Frans_M_Everaerts_Isotachophoresis_378342.pdf

142 DETECTION SYSTEMS
where Yis the voltage on the potential recorder, and Int and Zero are the positions of
the controls ‘Int’ and ‘Zero’, respectively. The pA meter indicates 50 pA if V, = 0 V and
100 pA if Vh = 10 V. The accuracy in measuring Vin is better than 50 mV. If the ambient
temperature changes from 10 to 35 C, the difference in the measured value of Yb,
which of course does not change during this procedure, is less than 20 mV. In Fig.6.15,
an isotachopherogram of a test mixture of anions in the operational system at pH 6
(Table 12.1) is given. In the conclusion of this chapter, more attention is paid to this
method of detection.
It can be seen that Fig.6.15 is comparable with the linearized isotachopherogram
obtained with the a.c. conductimetric circuit, shown in Fig.6.18; in fact, we did not find
any characteristic differences.
10
10
d.C.
6
-
rO
I
7T/J1 10
Fig.6.15. Isotachopherogram of a test mixture of anions in the operational system at pH 6 (Table 12.1),
as derived from the d.c.-a.c. converter in combination with the circuit shown in Fig.6.18. For
comparison, an isotachopherogram obtained with the circuit shown in Fig.6.18 is also given. This
test mixture was applied in almost all isotachopherograms, for pattern recognition, in order to show
the various effects that may occur if insufficient precautions are taken. The leading electrolyte
consists of 0.01 N hydrochloric acid (pro analysi grade) and histidine, adjusted to pH 6; 0.05% (w/w)
of Mowiol (polyvinylalcohol) was added to the electrolyte. Glutamic acid (0.005 N) was used as the
terminating electrolyte, adjusted to pH cn. 6 by addition of Tris. 1 = Chloride; 2 = sulphate; 3 =
chlorate; 4 = chromate; 5 = malonate; 6 = pyrazole-3,5-dicarboxylate; 7 = adipate; 8 = acetate; 9 =
P-chloropropionate; 10 = glutamate. R = Increasing electric resistance; V = increasing potential gradient;
t = time.
i
8
-
a.c.
1