Frans_M_Everaerts_Isotachophoresis_378342.pdf

MOVINGBOUNDARY ELECTROPHORESIS
0
iuf ter
n
0
buffer
A
A+B
A+B+C
r
0
butter
a b
0
buffer
-C
- B+C
Fig.2.3. Separation according to the Tiselius moving-boundary principle. In (a), the lower tube is
filled with a mixture of the anions A, B and C. Specific buffers need to be applied for optimal
separation. In (b), it is shown that zones exist on both the front and rear sides, vii., A, A+B and
A+B+C, and A+BtC, BtC and C, respectively.
A+B+C
B and C. Substance B, mixed with A, forms the second sample zone after the pure A
zone. The third zone contains the mixture At B+C.
This method can be compared with frontal analysis in chromatography. In moving-
boundary electrophoresis, the zones generally contain more ionic species of the sample.
The composition of the sample plays an important role in the determination of the
concentrations, pH values and conductivities of the different zones. This situation
contrasts with that in isotachophoresis, where all of these quantities are independent of
the quantitative composition of the sample. A quantitative description of this method
is given in Section 4.2. As will be clear after the description of isotachophoresis, the first
zone in moving-boundary electrophoresis has a self-correcting effect, so that the first
boundary will be sharp. All other zones are not sharp, although this influence is generally
smaller than in zone electrophoresis. In Appendix A, a method is given with which
effective mobilities can be measured by using moving-boundary electrophoresis. Fig.2.4
shows the temperature, voltage gradients and electrical resistances for the different zones.
All of these quantities show similar relationships.
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