Frans_M_Everaerts_Isotachophoresis_378342.pdf

EXAMPLES
Choice of solvent.
Can water be used?
NO -
YES - Look for another
solvent **
I
in chosen solvent
Choose several electrolyte
systems that could be
possible*
c
YES t
with computer program an
optimal electrolyte system
can be calculated
I -
NO
-
Follow experimental method
in order to find an
optimal system
Separations can be
carried out?
If no separations can be
carried out because the
differences in effective
mobilities are too small,
look for another solvent
+
t
Electrolyte system
can be chosen
*This step is very important. Here one must take into account all possibilities
dependent on the sample given. Keep in your mind factors such BS complex
formation, precipitations, pH, the choice of leading and terminating ionic
species, concentrations etc.
**Consider the choice of basic and acidic media. Consider also the possibility
that the substances must take a charge.
Fig.5.4. Scheme for the choice of an electrolyte system.
total current. Hence the effective current carried by the anions is very small, so that long
analysis times can be expected (small step heights may be the result). We can choose a
pH, of about 5 or above, at which level both anionic species are nearly completely
ionized. If the pK values are 5 and 7 and the mobilities remain 30 and 50, for instance,
we could apply a combination of separations according to pK values and mobilities. At
a pH of about 6, the effective mobility of anion A would be nearly 50, but that of anion
B would be about 3 because its degree of dissociation is about 0.1. In that event, a
terminating anionic species with an effective mobility of less than 3 should be used.
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