Frans_M_Everaerts_Isotachophoresis_378342.pdf

236 INSTRUMENTATION
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Time
Chloride
min.
Fig.7.21. Isotachophoretic separation of formate and acetate without (a) and with (b) a counter flow
of electrolyte. The experiments were carried out in the operational system at pH 6 (Table 12.1) with
glutamic acid as terminating electrolyte. Detection was carried out with a thermocouple mounted at
a distance of about 50 cm from the injection point. The electric current was stabilized by the circuit
shown in Fig.7.20. The thermocouple for regulation was mounted at a distance of about 25 cm
from the injection point. The traces show that the electric current decreases (lower temperature) if
a hot zone passes the regulating thermocouple. As soon as the terminating ion is below the regulation
thermocouple, the electric current is stabilized at imin.. Trace (b) shows that equilibrium is achieved
between the counter flow of electrolyte and the electric current. Traces (a) and (b) show that the
isotachopherograms finally obtained are similar. These isotachopherograms are not given to show the
usefullness of a counter flow of electrolyte, but only to demonstrate current stabilization via LDR
and the possibility of using a counter flow of electrolyte (see Chapter 17).
and the isotachopherogram that can be expected. The recording is performed with a
thermometric detector (copper-constantan thermocouple). In this experiment, therefore,
two thermocouples were mounted around the narrow-bore tube, one at the beginning
of the narrow-bore tube, which was used for the LDR regulation during the counter flow
of electrolyte period, and the other at the end of the narrow-bore tube, which was used
for the detection. Because more advanced systems are considered later, further isotacho-
pherograms with this type of regulation will not be shown. The experimental conditions
for the isotachopherograms shown in Fig.7.21, however, will be given.
The analysis was performed in the operational system at pH 6 (Table 12.1) with
chloride as the leading ion and glutamate as the terminating ion. The aluminium block