Frans_M_Everaerts_Isotachophoresis_378342.pdf

MOVINGBOUNDARY ELECTROPHORESIS
a S
b
0
/ P O \
I
I
I
I
L /a _I I
I I
I
L _ / A
I
J
Fig. 1. Electrophoretic separation of the anionic species A, B and C and -..e cationic species D
along the lines of zone electrophoresis. All compartments are filled with the electrolyte PQ-. The
distances lA, Ig, lc and I,, can be used for the determination of the ionic species A, B, C and D.
(a), Sample injection; (b), all ionic species of the sample are separated.
2.3. PRINClPLE OF MOVING-BOUNDARY ELECTROPHORESIS
S
We shall first consider the separation of anionic species according to the method of
Tiselius. In Fig.2.3a, the anionic species to be separated, mixed with a buffer solution,
fill the lower part of a U-tube while the upper part is filled with the buffer solution. If
an electric current is passed through such a system, the anionic species migrate in the
direction of the anode and, after some time, a partial separation occurs. Two series of
mixed zones are obtained; in front of the original zone are present the zones A and A+ B
and behind the original zone are present B+C and C (see Fig.2.3b), if the effective
mobilities of the ionic species A, B and C decrease in the order mA > mB > mc.
It is also possible to carry out moving-boundary electrophoretic experiments in the
following way. Anionic species can be separated by using a narrow-bore tube as the
separation chamber, connected with anode and cathode compartments. The anode
compartment and narrow-bore tube are filled with an electrolyte, the anionic species of
which is chosen to be more mobile than the anionic species to be separated. The sample
is introduced into the cathode compartment (see Fig.2.4a). The anionic species migrate
towards the anode, and the sample anions can never pass the anionic species of the
leading electrolyte because its effective mobility is higher. The mobilities of the
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