4.2 Other Experimental Approaches for Enantioselective
Capillary Electrophoresis
The combination of capillary electrophoresis (CE) and HPLC packings is assumed to
be one of the more exciting developments in separation sciences (Schurig and Mayer
2001; Mangelings et al. 2005a, b; Messina and Sinibaldi 2007). The principles of
this relatively special type of electrochromatography are based on CE separation by
differential movement of neutral compounds through a packed capillary with an
inner diameter of less than 100 μm using electroosmotic flow as the driving force.
The advantage of using electroosmotic flow is increased column efficiency because
of the plug-flow profile and the ability to use smaller particles than those used in
HPLC. Hydraulic flow in HPLC is limited by the column back pressure that results
from the passage of the mobile phase through a packed bed. In CE, electroosmotic
flow is limited only by the voltage applied. The particle diameter of the packing has
no major effect on electroosmotic flow. The minimum particle diameter is more
determined by practical reasons—the smallest particles that can be obtained and the
means to contain them in the fused-silica capillary. Although the technique is still in
the early developmental stage, practitioners using CE have achieved isocratic separations displaying hundreds of thousands of theoretical plates with separation times
comparable to those of HPLC.
An interesting parameter in CE is the nature of the packing material itself. Of
course, the packing has a great influence on the separation (Simo et al. 2010),
because the normal chromatographic interactions occur between the solute, the
mobile phase and the stationary phase. In addition to the chromatographic interactions, the packing material has a profound effect on the electroosmotic flow itself.
These differences in behaviour will presumably lead to studies of optimized packings for CE and most probably to fused-silica deactivation procedures (Alvarez et al.
2018).
4.3 Recent Reviews on Enantiomer-Selective Capillary
Electrophoresis
Recently, several comprehensive reviews and monographs report comprehensively
on the advancements in enantiomer-selective CE-related techniques. We recommend
the following publications for further reading (Simo et al. 2010; Silva 2013;
Giuffrida et al. 2014; Stavrou et al. 2015; El Deeb et al. 2016; Mikuma et al.
2016; Porpiglia et al. 2016; Alvarez et al. 2018; Greno et al. 2018; Hancu et al.
2018; Lancioni et al. 2018; Wahl and Holzgrabe 2018; Zhu and Scriba 2018).
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4 Enantiomer-Selective Electrophoresis and Electrochromatography
Capillary Electrophoresis
The combination of capillary electrophoresis (CE) and HPLC packings is assumed to
be one of the more exciting developments in separation sciences (Schurig and Mayer
2001; Mangelings et al. 2005a, b; Messina and Sinibaldi 2007). The principles of
this relatively special type of electrochromatography are based on CE separation by
differential movement of neutral compounds through a packed capillary with an
inner diameter of less than 100 μm using electroosmotic flow as the driving force.
The advantage of using electroosmotic flow is increased column efficiency because
of the plug-flow profile and the ability to use smaller particles than those used in
HPLC. Hydraulic flow in HPLC is limited by the column back pressure that results
from the passage of the mobile phase through a packed bed. In CE, electroosmotic
flow is limited only by the voltage applied. The particle diameter of the packing has
no major effect on electroosmotic flow. The minimum particle diameter is more
determined by practical reasons—the smallest particles that can be obtained and the
means to contain them in the fused-silica capillary. Although the technique is still in
the early developmental stage, practitioners using CE have achieved isocratic separations displaying hundreds of thousands of theoretical plates with separation times
comparable to those of HPLC.
An interesting parameter in CE is the nature of the packing material itself. Of
course, the packing has a great influence on the separation (Simo et al. 2010),
because the normal chromatographic interactions occur between the solute, the
mobile phase and the stationary phase. In addition to the chromatographic interactions, the packing material has a profound effect on the electroosmotic flow itself.
These differences in behaviour will presumably lead to studies of optimized packings for CE and most probably to fused-silica deactivation procedures (Alvarez et al.
2018).
4.3 Recent Reviews on Enantiomer-Selective Capillary
Electrophoresis
Recently, several comprehensive reviews and monographs report comprehensively
on the advancements in enantiomer-selective CE-related techniques. We recommend
the following publications for further reading (Simo et al. 2010; Silva 2013;
Giuffrida et al. 2014; Stavrou et al. 2015; El Deeb et al. 2016; Mikuma et al.
2016; Porpiglia et al. 2016; Alvarez et al. 2018; Greno et al. 2018; Hancu et al.
2018; Lancioni et al. 2018; Wahl and Holzgrabe 2018; Zhu and Scriba 2018).
68
4 Enantiomer-Selective Electrophoresis and Electrochromatography