Frans_M_Everaerts_Isotachophoresis_378342.pdf

CONDUCTIVITY DETECTION 133
Fig.6.9. Boundary passage of an isotachophoretically moving zone (cNoride/glutamate) recorded with
a high-frequency conductivity detector (solid line) and compared with the a.c. method of conductivity
determination (broken line), discussed in section 6.4. A small amount of impurity (sulphate) was
detected by the a.c. conductivity detector, which was 'missed' by the high-frequency conductivity
detector. The analysis was performed in the operational system at pH 6 (Table 12.1). The direct driving
current was stabilized at 40 pA. The speed of the recorder paper was 6 cmlmin. R = Increasing electric
resistance: t = time.
electrodes in direct contact with the electrolyte. The high-frequency detector, if it is
possible to make an operational type, still has advantages, however, especially if aggressive
solvents are chosen for electrophoretic analysis. A further small advantage is that the
means of detection does not interfere with the electrophoretic separation procedure.
There is the possibility of making a scanning detector, although in practice deviations in
the resistance of the wall will be greater than the variations in electric conductivity.
Although the detector is not yet operational, Fig.6.9 shows the boundary passage of the
zone chloride/glutamate, carried out in the operational system listed in Table 12.1. If
more ions were introduced, the resolution was found to be greater than that with the
thermometric detector, and the reproducibility was found to be smaller.
6.4. CONDUCTIVITY DETECTION
6.4.1. Introduction
In isotachophoretic analyses, the sample ions separate according to their effective