic cyclodextrins, employed as chiral mobile-phase additives, showed an opposite
enantioselectivity compared to CHIRASIL-DEX. Thus, the chiral separation factor
α > 1.5 could be decreased or increased by the addition of these additives (Jakubetz
et al. 1998; Schurig and Wistuba 1999; Wistuba and Schurig 2000).
Examples for successful applications of CE with regard to enantiomer separation
of chiral environmental pollutants can be found in several recent publications and
illustrated impressively the application range of this separation technique (Polcaro
et al. 1999; Bordajandi et al. 2005; Jarman et al. 2005; Asami and Imura 2006; Yi
et al. 2007; Garrison et al. 2008).
Electrophoresis is mainly used for the separation and characterisation of charged
large molecules such as protein and peptides. Thus, with the introduction of large
molecules as pharmaceuticals, food amendments and active ingrediencies in personal care products, electrophoresis has been introduced as analytical key tool in
new research branches such as proteomics, onconomics, toxicogenomics, lipidomics
and genomics (Gomase and Tagore 2008; Gomase et al. 2008; Mann 2008;
Ikonomou et al. 2009; Sheehan and Tyther 2009; Wu and Mohan 2009; Iadarola
et al. 2016; Di Venere et al. 2017).
During the past decade, electrophoresis and related separation techniques also
developed into a versatile and complementary analytical tool for the enantiomerselective separation of chiral organic substances both for industrial applications
including the development of new pharmaceuticals and other medical aids (El Deeb
et al. 2016; Zhu and Scriba 2018). Due to challenges in hyphenation with
ultrasensitive detection systems, electrochromatography and electrophoresis are
4.1 Enantiomer-Selective Capillary Electrophoresis
65