Frans_M_Everaerts_Isotachophoresis_378342.pdf

26 PRINCIPLES OF ELECTROPHORETIC TECHNIQUES
species D has migrated in the direction of the cathode. Fig.2.1 lb shows the moving-
boundary procedure. The sample mixture is introduced into the cathode compartment
and the leading electrolyte AE fills the separation chamber and the anode compartment.
The cationic species D thus remains in the cathode compartment and the anionic species
B and C, partially separated, migrate behind the leading electrolyte AE. Note that the
pure zone B and the mixed zone B+C have the counter ionic species of the leading
electrolyte E. The first boundary (with a velocity V,) is sharp (according to the isotacho-
phoretic condition), whereas the separation boundary (with a velocity V*) is not sharp,
as in zone electrophoresis. The zone velocities v* and V1 are different. Fig.2.1 lc shows
the separation procedure for an isotachophoretic system. The sample is introduced
between the leading electrolyte AE and the terminating solution TE. The anionic species
B and C are separated and migrate between the terminator T and the leading ion A. All
zones have equal velocities, and contain the same counter ionic species E. The cationic
species D of the sample has migrated to the cathode. In Fig.2.1 Id, the sample is intro-
duced in an isoelectric focusing system. The point of injection is not important. The ionic
species are eventually separated according to their plvalues and are concentrated on
spots where the pH values are identical with their pl values, their net charges and
velocities then being zero. B and C have migrated towards the anode (lower pH) while
the cationic species D has migrated towards the cathode (higher pH). Only amphiprotic
substances can be separated by this method.