Frans_M_Everaerts_Isotachophoresis_378342.pdf

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c
t
CHOICE OF ELECTROLYTE SYSTEMS
Fig.5.3. Difference in the separation according to mobilities and the separation according to pK
values. The electropherograms were obtained with a thermometric detector. The electric current was
stabilized at 70 PA. T = Increasing temperature and t = time. Operational system: A, pH = 6
(Table 12.1); B, system E (Tabie 5.8). 1 = Chloride; 2 = trichloroacetate; 3 = p-chioropropionate;
4 = benzoate; 5 = crotonate; 6 = p-aminobenzoate; 7 = trimethylacetate; 8 = glutamate.
mobilities and concentrations of the impurities and the time required for the analyses.
In a similar way, impurities in the leading electrolyte will remain behind if their effective
mobilities are lower than that of the leading ions. Impurities in the terminating electrolyte
with mobilities lower than that of the terminating ion and impurities in the leading
electrolyte with mobilities higher than that of the leading ion do not affect the separation
procedure.
In experiments with thermocouples as the detector, electrolyte solutions were used
that were later found to be too impure when using detectors with a higher resolving
power such as W and conductivity detectors. Especially in these instances and if very
dilute samples are analyzed, the purity of the electrolyte solutions is very important. The
purity of the electrolyte solutions chosen can be checked by running a blank experiment
without a sample. If a counter flow of leading electrolyte is used in order to extend the
time of analysis, small amounts of impurities can be detected. It is not remarkable that
chemical substances that are chromatographically pure often appear to be very impure in
isotachophoretic analyses.
Sometimes, the rule mL >n~,,,,,~, >m, need not be followed. If one is interested