Biomedical Engineering – From Theory to Applications

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Biomedical Engineering – From Theory to Applications
Fig. 12. (a) Glass microchip developed for ITP-GE separation, consisting of three separation
elements; (b) protocol of the ITP-GE procedure on the microfluidic device. S: sample; SW:
sample waste; B: background electrolyte; L: leading electrolyte; T: terminating electrolyte. 1)
B and T loading; 2) S and L injection–S at ground, SW at high voltage; 3) stacking–T at
ground, B (well 6) at high voltage; 4) separation–B (well 5) at ground, B (well 6) at high
voltage. The electrodes not in use float. Channel lengths are expressed in mm. Reprinted
from ref. (Huang et al., 2005), with permission.
3.2.1.3 ITP-ITP
Undoubtedly, the use of MCE can be extended advantageously to 2-D ITP separations
(Ölvecká et al., 2001; Kaniansky et al., 2000). CE chip provided with the column-coupling
(CC) configuration of the separation channels and corresponding scheme of the equipment
for the ITP-ITP separations are the same as those ones for ITP-ZE illustrated in Fig.11. ITP-
ITP with the tandem-coupled separation channels makes possible a complete resolution of
various analytes, even the structurally related compounds (such as enantiomers). However,
this can lead only to a moderate extension of the concentration range within which such
analytes can be simultaneously quantified that is pronounced especially for the microfluidic
devices such as MCE. The best results in this respect can be achieved by using a
concentration cascade of the leading ions in the tandem coupled separation channels. Here,
a high production rate, favored in the first separation channel, is followed by the ITP
migration of the analytes in the second channel under the electrolyte conditions enhancing
their detectabilities. This enables to separate structurally related analytes with their higher
concentration ratios, and similarly, trace analyte besides higher concentration of matrix ions
(Ölvecká et al., 2001).
3.2.1.4 ZE-ZE
In a ZE-ZE on-line combination, different separation mechanisms are implemented via
appropriate compositions of the BGE solutions placed into the separation channels prior to
the ZE run. Column switching provides means that significantly enhance resolving power
attainable in the ZE separations performed on the CC chip. These, mainly include (i) on-