Frans_M_Everaerts_Isotachophoresis_378342.pdf

CONCLUSION 199
average length of a parabolic profile is commonly about 0.4 mm. This is shown later in
Fig. 17.3, in which the profiles are visible because coloured ions are used. Special calibra-
tion graphs must be prepared for each ionic species.
When using equipment in which high-resolution detectors are mounted, for compounds
present in the range from micromoles to nanomoles (average molecular weight loo), full
qualitative and quantitative results can be obtained; at the picomole level or even lower, in
special cases quantitative results can be obtained, as is discussed above.
6.9. CONCLUSION
The choice of the method of detection, especially in analytical isotachophoresis,
must be carefully considered. All of the types of detectors discussed in this chapter are
not always needed, and for many purposes only one type of detector (specific or
universal, with low or high resolution) is sufficient. Especially if one is interested only in
the amount and/or quality of a single component, a detector of very simple performance
can be chosen*. The choice of the method(s) of detection determines to a great extent the
final construction of the equipment, but also makes demands on the purity of the
chemicals used in the various operational systems.
To compare the various method of detection, Figs.6.50 and 6.51 can be considered.
In Fig.6.50, three isotachopherograms of the test mixture of anions (Fig.6.15), in the
-
a b ' c
Fig.6.50. Isotachophoretic separation of the test mixture of anions (Fig.6.15) in the operational system
histidine/histidine hydrochloride at pH 6 (Table 12.1). Detector used: (a) d.c.; (b) non-linear a.c.;
(c) thermometric. Speed of the recorder chart paper: (a) and (b) 2 cmlmin; (c) 5 mm/min. Average
time of analysis: (a) and (b) 15 min; (c) 45 min. The linear traces should be noted. R = Increasing
electric reisstance; T= increasing temperature; f = time.
*Moreover, the use of thin-wall narrow-bore tubes with a small I.D. (e.g., 0.2 mm) improves the
resolution (Appendix B).
T R