Chapter 4
Enantiomer-Selective Electrophoresis
and Electrochromatography
Enantioselective separations by capillary electrophoresis (CE) have rapidly attracted
attention in the early 1980s as a promising field of pharmaceutical sciences after the
innovative work of Jorgenson (1988) and by the group of Terabe (Nishi et al.
1990a, b). In 1987, CE instruments became commercially available, largely stimulated by pharmaceutical, clinical and biomedical demands. For a brief introduction
into this technique, the reader may wish to consult updated monographs by Gaal
et al. (1980), Reed (2003), Cohen and Schure (2008), Volpi and Maccari (2013),
Granger et al. (2017) or select from a large number recently published review
articles, such as Ramautar (2016), Adam and Vaculovicova (2017), Farcas et al.
(2017), Johnson and Bowser (2017), Zhu and Scriba (2018).
In electrophoresis, a suitable separation can be achieved with one capillary tube
very fast and in high resolution. Performing electrophoresis in small-diameter
capillaries allows the use of very high electric fields, because the small capillaries
efficiently dissipate the heat that is produced. Increasing the electric fields in turn
produces very efficient separations and reduces separation times. Capillaries are
typically of 50 μm inner diameter and 0.5–1.0 m in length. The applied potential is
20–30 kV. Helmholtz already described the phenomenon that an electrical field may
induce an electroosmotic flow within a capillary (Helmholtz et al. 1907). Electroosmotic flow arises from two effects. First, an induced electrical double layer occurs at
the solid–liquid interface of the fused-silica capillary tube and the electrolyte. This
double layer is induced by the presence of ionisable silanol groups at this interface.
In the applied electric field, the positive counter-ions in the mobile phase are mobile
and in slight excess, which causes a net movement of solvated cations toward the
negative electrode. Second, a similar double layer occurs on the silica-based column
packing. The positive counter-ions also cause this double layer to contribute to the
net movement of the cations in an aqueous buffer mobile phase. Due to the
electroosmotic flow, all sample components migrate to the negative electrode. A
small volume of sample (about 10 nL) is injected at the positive end of the capillary
and the separated components are detected near the negative end of the capillary. CE
detection is similar to detectors used in HPLC and includes absorbance,
© Springer Nature Switzerland AG 2021
R. Kallenborn et al., Chiral Environmental Pollutants,
https://doi.org/10.1007/978-3-030-62456-9_4
63
Enantiomer-Selective Electrophoresis
and Electrochromatography
Enantioselective separations by capillary electrophoresis (CE) have rapidly attracted
attention in the early 1980s as a promising field of pharmaceutical sciences after the
innovative work of Jorgenson (1988) and by the group of Terabe (Nishi et al.
1990a, b). In 1987, CE instruments became commercially available, largely stimulated by pharmaceutical, clinical and biomedical demands. For a brief introduction
into this technique, the reader may wish to consult updated monographs by Gaal
et al. (1980), Reed (2003), Cohen and Schure (2008), Volpi and Maccari (2013),
Granger et al. (2017) or select from a large number recently published review
articles, such as Ramautar (2016), Adam and Vaculovicova (2017), Farcas et al.
(2017), Johnson and Bowser (2017), Zhu and Scriba (2018).
In electrophoresis, a suitable separation can be achieved with one capillary tube
very fast and in high resolution. Performing electrophoresis in small-diameter
capillaries allows the use of very high electric fields, because the small capillaries
efficiently dissipate the heat that is produced. Increasing the electric fields in turn
produces very efficient separations and reduces separation times. Capillaries are
typically of 50 μm inner diameter and 0.5–1.0 m in length. The applied potential is
20–30 kV. Helmholtz already described the phenomenon that an electrical field may
induce an electroosmotic flow within a capillary (Helmholtz et al. 1907). Electroosmotic flow arises from two effects. First, an induced electrical double layer occurs at
the solid–liquid interface of the fused-silica capillary tube and the electrolyte. This
double layer is induced by the presence of ionisable silanol groups at this interface.
In the applied electric field, the positive counter-ions in the mobile phase are mobile
and in slight excess, which causes a net movement of solvated cations toward the
negative electrode. Second, a similar double layer occurs on the silica-based column
packing. The positive counter-ions also cause this double layer to contribute to the
net movement of the cations in an aqueous buffer mobile phase. Due to the
electroosmotic flow, all sample components migrate to the negative electrode. A
small volume of sample (about 10 nL) is injected at the positive end of the capillary
and the separated components are detected near the negative end of the capillary. CE
detection is similar to detectors used in HPLC and includes absorbance,
© Springer Nature Switzerland AG 2021
R. Kallenborn et al., Chiral Environmental Pollutants,
https://doi.org/10.1007/978-3-030-62456-9_4
63