Frans_M_Everaerts_Isotachophoresis_378342.pdf

382 COUNTER FLOW OF ELECTROLYTE
Amaranth red was used as the sample in the operational system at pH 6 (Table 12.1).
Various terminators with different effective mobilities were applied. The results are shown
graphically in Fig.17.5.
These experiments indicated that the disturbance is greater;the smaller are the differ-
ences in effective mobilities. In Fig.17.2 (loo%*), two examples of these boundary
disturbances are shown: (a) the boundary when MES was applied as the terminator and
(b) the boundary when glutamate was applied as the terminator. Experiments with
acetate as the terminator showed that the amaranth red is flushed back into the
terminating reservoir. From these series of experiments, we can conclude that a ‘slow’
terminator is needed in order to prevent too much sample from being flushed back.
Fig.17.5. Disturbance of the zone boundary as a function of the effective mobility of the following
zone. ah = Difference in effective mobility; L = length of the disturbance of the zone boundaries
(mm). This figure can be compared with Fig.17.2 (loo%*). In these experiments hMES = 139;
hglutamate = 77.5; hacetate = 17.5; hamarant,, red = 0; hence Ah refers to the step height of the
amaranth red zone.
Fig.17.6. Isotachopherogram of a standard mixture of anions (Fig.12.5) without (A) and with (B) a
counter flow of electrolyte, showing that several mixed zones disappear. The experiments were carried
out in the operational system at pH 6 (Table 12.1). The differences in heights of the peaks (impurities)
in the linear trace of the W detector should be noted. These zones are marked with asterisks. They
are enriched during the time that the counter flow of electrolyte is applied (see section 10.5). A slight
difference between the recordings from the W absorption detector and the conductivity detector is
always obtained because the diameters of the probe and the PTFE narrow-bore tube are not the same.
Moreover, differences between the traces of the conductivity and the UV absorption detectors can be
expected in (A), because the W absorption detector is mounted closer to the injection point. The
zone of carbonate, marked with a large asterisk, increases with time (see Chapter 9). A = Increasing UV
absorption; R = increasing resistance; t = time.