Frans_M_Everaerts_Isotachophoresis_378342.pdf

392 SIMPLIFIED MODEL OF MOVINGBOUNDARY ELECTROPHORESIS
.t r
2 3 4 5 1 2 3 4 5 1
- -
I
1 2 3 4 5 1 2 3 4
-I
5
Fig.Al. Graphical representation of the theoretical and experimental values for the times of detection
for some cations in a moving-boundary system (see Table Al.). r = ratio I , ItU. s = ionic species:
1 = K'; 2 = Na+; 3 = (CH,),N'; 4 = Li+; 5 = (C,H,),N+. A, B,C, D and E refer to A, B,C, D and E in
Table Al.
now elution phenomena prevail (a uniform voltage gradient is present over the whole of
the capillary tube and consequently the relative times of detection show a Iinear relation-
ship with the mobility).
AS. DISCUSSION
As shown in section A.4, a theoretical relationship between the relative time of detec-
tion and mobility can be used for the determination of effective mobilities, although of
course an experimentally obtained relationship between mobility and relative times of
detection can also be used.
Sometimes, disturbances during isotachophoretic analyses can be understood better
by using a moving-boundary model instead of an isotachophoretic model, and an
example was given in section 9.2.1.2. In Fig.9.2, the relationship between the pH of the
terminator and the ratio tl ItU (vb) is given for theoretical and experimental values. This
is, in fact, the separation of a mixture of two cations, viz., a mixture of H' and K: and
it will be clear that different pH values (different concentrations of H’) will cause
different relative velocities of the K' zones.
Moving boundary electrophoresis can hardly be used as an analytical technique. Of
course, separations can be carried out in this way and Fig.A3 shows an electropherogram