Frans_M_Everaerts_Isotachophoresis_378342.pdf

282 QUANTITATIVE ASPECTS
curvature of the boundary profile for the determination of very small amounts of UV-
absorbing material [3]. The W-absorbing compound must be sandwiched between two
non-UV-absorbing ions, the UV-absorbing ion ‘coating’ the profile with a small layer.
Because the parabolic profile is about 0.1-0.4 mm, even a layer of 0.01 mm of W-
absorbing component can be detected.
Of course, a calibration graph must be constructed for each component and distur-
bances by electroendosmosis of unwanted hydrodynamic transport influence the quan-
titative results enormously. Another problem may occur if one is interested in the quan-
titative determination of the ion which is the most mobile in the system, i.e., the leading
ion.
Reproducible measurements can be carried out if a sample tap is available. Because
the time of appearance of the leading electrolyte-sample boundary is constant (if the
injection of the sample is reproducible), the retardation in the time of the appearance of
the first sample zone, with an effective mobility smaller than that of the leading ion,
can be used to obtain the quantitative information. A reproducibility of better than 98%
can easily be obtained.
REFERENCES
1 J.L. Beckers and F.M. Everaerts, J. Chromatogr., 71 (1972) 329.
2 F.M. Everaerts, J. Chromatogr., 91 (1974) 823.
3 M. Svoboda and J. Vaci’k, J. Chromatogr., 119 (1976) 539.