Biomedical Engineering – From Theory to Applications

Column Coupling Electrophoresis in Biomedical Analysis
1997, 1998). However, the efficiency and peak capacity of high-speed CE separations are
often not high enough to resolve complex mixtures. Recently, improvements in injection
technique and detection limits have improved separation efficiency (Bowser & Kennedy,
2001). In the microdialysis, the minimum volume required for analysis often determines the
rate at which the dialysate can be sampled. On-line microdialysis-derivatization-CE-LIF
assays as proposed by Lada et al. (Lada et al., 1997) (for the instrumental scheme see Fig. 10)
eliminate fraction collection. The separation capillary was coupled to the reactor capillary
via a flow-gated interface which allowed dialysate samples to be automatically injected onto
the separation capillary. This elimination of fraction collection, combined with the high
mass sensitivity of LIF or electrochemical detectors, makes sampling rates on the order of
seconds possible (Thompson et al., 1999; Lada et al., 1997, 1998). The microdialysis-CZE-LIF
system with on-line derivatization has the advantage of simultaneously obtained high
relative recoveries and good temporal resolution with (in-vivo) microdialysis sampling for
the real biological system (brain) (Lada et al., 1997).
Fig. 10. Diagram of the microdialysis:CZE-LIF system with on-line derivatization. Reprinted
from ref. (Lada et al., 1997), with permission.
3.2 Microchip format
Developments in the fields of microfluidics and microfabrication during the last 15 years
have given rise to microchips with broad ranges of functionality and versatility in the areas
of bioanalysis such as clinical applications (Li & Kricka, 2006) and chiral separations (Belder,
2006). Microfluidic devices such as microchips can provide several additional advantages
over electromigration techniques performed in capillary format. The heat dissipation is
much better in chip format compared with that in a capillary and therefore higher electric
fields can be applied across channels of microchip. This fact enables, along with a
considerably reduced length of channels, significant shortening of separation time
(millisecond analysis time is possible to achieve, see e.g. (Belder, 2006)). Sample and reagent
consumption is markedly reduced in microchannels. Hence, microchip capillary
electrophoresis (MCE) can provide a unique possibility of ultraspeed separations of
microscale sample amounts. Applicable are both electrophoretic (Gong & Hauser, 2006;
Belder, 2006) as well as electrochromatographic modes (Weng et al., 2006).
In practice, however, the resolution achievable in MCE devices is often lower compared to
that obtainable in classical CE utilizing considerably longer separation capillaries. In order
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