not yet considered as suitable strategies for ultra-trace level environmental pollutant
analysis (Sanchez-Lopez et al. 2016).
Electrophoresis is defined as the motion of substances along a stationary phase in
relation to a liquid when a uniform electric field is applied. Thus, electrophoresis (gel
electrophoresis when a gel is applied as substrate and capillary electrophoresis when
the separation is performed in a capillary) today is mainly applied to the separation of
charged large molecules in biosystems (i.e. DNA, RNA, DNA, RNA) (Smith and
Evans 1994; Baba 1996; Holland et al. 1997; Issaq 2000; Watzig and Gunter 2003;
Suntornsuk 2007). Modified electrophoresis and (micellar) electro-kinetic chromatography (the separation is supported by differential partitioning between micelles
and the surrounding aqueous buffer/mobile phase) are today also used for the
separation of small molecules <800 amu (Alvarez et al. 2018; Zhu and Scriba
2018), including enantiomers of chiral substances (Giuffrida et al. 2014; KapnissiChristodoulou et al. 2014; Stavrou et al. 2015; Ali et al. 2016; Sanchez-Lopez et al.
2016; Chankvetadze 2018; Greno et al. 2018).
For separation in electrophoresis, only charged molecules can be separated. Thus,
target analytes must be kept in a charged state. Due to an improved resolution, today
mainly capillary electrophoresis (CE) is applied. This technique has reduced the
loading capacity, but it has the advantage that EC can easily be combined with
highly sensitive mass-selective detectors (Cherkaoui et al. 2001; Zheng and Shamsi
2003; Visky et al. 2005; Suntornsuk 2007; Gubitz and Schmid 2008; Sanchez-Lopez
et al. 2016). Even if HPLC/UHPLC methods are today more often applied to
enantiomer-selective separation, electrophoresis has distinct advantages when it
comes to the robustness and time requirements of reliable analytical separation
methods. Due to rapid and reliable separation, enantiomer-selective capillary electrophoresis (CE) is often better in a quick screening of large sample numbers.
Furthermore, optimisation and conditioning of optimal separation conditions is
generally faster in CE as compared to HPLC/UHPLC without the need for a
prolonged equilibration time between the chromatographic runs (Sänger-van de
Griend et al. 2013; El Deeb et al. 2016). In addition, and in contrast to many CSPs
in HPLC/ UHPLC, chiral selectors in CE are often used for multi-compound
separation or simultaneous enantiomer-selective separation of several/many chiral
substances (Cui et al. 2018; Lancioni et al. 2018; Liu et al. 2018; Moldovan et al.
2018; Valimana-Traverso et al. 2018). Consequently, the application of CE to
enantiomer-selective separation usually is less costly and more robust compared to
HPLC/UHPLC and can often be applied to multi-compound separations. Thus, for
the human genome project mainly CE methods were used for the characterization of
nucleic acid sequences, associated peptides and proteins (Righetti and Gelfi 1997;
Dovichi and Zhang 2001; Lian and Zhao 2014).
However, a distinct disadvantage of CE is the requirement of charged target
molecules since the separation is mainly governed by the charge difference between
analyte and mobile phase/buffer. Many important target substances are neutral (from
an electrophoretic perspective) and, thus, cannot be separated on CE without
derivatisation or other modification. In order to overcome this restriction, a modified
CE type was developed in the early 1990s, micellar electrokinetic chromatography
66
4 Enantiomer-Selective Electrophoresis and Electrochromatography
analysis (Sanchez-Lopez et al. 2016).
Electrophoresis is defined as the motion of substances along a stationary phase in
relation to a liquid when a uniform electric field is applied. Thus, electrophoresis (gel
electrophoresis when a gel is applied as substrate and capillary electrophoresis when
the separation is performed in a capillary) today is mainly applied to the separation of
charged large molecules in biosystems (i.e. DNA, RNA, DNA, RNA) (Smith and
Evans 1994; Baba 1996; Holland et al. 1997; Issaq 2000; Watzig and Gunter 2003;
Suntornsuk 2007). Modified electrophoresis and (micellar) electro-kinetic chromatography (the separation is supported by differential partitioning between micelles
and the surrounding aqueous buffer/mobile phase) are today also used for the
separation of small molecules <800 amu (Alvarez et al. 2018; Zhu and Scriba
2018), including enantiomers of chiral substances (Giuffrida et al. 2014; KapnissiChristodoulou et al. 2014; Stavrou et al. 2015; Ali et al. 2016; Sanchez-Lopez et al.
2016; Chankvetadze 2018; Greno et al. 2018).
For separation in electrophoresis, only charged molecules can be separated. Thus,
target analytes must be kept in a charged state. Due to an improved resolution, today
mainly capillary electrophoresis (CE) is applied. This technique has reduced the
loading capacity, but it has the advantage that EC can easily be combined with
highly sensitive mass-selective detectors (Cherkaoui et al. 2001; Zheng and Shamsi
2003; Visky et al. 2005; Suntornsuk 2007; Gubitz and Schmid 2008; Sanchez-Lopez
et al. 2016). Even if HPLC/UHPLC methods are today more often applied to
enantiomer-selective separation, electrophoresis has distinct advantages when it
comes to the robustness and time requirements of reliable analytical separation
methods. Due to rapid and reliable separation, enantiomer-selective capillary electrophoresis (CE) is often better in a quick screening of large sample numbers.
Furthermore, optimisation and conditioning of optimal separation conditions is
generally faster in CE as compared to HPLC/UHPLC without the need for a
prolonged equilibration time between the chromatographic runs (Sänger-van de
Griend et al. 2013; El Deeb et al. 2016). In addition, and in contrast to many CSPs
in HPLC/ UHPLC, chiral selectors in CE are often used for multi-compound
separation or simultaneous enantiomer-selective separation of several/many chiral
substances (Cui et al. 2018; Lancioni et al. 2018; Liu et al. 2018; Moldovan et al.
2018; Valimana-Traverso et al. 2018). Consequently, the application of CE to
enantiomer-selective separation usually is less costly and more robust compared to
HPLC/UHPLC and can often be applied to multi-compound separations. Thus, for
the human genome project mainly CE methods were used for the characterization of
nucleic acid sequences, associated peptides and proteins (Righetti and Gelfi 1997;
Dovichi and Zhang 2001; Lian and Zhao 2014).
However, a distinct disadvantage of CE is the requirement of charged target
molecules since the separation is mainly governed by the charge difference between
analyte and mobile phase/buffer. Many important target substances are neutral (from
an electrophoretic perspective) and, thus, cannot be separated on CE without
derivatisation or other modification. In order to overcome this restriction, a modified
CE type was developed in the early 1990s, micellar electrokinetic chromatography
66
4 Enantiomer-Selective Electrophoresis and Electrochromatography