Frans_M_Everaerts_Isotachophoresis_378342.pdf

HIGH-FREQUENCY CONDUCTIVITY DETECTION
i- h
100
50-
0-
I, ,
20
1
40
1 -
I
60 80
T OC
Fig.6.7. Temperature differences expected when isotachophoretic experiments are carried out in
narrow-bore tubes hanging free in air. The temperatures were measured in the operational system at
pH 6 (Table 12. l), with chloride (0.01 N) as the leading ion (B) and glutamate as the terminating ion
(A). The values on the arrows indicate the direct driving current (B for the leading electrolyte and A
for the terminating electrolyte). T= Increasing temperature; h(mm) = step height as found in the
linear trace of the thermometric detector. The direct driving currents are given in @A.
The high-frequency conductivity detector needs good shielding [21] and zone lengths
of 2 mm can be detected. The reproducibility, however, is poor. The development of this
type of detector is in the initial phase, so that it would be premature to state that it is
possibly the detector of the future for isotachophoresis.
6.3.2. Construction
The conductivity changes that occur during an analysis inside the narrow-bore tube of
the isotachophoretic equipment can be measured with the circuitry shown schematically
in Fig.6.8.
The signal produced by the generator is led via the symmetry transformer TI (coil ratio
1 : 10) to the emitting electrodes El and E2. Two trimmers, the capacitors C3 and C4,
permit exact symmetry of the high-frequency signal on the emitting electrodes to earth.
131